How to Use a Surface Grinder Machine. Automatic surface grinder

How to Use a Surface Grinder Machine:

A surface grinding machine is used to produce a smooth accurate finish on either metallic or nonmetallic materials. It uses a round rotating abrasive grinding wheel that remains stationary (but rotating) while the feed table (with work attached) is run in a reciprocating motion (left and right) under the grinding wheel. The specific amount of material to remove is determined by lightly touching off on the work with the grinding wheel rotating and feeding the grinding head down a certain distance. W A R N I N G. If a grinding wheel is permitted to exceed the maximum safe speed, it may disintegrate and cause injury to the operator and damage to the grinding machine!

On a Manual Surface Grinder, you will then need to run the table left and right with one hand wheel while cross-feeding with the other hand wheel.
On an Automatic Surface Grinder, you will then be able to run the table left and right automatically while cross-feeding automatically. All you need to do is set the down feed and stroke.

Typically surface grinders can grind within.00010002 but not all surface grinders are created equal. The less expensive models may not hold up to tool room accuracies but could be used effectively to sharpen punches, dies or do repair shop work. The more expensive models will use higher quality spindle bearings and other components and will be better able to attain tool room accuracies.

To use the surface grinder, you must select the correct grinding wheel for the work to be ground. There are different wheels that are best suited for grinding:

High Speed Steel RC 50-68 400 Series Stainless Soft Steels RC 30-45 300 Series Stainless Cast Iron: Ductile Gray Nonferrous Alloys

In each of the categories above you will need to determine wheel type by deciding if you need heavy (.004), moderate (.002-.004) or light stock (.001) removal characteristics. Also, you will need to select a Grit size. 46 grit being for general purpose, 60 grit for commercial finish, 80 grit for fine finish and 120 grit for very fine finishes.

After selecting the correct wheel for your job, visually inspect the wheel for any damage or cracks. If no damage is found install the wheel on your surface grinder, tightening the left-hand spindle nut carefully with a spanner wrench. Make sure you replace the guard covering the wheel, put safety glasses on then turn the spindle on. Step away and let the spindle run for 1 minute to make sure the grinding wheel is running smoothly.

Once the grinding wheel has been dressed it is not recommended to turn the spindle off because turning off the spindle will require the wheel to be dressed again for some concentricity will be lost.

You are now ready to dress the wheel using a single point diamond dressing tool that is placed and held down by the magnetic chuck. A small amount of grinding wheel should be dressed off of the diameter in order to make the wheel run concentric. Place the diamond dresser under the rotating wheel and bring down the grinding head carefully so it just touches the dresser. Sweep the diamond dresser across the rotating wheel using the cross feed (y-axis). Feed the grinding head down.002 then sweep the diamond dresser across the rotating wheel. Repeat until the grinding wheel face is clean and running concentric.

After the wheel is dressed and running concentric you will then be ready to gently touch off on the work (using the spark or layout fluid method). Next, set your “zero” on the down feed handle, raise the head slightly to clear work then the cross feed handle to distance the work from the grinding wheel. Next feed the grinding head down a distance not more then.005. The amount of material being removed will determine how far you can feed the cross-feed in per pass.

The benefits of surface grinding are: • You can grind very hard or abrasive materials • High degree of dimensional accuracy • Produces surface textures of very high finish • Tooling is less expensive • Work holding is easier because of magnetic chuck • Can be done automatically

In short, you will most likely need a surface grinder if you need to provide precision ground surfaces, either for a high surface finish or attaining critical dimensions.

GRINDING MACHINES (originally written by the U.S. Army)

Grinding is the process of removing metal by the application of abrasives which are bonded to form a rotating wheel. When the moving abrasive particles contact the workpiece, they act as tiny cutting tools, each particle cutting a tiny chip from the workpiece. It is a common error to believe that grinding abrasive wheels remove material by a rubbing action; actually, the process is as much a cutting action as drilling, milling, and lathe turning. The grinding machine supports and rotates the grinding abrasive wheel and often supports and positions the workpiece in proper relation to the wheel.

The grinding machine is used for roughing and finishing flat, cylindrical, and conical surfaces; finishing internal cylinders or bores; forming and sharpening cutting tools; snagging or removing rough projections from castings and stampings; and cleaning, polishing, and buffing surfaces. Once strictly a finishing machine, modem production grinding machines are used for complete roughing and finishing of certain classes of work. Grinding machines have some special safety precautions that must be observed. These are in addition to those safety precautions described in Chapter 1.

Grinding machines are used daily in a machine shop. To avoid injuries follow the safety precautions listed below.

W A R N I N G. If a grinding wheel is permitted to exceed the maximum safe speed, it may disintegrate and cause injury to the operator and damage to the grinding machine! Wear goggles for all grinding machine operations. Check grinding wheels for cracks (Ring Test Figure 5-11) before mounting. Never operate grinding wheels at speeds in excess of the recommended speed. Never adjust the workpiece or work mounting devices when the machine is operating. Do not exceed recommended depth of cut for the grinding wheel or machine. Remove workpiece from grinding wheel before turning machine off. Use proper wheel guards on all grinding machines. On bench grinders, adjust tool rest 1/16 to 1/8 inch from the wheel. See figure 5-1.

TYPES OF GRINDING MACHINES

From the simplest grinding machine to the most complex, grinding machines can be classified as utility grinding machines, cylindrical grinding machines. and surface grinding machines. The average machinist will be concerned mostly with floor-mounted and bench-mounted utility grinding machines, bufting machines. and reciprocating surface grinding machines.

Figure 5-1

UTILITY GRINDING MACHINES

The utility grinding machine is intended for offhand grinding where the workpiece is supported in the hand and brought to bear against the rotating grinding abrasive wheel. The accuracy of this type of grinding machine depends on the operators dexterity. skill, and knowledge of the machines capabilities and the nature of the work. The utility grinding machine consists of a horizontally mounted motor with a grinding abrasive wheel attached to each end of the motor shaft.

The electric-motor-driven machine is simple and common. It may be bench-mounted or floor-mounted. Generally, the condition and design of the shaft bearings as well as the motor rating determine the wheel size capacity of the machine. Suitable wheel guards and tool rests are provided for safety and ease of operation. Grinding machines come in various sizes and shapes as listed below.

Floor Mounted Utility Grinding Machine:

The typical floor-mounted utility grinding machine stands waist-high and is secured to the floor by bolts. The floormounted utility grinding machine shown in Figure 5-1 mounts two 12-inch-diameter by 2-inch-wide grinding abrasive wheels. The two wheel arrangement permits installing a coarse grain wheel for roughing purposes on one end of the shaft and a fine grain wheel for finishing purposes on the other end this saves the time that would be otherwise consumed in changing wheels.

Each grinding abrasive wheel is covered by a wheel guard to increase the safety of the machine. Transparent eyeshields. spark arresters. and adjustable tool rests are provided for each grinding wheel. A tool tray and a water pan are mounted on the side of the base or pedestal. The water pan is used for quenching carbon steel cutting took as they are being ground. Using the 12-inch wheel, the machine provides a maximum cutting speed of approximately 5.500 SFPM. The 2-HP electric motor driving this machine has a maximum speed of 1.750 RPM.

Bench Type Utility Grinding Machine:

Like the floor mounted utility grinding machine, one coarse grinding wheel and one fine grinding wheel are usually mounted on the machine for convenience of operation. Each wheel is provided with an adjustable table tool rest and an eye shield for protection. On this machine, the motor is equipped with a thermal over-load switch to stop the motor if excessive wheel pressure is applied thus preventing the burning out of the motor. The motor revolve at 3.450 RPM maximum to provide a maximum cutting speed for the 7 inch grinding wheels of about 6,300 surface feet per minute (SFPM).

Figure 5-2

Bench-Type Utility Drill Grinding Machine:

The bench-type drill grinding machine is intended for drill sharpening. The accuracy of this type of grinder is not dependent on the dexterity and skill of the operator because the drill is placed in a holding device. The holding device places the drill in the correct position for the clearance and included angle. For more information on this machine refer to chapter 4.

Bench-Type Utility Grinding and Buffing Machine:

The bench-type utility grinding and buffing machine is more suitable for miscellaneous grinding, cleaning, and buffing It is not recommended for tool grinding since it contains no tool rests, eyeshields, or wheel guards. This machine normally mounts a 4 inch-diameter wire wheel on one end. The wire wheel is used for cleaning and the abrasive wheel is used for general grinding. One of the two wheels can be removed and a buffing wheel mounted in its place for buffing and polishing. The 1/4-HP electric motor revolves at a maximum of 3,450 RPM. The maximum cutting speed of the 4-inch-diameter wheel is approximately 3,600 SFPM.

Figure 5-3

Bench-Type Tool and Cutter Grinder:

The bench-type tool and cutter grinder, see Figure 5-4, was designed primarily to grind end mills. It can also grind a large variety of small wood and steel cutters as well as slitting saw cutters up to 12 inches in diameter using the saw grinding attachment. Capacity grinder is as follows: of the typical bench-type tool and cutter.

Grinding wheel travel. 7 l/2-inch vertical. Grinding wheel travel. 5 1/2-inch horizontal. Table travel. 6 inches. Slitting saws with attachment. 12-inch diameter. Distance between centers. 14 inches. Swing on centers (diameter). 4 l/2-inch diameter. Swing in work head (diameter). 4 l/2-inch diameter.

Figure 5-4

Nonspecialized cylindrical grinding machines in the Army maintenance system include the tool post grinding machine and the versa mil attachment.

Tool Post Grinding Machine:

The tool post grinding machine, see Figure 5-5, is a machine tool attachment designed to mount to the tool post of engine lathes. It is used for internal and external grinding of cylindrical workplaces. Refer to Chapter 7 for a description of this machine.

Milling and Grinding Lathe Attachment:

Also called a Versa-Mil this attachment is a versatile machine tool attachment that mounts to the carriage of a lathe. It performs internal and external cylindrical grinding among its other functions. Refer to Chapter 9 for a description of this machine.

Figure 5-5

SURFACE GRINDING MACHINE:

The surface grinding machine is used for grinding flat surfaces. The workpiece is supported on a rectangular table which moves back and forth and reciprocates beneath the grinding wheel. Reciprocating surface grinding machines generally have horizontal wheel spindles and mount straight or cylinder-type grinding abrasive wheels.

Figure 5-6

RECIPROCATING SURFACE GRINDING MACHINE:

The reciprocating surface grinding machine is a horizontal- automatic application and recirculation of a coolant to the type surface grinding machine. Workpieces are fastened to table and can be moved beneath the grinding abrasive wheel by hand or power feed. A magnetic chuck may be used for fastening the workpiece to the table. This grinding machine has an internal pump and piping network for automatic application and recirculation of a coolant to the workpiece and wheel. The grinding abrasive wheel, mounted to the horizontal spindle is straight and cuts on its circumferential surface only. Grinding wheel speeds are adjustable.

STANDARD TYPES OF GRINDING WHEELS:

Grinding wheels come in many different sizes, shapes, and abrasives (see Figure 5-7).

Figure 5-7

Straight: Straight wheels, numbers 1, 5, and 7, are commonly applied to internal, cylindrical, horizontal spindle, surface, tool, and offhand grinding and snagging. The recesses in type numbers.5 and 7 accommodate mounting flanges. Type number 1 wheels from 0.006-inch to l/8-inch thick are used for cutting off stock and slotting.

Cylinder: Cylinder wheels, type number 2, may be arranged for grinding on either the periphery or side of the wheel.

Tapered: Tapered wheels, type number 4, take tapered safety flanges to keep pieces from flying if the wheel is broken while snagging.

Straight Cup: The straight cup wheel, type number 6, is used primarily for surface grinding, but can also be used for offhand grinding of flat surfaces. Plain or beveled faces are available.

Flaring Cup: The flaring cup wheel, type number 11, is commonly used for tool grinding. With a resinoid bond, it is useful for snagging. Its face may be plain or beveled.

Dish: The chief use of the dish wheel, type number 12, is in tool work. Its thin edge can be inserted into narrow places, and it is convenient for grinding the faces of form-relieved milling cutters and broaches.

Saucer: The saucer wheel, type number 13, is also known as a saw gummer because it is used for sharpening saws.

The abrasive grains are the cutting took of a grinding wheel. They actually cut small pieces or chips off the work as the wheel rotates. The shape of each grain is irregular with several sharp cutting edges. When these edges grow dull, the forces acting on the wheel tend to fracture the abrasive grains and produce new cutting edges.

Most grinding wheels are made of silicon carbide or aluminum oxide, both of which are artificial (manufactured) abrasives. Silicon carbide is extremely hard but brittle. Aluminum oxide is slightly softer but is tougher than silicon carbide. It dulls more quickly, but it does not fracture easily therefore it is better suited for grinding materials of relatively high tensile strength.

Abrasive grains are selected according to the mesh of a sieve through which they are sorted. For example, grain number 40 indicates that the abrasive grain passes through a sieve having approximately 40 meshes to the linear inch. A grinding wheel is designated coarse, medium, or fine according to the size of the individual abrasive grains making up the wheel.

The abrasive particles in a grinding wheel are held in place by the bonding agent. The percentage of bond in the wheel determines, to a great extent, the hardness or grade of the wheel. The greater the percentage and strength of the bond, the harder the grinding wheel will be. Hard wheels retain the cutting grains longer, while soft wheels release the grains quickly. If a grinding wheel is too hard for the job, it will glaze because the bond prevents dulled abrasive particles from being released so new grains can be exposed for cutting. Besides controlling hardness and holding the abrasive, the bond also provides the proper safety factor at running speed. It holds the wheel together while centrifugal force is trying to tear it apart. The most common bonds used in grinding wheels are vitrified, silicate, shellac, resinoid, and rubber.

Vitrified: The majority of grinding wheels have a vitrified bond. Vitrified bonded wheels are unaffected by heat or cold and are made in a greater range of hardness than any other bond. They adapt to practically all types of grinding with one notable exception: if the wheel is not thick enough, it does not withstand side pressure as in the case of thin cutoff wheels.

Silicate: Silicate bond releases the abrasive grains more readily than vitrified bond. Silicate bonded wheels are well suited for grinding where heat must be kept to a minimum, such as grinding edged cutting tools. It is not suited for heavy-duty grinding. Thin cutoff wheels are sometimes made with a shellac bond because it provides fast cool cutting.

Resinoid: Resinoid bond is strong and flexible. It is widely used in snagging wheels (for grinding irregularities from rough castings), which operate at 9,500 SFPM. It is also used in cutoff wheels.

Rubber: In rubber-bonded wheels, pure rubber is mixed with sulfur. It is extremely flexible at operating speeds and permits the manufacture of grinding wheels as thin as 0.006 inch for slitting nibs. Most abrasive cutoff machine wheels have a rubber bond.

GRADES OF GRINDING WHEEL HARDNESS:

The grade of a grinding wheel designates the hardness of the bonded material. Listed below are examples of those grades:

A soft wheel is one on which the cutting particles break away rapidly while a hard wheel is one on which the bond successfully opposes this breaking away of the abrasive grain.

Most wheels are graded according to hardness by a letter system. Most manufacturers of grinding abrasive wheels use a letter code ranging from A (very soft) to Z (very hard). Vitrified and silicate bonds usually range from very soft to very hard, shellac and resinoid bonds usually range from very soft to hard, and rubber bonds are limited to the medium to hard range.

The grade of hardness should be selected as carefully as the grain size. A grinding abrasive wheel that is too soft will wear away too rapidly, the abrasive grain will be discarded from the wheel before its useful life is realized. On the other hand, if the wheel is too hard for the job, the abrasive particles will become dull because the bond will not release the abrasive grain, and the wheels efficiency will be impaired.

Figure 5-8 illustrates sections of three grinding abrasive wheels with different spacing of grains. If the grain and bond materials in each of these are alike in size and hardness, the wheel with the wider spacing will be softer than the wheel with the closer grain spacing. Thus, the actual hardness of the grinding wheel is equally dependent on grade of hardness and spacing of the grains or structure.

GRINDING WHEEL ABRASIVE

Figure 5-8

ABRASIVE WHEEL STRUCTURE

Bond strength of a grinding wheel is not wholly dependent upon the grade of hardness but depends equally on the structure of the wheel, that is, the spacing of the grain or its density. The structure or spacing is measured in number of grains per cubic inch of wheel volume.

Every grinding wheel is marked by the manufacturer with a stencil or a small tag. The manufacturers have worked out a standard system of markings, shown in Figure 5-9.

For an example use a wheel marked A36-L5-V23. The A refers to the abrasive which is aluminum oxide. The 36 represents the grain size. The L shows the grade or degree of hardness, which is medium. The 5 refers to the structure of the wheel and the V refers to the bond type.

Figure 5-9

STANDARD SHAPES OF GRINDING WHEEL FACES:

Figure 5-10 illustrates standard shapes of grinding wheel faces. The nature of the work dictates the shape of the face to be used. For instance, shape A is commonly used for straight cylindrical grinding and shape E for grinding threads.

Figure 5-10

SELECTION OF GRINDING WHEELS:

Conditions under which grinding wheels are used vary considerably, and a wheel that is satisfactory on one machine may be too hard or soft for the same operation on another machine. The following basic factors are considered when selecting grinding wheels, though it should be understood that the rules and conditions listed are flexible and subject to occasional exceptions.

Tensile Strength of Material:

The tensile of material to be ground is the main factor in the selection of the abrasive to be used. Two types of abrasives are suited to different materials as shown below.

Silicon Carbide: Gray and chilled iron Brass and soft bronze Aluminum and copper Marble and other stone Rubber and leather Very hard alloys Cemented carbides Unannealed malleable iron

Aluminum Oxide: Carbon steels Alloy steels High speed steels Annealed malleable iron Wrought iron Hard bronzes

Factors Affecting the Grain Size:

The softer and more ductile the material, the coarser the grain size. The larger the amount of stock to be removed, the coarser the grain size. The finer the finish desired, the finer the grain size.

Factors Affecting the Grade of Hardness:

The harder the material, the softer the wheel. The smaller the arc of contact, the harder the grade should be. The arc of contact is the arc, measured along the periphery of the wheel, that is in contact with the work at any instance. It follows that the larger the grinding wheel, the greater the arc of contact and, therefore, a softer wheel can be used. The higher the work speed with relation to the wheel speed, the milder the grinding action and the harder the grade should be. The better the condition of the grinding machine spindle bearings, the softer the wheel can be.

Factors Affecting the Structure:

The softer, tougher, and more ductile the material, the wider the grain spacing. The finer the finish desired, the closer, or more dense, the grain spacing should be. Surfacing operations require open structure (wide grain spacing). Cylindrical grinding and tool and cutter grinding are best performed with wheels of medium structure (medium grain spacing).

Factors Affecting Bonding Material:

The factors described below affect the selection of bonding material for the wheel desired. Thin cutoff wheels and other wheels subject to bending strains require resinoid, shellac, or rubber bonds. Solid wheels of very large diameters require a silicate bonds. Vitrified wheels are usually best for speeds up to 6,500 SFPM and resinoid, shellac, or rubber wheels are best for speeds above 6500 RPM. Resinoid, shellac, or rubber bonds are generally best where a high finish is required.

Refer to Table 5-1 in Appendix A for specific requirements for typical grinding and materials (grinding wheel selection and application).

INSPECTION OF GRINDING WHEELS:

When a grinding wheel is received in the shop or removed from storage, it should be inspected closely for damage or cracks. Check a small wheel by suspending it on one finger or with a piece of string. Tap it gently with a light nonmetallic instrument, such as the handle of a screwdriver (Figure 5-11).

Figure 5-11

Check a larger wheel by striking it with a wooden mallet. If the wheel does not give a clear ring, discard it. All wheels do not emit the same tone; a low tone does not necessarily mean a cracked wheel. Wheels are often filled with various resins or greases to modify their cutting action, and resin or grease deadens the tone. Vitrified and silicate wheels emit a clear metallic ring. Resin, rubber, and shellac bonded wheels emit a tone that is less clear. Regardless of the bond, the sound of a cracked wheel is easy to identify.

MOUNTING GRINDING WHEELS:

The proper mounting of a grinding wheel is very important. An improperly mounted wheel may become potentially dangerous at high speeds.

The specified wheel size for the particular grinding machine to be used should not be exceeded either in wheel diameter or in wheel width. Figure 5-12 illustrates a correctly mounted grinding wheel

Figure 5-12

Note that the wheel is mounted between two flanges which are relieved on their inner surfaces so that they support the wheel only at their outer edges. This holds the wheel more securely with less pressure and with less danger of breaking. For good support, the range diameter should be about one-third of the wheel diameter. The spindle hole in the wheel should be no more than 0.002 inch larger than the diameter of the spindle, since a loose fit will result in difficulty in centering the wheel. If the spindle hole is oversize, select another wheel of the proper size. If no others are available, fit a suitable bushing over the spindle to adapt the spindle to the hole. Paper blotters of the proper size usually come with the grinding wheel. If the proper blotters are missing, cut them from heavy blotter paper (no more than 0.025-inch thick:) and place them between the grinding wheel and each flange. The blotters must be large enough to cover the whole area of contact between the flanges and the wheel. These blotters serve as cushions to minimize wheel breakage. When installing the grinding wheel on the wheel spindle, tighten the spindle nut firmly, but not so. tight that undue strain will be put on the wheel.

WHEEL DRESSERS:

Grinding wheels wear unevenly under most general grinding operations due to uneven pressure applied to the face of the wheel when it cuts. Also, when the proper wheel has not been used for certain operations, the wheel may become charged with metal particles, or the abrasive grain may become dull before it is broken loose from the wheel bond. [n these cases, it is necessary that the wheel be dressed or trued to restore its efficiency and accuracy.

Dressing is cutting the face of a grinding wheel to restore its original cutting qualities. Truing is restoring the wheels concentricity or reforming its cutting face to a desired shape. Both operations are performed with a tool called an abrasive wheel dresser (Figure 5- 13).

The hand-held mechanical dresser has alternate pointed and solid discs which are loosely mounted on a pin. This dresser is used to dress coarse-grit wheels and wheels used in hand grinding operations.

Abrasive Stick Dresser:

The abrasive stick dresser comes in two shapes: square for hand use, and round for mechanical use. It is often used instead of the more expensive diamond dresser for dressing shaped and form wheels. It is also used for general grinding wheel dressing.

Abrasive Wheel Dresser:

The abrasive wheel dresser is a bonded silicon carbide wheel that is fastened to the machine table at a slight angle to the grinding wheel and driven by contact with the wheel. This dresser produces a smooth, clean-cutting face that leaves no dressing marks on the work.

Figure 5-13

The diamond dresser is the most efficient for truing wheels for precision grinding, where accuracy and high finish are required.

A dresser may have a single diamond or multiple diamonds mounted in the end of a round steel shank. Inspect the diamond point frequently for wear. It is the only usable part of the diamond, and is worn away it cannot dress the wheel properly.

Slant the diamond 3 to 15 in the direction of rotation and 30 to the plane of the wheel as shown in Figure 5-14 to prevent chatter and gouging. Rotate the diamond slightly in its holder between dressing operations to keep it sharp. A dull diamond will force the abrasive grains into the bond pores and load the face of the wheel, reducing the wheels cutting ability.

Figure 5-14

When using a diamond dresser to dress or true a grinding wheel, the wheel should be turning at, or slightly less than, normal operating speed never at the higher speed. For wet grinding, flood the wheel with coolant when you dress or true it. For dry grinding, the wheel should be dressed dry. The whole dressing operation should simulate the grinding operation as much as possible. Whenever possible, hold the dresser by some mechanical device. It is a good idea to round off wheel edges with a handstone after dressing to prevent chipping. This is especially true of a fine finishing wheel. Do not round off the edges if the work requires sharp corners. The grinding wheel usually wears more on the edges, leaving a high spot towards the center. When starting the dressing or truing operation, be certain that the point of the dressing tool touches the highest spot of the wheel first, to prevent the point from digging in.

Feed the dresser tool point progressively, 0.001 inch at a time, into the wheel until the sound indicates that the wheel is perfectly true. The rate at which you move the point across the face of the wheel depends upon the grain and the grade of the wheel and the desired finish. A slow feed gives the wheel a fine finish, but if the feed is too slow, the wheel may glaze. A fast feed makes the wheel free cutting, but if the feed is too fast, the dresser will leave tool marks on the wheel. The correct feed can only be found by trial, but a uniform rate of feed should be maintained during any one pass.

BUFFING AND POLISHING WHEELS:

Buffing and polishing wheels are formed of layers of cloth felt or leather glued or sewed together to form a flexible soft wheel.

Buffing wheels are generally softer than polishing wheels and are often made of bleached muslin (sheeting), flannel, or other soft cloth materials. The material is cut in various diameters and sewed together in sections which are put together to make up the buffing wheel. The buffing wheel is often slotted or perforated to provide ventilation.

Polishing wheels are made of canvas, felt, or leather sewed or glued together to provide various wheel grades from soft to hard. The harder or firmer wheels are generally used for heavier work while the softer and more flexible wheels are used for delicate contour polishing and finishing of parts on which corners and edges must be kept within rather strict specifications.

Buffing and polishing wheels are charged with abrasives for operation. The canvas wheels are generally suitable for use with medium grain abrasives, while felt, leather, and muslin wheels are suitable for fine grain abrasives. Buffing abrasives are usually made in the form of cakes, paste, or sticks which are applied to the wheel in this form. Polishing abrasives are fixed to polishing wheels with a glue.

A wire wheel consists of many strands of wire bound to a hub and radiating outward from the hub in the shape of a wheel. The wire wheel is used in place of a grinding wheel for cleaning operations such as removal of rust or corrosion from metal objects and for rough-polishing castings, hot-rolled steel, and so forth. The wire wheel fastens to the wheel spindle of the grinding machine in the same manner as a grinding wheel.

LAYING OUT AND MOUNTING WORK:

There are no special rules for laying out work for grinding operations. Most layout requirements will be dictated by the specific grinding machine to be used. In many cases, the workpiece will be turned on a lathe or machined in some other manner before grinding. The grinding is in preparation for the final finishing of the workpiece to the desired dimensions.

In planning work to be ground. the amount of metal to be removed should be based on the capabilities of the grinding machine. If the grinding machine is modern and in good condition, leave as much as l/32-inch or even more on large machine steel parts, but generally not more than l/64-inch on small machine parts.

Figure 5-15

Cylindrical Grinding:

If cylindrical grinding is to be performed, such as grinding of workplaces mounted in the grinding may be done with the workpiece set up between centers, held in a chuck and supported by a center rest, or clamped to a faceplate as in lathe setups.

Offhand grinding requires no mounting of the workpiece. Mounting for cylindrical, surface, and tool and cutter grinding is described below.

Mounting Workpiece for Cylindrical Grinding:

Cylindrical grinding may be done with the workpiece setup between centers, held in the chuck and supported by a center rest, or clamped to the faceplate as in lathe setups.

Use the following methods when mounting the workpiece between centers:

Use a dead center in the tailstock spindle. This method is preferred because it eliminates any error caused by wear in the machines spindle bearings. Before grinding check the accuracy and alignment of centers and correct if necessary. To grind the centers, follow the procedures for grinding lathe centers in Chapter 7. After the centers are accurate, align the centers by one of the methods prescribed for aligning lathe centers. Position the workpiece between the centers, and use a lathe dog to revolve the workpiece.

Use the following methods and procedures when mounting the workpiece for concial grinding.

Workpieces for conical grinding can be set up in a chuck or between centers. The table is swiveled to the required taper by means of the graduations on the end of the table (Figure 5-15). Since the table on a universal grinder is limited as to the degree that it can be swiveled, steep conical tapers are normally ground by swiveling the headstock to the angle of the taper desired (Figure 5-15). Remember when a workpiece is to be conically ground, the workpiece axis and the grinding wheel axis must be at the same height. Otherwise, the workpiece will not be ground at the correct angle.

Workpiece Mounted for Internal Grinding:

Internal grinding is done with the universal tool and cutter grinder with an internal grinding attachment (Figure 5-16). Note that the belt and pulleys are exposed; during actual operation, this area should be covered with a guard. Since internal grinding uses small grinding wheels, the spindle and quill must operate at a high speed to get the required SFPM. Most internal grinding attachments come with several sizes of quills. Use the largest one possible for the hole being ground. The smaller quills tend to spring away from the work easily and produce tapers and irregularities.

Figure 5-16

One condition that is more pronounced in internal grinding than in external grinding is that the larger area of contact may cause the wheel to load and glaze quickly which in turn causes vibration and produces poor surface finishes. Therefore, it is important to pay particular attention to the condition of the wheel and to use either a coarser grain wheel to provide more chip clearance or a softer grade wheel that will break down more easily. During grinding, let the grinding wheel run out of the end of the hole for at least one-half the width of the wheel face but not more than two-thirds. If the wheel clears the work each time the table reciprocates, it will grind bell-mouthed hole because of spring in the quill.

Internal conical tapers can also be ground on a universal grinding machine, using a combination of the rules for external conical grinding and those for straight internal grinding. The main thing to remember is to be sure that the axis of the quill is at center height with the axis of the work.

Mounting Workpiece for Surface Grinding:

A workpiece for surface grinding is usually held to the reciprocating worktable by a magnetic chuck. It may also be held in a vise or clamped directly to the table.

The two types of magnetic chucks are permanent magnet and electric. The electric chucks are built in larger sizes and are more powerful. However, the permanent-magnet chucks are less dangerous, since accidental release of work (due to power failure) is not likely to occur.

Mounting Workpiece for Tool and Cutter Grinding:

A workpiece for tool and cutter grinding is usually held between centers or on a fixture clamped to the table. The workpiece is mounted in the same manner as for cylindrical grinding, except the lathe dog if not used. When a fixture is used, the workpiece is placed in the fixture and the fixture is clamped to the table.

GENERAL GRINDING OPERATIONS:

Efficient grinding depends primarily upon the proper setup of the machine being used. If the machine is not securely mounted, vibration will result, causing the grinder to produce an irregular surface. Improper alignment affects grinding accuracy, and it is good practice to check the security and plumb of the machine every few months. It is advisable to place a strip of cushioning material under the mounting flanges, along with any necessary aligning shims, to help absorb vibration.

When a grinding wheel is functioning properly, the abrasive grains cut very small chips from the workpiece and at the same time a portion of the bond of the wheel is worn away. As long as the bond is being worn away as fast as the abrasive grains of the wheel become dull, the wheel will continue to work well. If the bond is worn away too rapidly, the wheel is too soft and will not last as long as it should. If the cutting grains wear down faster than the bond, the face of the wheel becomes glazed and the wheel will not cut freely.

Precision and semiprecision grinding may be divided into the following classes:

Cylindrical Grinding:

Cylindrical grinding denotes the grinding of a cylindrical surface. Usually, Cylindrical grinding refers to external cylindrical grinding and the term internal grinding is used for internal cylindrical grinding. Another form of cylindrical grinding is conical grinding or grinding tapered workpieces.

Surface Grinding:

Surface grinding is the grinding of simple plain surfaces.

Tool and Cutter Grinding:

Tool and cutter grinding is the generally complex operation of forming and resharpening the cutting edges of tool and cutter bits, gages, milling cutters, reamers, and so forth.

surface, grinder, machine, automatic

The grinding wheel for any grinding operation should be carefully chosen and the workpiece set up properly in the grinding machine. Grinding speeds and feeds should be selected for the particular job. Whenever practical, a coolant should be applied to the point of contact of the wheel and the workpiece to keep the wheel and workpiece cool, to wash away the loose abrasive, and to produce a better finish.

GRINDING MACHINE SPEEDS AND FEEDS:

In grinding, the speed of the grinding wheel in SFPM and the feed of the grinding wheel are as important as, and sometimes more important than, proper wheel selection. Occasionally, the grinder spindle should be checked with a tachometer to make sure it is running at its specified RPM. Too slow a speed will result in waste of abrasive, whereas an excessive speed will cause a hard grinding action and glaze the wheel, making the grinding inefficient. The feed of the grinding wheel will determine to a cetain extent the finish produced on the work and will vary for different types and shapes of grinding wheels.

Safety and Factors Governing Speed:

W A R N I N G. If a grinding wheel is permitted to exceed the maximum safe speed, it may disintegrate and cause injury to the operator and damage to the grinding machine!

The grinding wheel should never be run at speeds in excess of manufacturers recommendations, Usually, each grinding wheel has a tag attached to it which states the maximum safe operating speed.

Condition of the Machine:

Modern grinding machines and machines that are in good condition can safely turn a grinding wheel at speeds greater than machines that are older or in poor condition. Most grinding machines are equipped with spindle bearings designed for certain speeds which should not be exceeded. Poor quality will result from vibrations caused by inadequate rigidity or worn bearings that are not in the best condition. High speeds will intensify these defects.

Material Being Ground:

The material being ground will generally determine the grain, grade, structure, and bond of wheel to be selected. For example, if the wheel is too soft for the material being cut, an increase in speed will make the wheel act harder. Conversely, if the wheel is too hard, as lower speed will make the wheel act softer.

Type of Grinding Wheel:

The type of grinding wheel employed for a particular operation is one of the major considerations in the proper selection of cutting speed. In general practice, the wheel will be selected for the material to be cut. The recommended cutting speed can then be determined by the wheel type, bond, and grade of hardness (Table 5-1 in Appendix A).

Calculating Grinding Wheel Size or Speeds:

Both cutting speeds in SFPM and rotational speed in RPM must be known to determine the size wheel to be used on a fixed-speed grinding machine. To determine the grinding wheel size, use the following formula:

D = 12 x SDFPM divided by RPM

Where SFPM = Cutting speed of wheel (In surface feet per minute). RPM = Revolutions per minute of wheel. D = The calculated wheel diameter (in inches).

To obtain the cutting speed in SFPM when the wheel diameter and RPM are given, use the same formula in a modified form:

SFPM = D x RPM divided by 12

To obtain the rotational speed in RPM when the wheel diameter and desired cutting speed are known use the formula in another modified form:

RPM = 12 SFPM divided by D

NOTE: As a grinding wheel wears down and as it is continually trued and dressed, the wheel diameter decreases, resulting in loss of cutting speed. As this occurs, it is necessary to increase the rotational speed of the wheel or replace the wheel to maintain efficiency in grinding.

Work Speed for Cylindrical Grinding:

In cylindrical grinding, it is difficult to recommend any work speeds since these are dependent upon whether the material is rigid enough to hold its shape, whether the diameter of the workpiece is large or small, and so forth. Listed below are areas to consider when performing cylindrical grinding:

The larger the diameter of the workpiece, the greater is its arc of contact with the wheel. The cutting speed suitable for one diameter of workpiece might be unsuitable for another. The highest work speed that the machine and wheel will stand should be used for roughing. Higher work speeds increase the cutting action of the wheel and may indicate that a harder wheel and a smaller depth of cut be used to reduce wheel wear. The following cylindrical work speeds are only typical: Steel shafts, 50 to 55 FPM Hard steel rolls, 80 to 85 FPM Chilled iron rolls, 80 to 200 FPM Cast iron pistons, 150 to 400 FPM Crankshaft bearings, 45 to 50 FPM C rankshaft pins, 35 to 40 FPM

Work Speed for Surface Grinding:

Surface grinding machines usually have fixed work speeds of approximately 50 SFPM or have variable work speed ranges between 0 and 80 SFPM. As with cylindrical grinding, the higher work speeds mean that more material is being cut per surface foot of wheel rotation and therefore more wear is liable to occur on the wheel.

The feed of the grinding wheel is the distance the wheel moves laterally across the workpiece for each revolution of the piece in cylindrical grinding or in each pass of the piece in surface grinding. The following methods are recommended for determine feeds:

The feed should be proportional to the width of wheel face and the finish desired. In general, The narrower the face of the wheel, the slower must be the traverse speed; the wider the wheel face the faster can be the traverse speed. For roughing, the table should traverse about three quarter the wheel width per revolution or pass of the workpiece. For an average finish, the wheel should traverse one-third to one-half the width of the wheel per revolution or pass of the workpiece. In surface grinding with wheels less than 1 inch in width, the table traverse speed should be reduced about onehalf.

Methods for determining depth of cuts are recommended for determining feeds.

In roughing, the cut should be as deep as the grinding wheel will stand, without crowding or springing the work. The depth of cut also depends on the hardness of the material. In cylindrical grinding, in addition to these factors, the cut depends on the diameter of the work. In any case, experience is the best guide. Generally, a cut of 0.001 to 0.003 inch in depth is used, depending on the size and condition of the grinding machine. For finishing, the depth of cut is always slight, generally from 0.0005 inch to as little as 0.00005 inch. An indication of the depth of cut is given by the volume of sparks thrown off. Also, an uneven amount of sparks indicates that the workpiece or wheel is not concentric.

Most surface grinding machines are equipped with coolant systems. The coolant is directed over the point of contact between the grinding wheel and the work. This prevents distortion of the workpiece due to uneven temperatures caused by the cutting action. In addition, coolant keeps the chips washed away from the grinding wheel and point of contact, thus permitting free cutting.

Clear water may be used as a coolant, but various compounds containing alkali are usually added to improve its lubricating quality and prevent rusting of the machine and workpiece. An inexpensive coolant often used for all metals, except aluminum, consists of a solution of approximately 1/4 pound of sodium carbonate (sal soda) dissolved in 1 gallon of water. Another good coolant is made by dissolving soluble cutting oil in water. For grinding aluminum and its alloys, a clear water coolant will produce fairly good results.

Offhand grinding is the process of positioning and feeding the workpiece against a grinding wheel by hand. Offhand grinding is used for reducing weld marks and imperfections on workpieces, and general lathe tool, planer tool, shaper tool, and drill grinding. Deciding depth of cut and feed is based on the operators knowledge of grinding.

Offhand grinding is performed on utility grinding machines which generally have fixed spindle speeds and fixed wheel size requirements, so that the cutting speed of the wheel is constant and cannot be changed for different materials. Therefore, the operator must use care in feeding and not overload the wheel by taking too heavy a cut, which would cause excess wear to the grinding wheel. Similarly, he must be careful not to glaze the wheel by applying excessive pressure against the wheel.

The one variable factor in most offhand grinding is the selection of grinding abrasive wheels, although limited to one diameter. For example, a softer or harder wheel can be substituted for the standard medium grade wheel when conditions and materials warrant such a change. Lathe tool grinding is described in Chapter 7. Drill sharpening and drill grinding attachments and fixtures are described in Chapter 4.

TOOL AND CUTTER GRINDING:

Grinding Milling Cutters:

Milling cutters must be sharpened occasionally to keep them in good operating condition. When grinding milling cutters, care must be exercised to maintain the proper angles and clearances of the cutter. Improper grinding can result in poor cutting edges, lack of concentricity, and loss of form in the case of formed tooth cutters. Milling cutters cannot be sharpened by offhand grinding. A tool and cutter grinding machine must be used.

Bench-Type Tool and Cutter Grinding Machine:

The bench-type tool and cutter grinding machine described here is typical of most tool and cutter grinding machines. It is designed for precision sharpening of milling cutters, spot facers and counterbores, reamers, and saw blades. The grinding machine contains a l/4-HP electric motor mounted to a swivel-type support bracket which can be adjusted vertically and radically on the grinder column. The column is fixed to the grinder base which contains T-slots for attaching grinder fixtures used to support the tools that are to be ground.

The motor shaft or wheel spindle accepts grinding wheels on each end. One end of the spindle contains a wheel guard and tool rest for offhand grinding of lathe tools and so forth. Cup, straight, and 15 bevel taper abrasive grinding wheels are used with this machine. Fixtures used for grinding tools and cutters include a center fixture for mounting reamers, taps, and so forth between centers; an outside diameter fixture for chucking arbor-type milling cutters and shanked peripheral cutting edge tools; and an end mill fixture for supporting end cutting tools to the grinder base.

Grinding Formed Milling Cutters:

Use the following methods and procedures when grinding formed milling cutters.

Formed milling cutters are usually ground with a cup or dish grinding wheel of medium grain (36 to 60 grain). It is important that formed cutters be ground only on the face, never on the land. Grinding the land destroys the shape of the cutter. Also important, the face must be ground so that the exact rake angle is retained or the cutter will cut unevenly. Formed cutters are ground by radial grinding. Correctly ground cutter teeth are shown at A and B, Figure 5-17. At A, the tooth is ground without rake; only cutters originally shaped without rake should be reground without rake. At B, a correctly ground tooth is shown with positive rake. Rake angles are commonly between 10 and 15 from the radius passing through the cutting edge, 12 being the most commonly used angle. The tooth shown at C, has excessive positive rake this tooth will gouge, making an excessively deep cut, and the cutting edge will dull rapidly with hard materials. The tooth shown at D, Figure 5-17 has negative rake; this tooth will drag and make a shallow cut.

On new cutters, the back (Figure 5-17) of each tooth should be ground accurately before grinding the face. This procedure is recommended so that an accurate reference surface is provided for the index finger of the grinding machine attachment. Another method of assuring this alignment is by mounting another cutter containing the same number of teeth on the same arbor with the cutter being ground. With the second cutter properly aligned and locked in place, the index finger can be used against the second cutters teeth.

NOTE: A positive rake angle is a rake angle that increases the keenness of the cutting edge. A negative rake angle is one that decreases or makes the cutting edge more blunt.

Figure 5-17

The grinding wheel should be set up so that the wheel traverse is aligned with the face of one tooth (Figure 5-18). The alignment should be checked by moving the grinding wheel away from the cutter, rotating the cutter, and rechecking the traverse on another tooth. After this alignment is accomplished, the depth of cut, is regulated by rotating the cutter slightly, thus maintaining the same rake angle on the sharpened cutter. The depth of cut should never be obtained by moving the cutter or grinding wheel in a direction parallel to the wheel spindle. Doing this would change the rake angle of the cutter.

surface, grinder, machine, automatic

Grinding Plain Milling Cutters:

Plain milling cutters with saw-tooth type teeth are sharpened by grinding the lands on the periphery of the teeth. The lands may be ground using a straight grinding wheel or a cupshaped grinding wheel.

Figure 5-18

The important consideration when grinding this type of cutter is the primary clearance angle or relief angle of the land (Figure 5-19). If the primary clearance angle is too large, the cutting edge will be too sharp and the cutter will dull quickly. If the primary clearance angle is too small, the cutter will rub rather than cut and excessive heat will be generated.

Figure 5-19

The primary clearance angle (Figure 5-19) should be between 3 and 5 for hard materials and about 10 for soft materials like aluminum. For cutters under 3 inches in diameter, a larger clearance angle should be used: 7 for hard materials and 12 for soft materials.

The clearance angle for end and side teeth should be about 2 and the face of these cutters should be ground 0.001- or 0.002-inch concave toward the center to avoid any drag.

To grind the lands of milling cutter teeth to primary clearance angle, the teeth are positioned against the grinding wheel below the wheels axis (Figure 5-20).

To obtain the primary clearance angle when grinding with a straight wheel, lower the indexing finger or raise the grinding wheel a distance equivalent to 0.0088 times the clearance angle times the diameter of the grinding wheel. For example, to find the distance below center of the indexing finger (Figure 5-20) for a cutter with a 5 clearance angle, being ground by a straight wheel 6 inches in diameter, the calculation is as follows: 0.0088 x 5 x6 = 0.264 inch. The indexing finger would then be set 0.264 inch below the wheel axis. The milling cutter axis should also be 0.264 inch below the wheel axis.

To obtain the primary clearance angle when grinding with a cup wheel, the formula for a straight wheel is used except that instead of wheel diameter being used in the formula, the cutter diameter is used. In this case, the index finger is set to the calculated distance below the axis of the milling cutter (Figure 5-20) instead of below the axis of the wheel.

Table 5-3 in Appendix A is provided to save time in calculating distances below center for primary clearance angles. The same figures can be used for straight wheel or cup wheel grinding, substituting the wheel diameter for the cutter diameter or vice versa.

The land of each tooth (Figure 5-19) should be from 1/32 to 1/16-inch wide, depending upon the type and size of the milling cutter. As a result of repeated grinding of the primary clearance angle, the land may become so wide as to cause the heel of the tooth to drag on the workpiece. To control the land width, a secondary clearance angle (Figure 5-19) is ground. This angle is usually ground to 30, although the exact angle is not critical. Generally, an angle between 20 and 30 is sufficient to define the land of the tooth.

Grinding End Milling Cutters:

The peripheral teeth of end milling cutters are ground in the same manner as the teeth of a plain milling cutter. When grinding the end teeth of coarse-tooth end milling cutters, the cutter is supported vertically in a taper sleeve of the end mill fixture and then tilted to obtain the required clearance angle. The end mill fixture is offset slightly to grind the teeth 0.001 to 0.002 inch lower in the center to prevent dragging. A dishshaped grinding wheel revolving about a vertical spindle is used to grind end milling cutters.

Figure 5-20

After the milling cutter is ground, the cutting edges should be honed with a fine oilstone to remove any burrs caused by grinding. This practice will add to the keenness of the cutting edges and keep the cutting edges sharper for a longer period of time.

Cylindrical grinding is the practice of grinding cylindrical or conical workplaces by revolving the workpiece in contact with the grinding wheel. Cylindrical grinding is divided into three general operations: plain cylindrical, conical grinding (taper grinding), and internal grinding. The workpiece and wheel are set to rotate in opposite directions at the point of contact (Figure 5-21).

Plain Cylindrical Grinding:

The step-by-step procedure for grinding a straight shaft is given below. The shaft has been roughly turned prior to grinding.

Check and grind headstock and tailstock centers if necessary. Check drilled centers of workpiece for accuracy. Place a grinding wheel of the proper grain, grade, structure, and bond on the wheel spindle. Place wheel guards in position to cover the wheel adequately. Set the proper wheel speed on grinding machine (Table 5-2 in Appendix A). Place the diamond dresser and holder on the machine table and true and dress the grinding wheel. Mount the headstock and footstock on the table. Attach the proper size drive dog on the headstock end of the workpiece. Mount the workpiece between headstock and tailstock centers. Use lubricant (oil and white lead mixture) on tailstock center. Make sure centers fit drill center holes correctly with no play. Set the proper rotational work speed on the wheel head. The general range of work speed for cylindrical grinding is 60 to 100 SFPM. Heavy rough grinding is sometimes performed at work speeds as low as 20 or 30 SFPM. Soft metals such as aluminum are sometimes ground at speeds up to 200 SFPM. Position the table trip dogs to allow minimum table traverse. The wheel should overlap each end of the workpiece not more than one-half the wheel width to assure a uniform straight cut over the length of the workpiece. Calculate the table traverse feed using this formula.

TT = (WW x FF x WRPM) 12 Where TT = Table travel in feet per minute WW = Width of wheel FF = Fraction of finish WRPM = Revolutions per minute of workpiece 12 = Constant (inches per foot)

The fraction of finish for annealed steels is 1/2 for rough grinding and 1/6 for finishing; for hardened steels, the rate is 1/4 for rough grinding and 1/8 for finishing.

For example, a l-inch-wide wheel is used to rough grind a hardened steel cylinder with a work RPM of 300.

Table travel = (1 x 1/4 x 300) 12 = (75) 12 = 6.25 FPM

After the calculations have been completed, set the machine for the proper traverse rate, turn on the table traverse power feed, and grind the workpiece. Check the workpiece size often during cutting with micrometer calipers. Check the tailstock center often and readjust if expansion in the workpiece has caused excessive pressure against the drilled center in the workpiece. The finishing cut should be slight, never greater than 0.001 inch, and taken with a fine feed and a fine grain wheel.

If two or more grinding wheels of different grain size are used during the grinding procedure, each wheel should be dressed and trued as soon as it is mounted in the grinding machine.

Figure 5-21

Conical Grinding:

Most conical grinding is performed in the same manner as plain cylindrical grinding. Once the grinding machine is set up, the table is swiveled until the correct taper per inch is obtained. Steep conical tapers are normally ground by swiveling the headstock to the angle of taper. Whichever method is used, the axis of the grinding wheel must be exactly at center height with the axis of the work.

INTERNAL GRINDING:

The internal grinding attachment is bolted to the wheel head on the universal tool and cutter grinder. The RPM is increased by placing a large pulley on the motor and a small pulley on the attachment.

The workpiece should be set to rotate in the direction opposite that of the grinding wheel. The following step-bystep procedure for grinding the bore of a bushing is outlined below as an example.

Set up the workpiece in an independent chuck and check and adjust its alignment. Mount the internal grinding attachment to the wheel head and adjust its position so that the grinding wheel is centered vertically with the mounted workpiece. True and dress the grinding wheel. Set the proper wheel speed on the grinding machine by adjusting the pulleys and belts connecting the wheel spindle to the drive motor shaft. Set the proper rotational work feed. The speed should be 60 to 100 SFPM. Be sure sufficient clearance is allowed when setting the traversing speed so that the grinding wheel will not strike any part of the workpiece or setup when the wheel is fed into and retracted from the workpiece.

If two or more grinding wheels are used to complete internal grinding, true each wheel after mounting it to the spindle of the internal grinding attachment.

SURFACE GRINDING:

Surface grinding or grinding flat surfaces, is characterized by a large contact area of the wheel with the workpiece, as opposed to cylindrical grinding where a relatively small area of contact is present. As a result, the force of each abrasive grain against the workpiece is smaller than that applied to each grain in cylindrical grinding. In surface grinding the grinding wheel should be generally softer in grade and wider in structure than for cylindrical grinding.

SURFACE GRINDING OPERATION:

The following sequence is provided as a step-by-step example of a typical surface grinding operation:

Adjust the surface grinding machine so that grinding head and worktable are absolutely parallel. Place a grinding wheel of the proper grain, grade, structure, and bond on the wheel spindle. Place the guard over the wheel and check security of all adjustable members of the grinding machine for rigidity and lack of backlash. True and dress the grinding wheel. Mount the workpiece to the worktable. Make sure the surface to be ground is parallel to the worktable and the grinding wheel. Adjust wheel speed, work speed, and work feed. Proceed with grinding, adjusting depth of cut as necessary. Check for accuracy between each cut and determine that the workpiece is square and the wheel is not out of alignment. If it is necessary to use more than one grinding wheel to complete the grinding, each wheel should be trued and dressed after it is mounted.

SPECIAL OPERATIONS ON GRINDING MACHINES:

A wire wheel mounted to a utility grinding machine is used for cleaning operations such as removing rust, paint, or dirt from metal objects. If the utility grinding machine on which the wire wheel is to be mounted is equipped with wheel guards and tool rests, these parts should be removed or swung out of the way so that the objects to be cleaned can be brought against the wheel without interference.

To clean objects with a wire wheel, place the object firmly against the wire wheel. Work the object back and forth across the face of the wheel until all traces of rust, paint, or dirt are removed. Avoid excessive pressure against the face of the wire wheel to prevent spreading the steel wires. Keep the point of contact below the center of the wheel to avoid kickback of the workpiece.

POLISHING, BUFFING, AND LAPPING:

Polishing, buffing, and lapping are three closely related methods for finishing metal parts. The three different methods of finishing are listed below.

Polishing is an abrading process in which small amounts of metal are removed to produce a smooth or glossy surface by application of cushion wheels impregnated or coated with abrasives. Polishing may be used for reduction or smoothing of the surface to a common level for high finish where accuracy is not important, or it may be employed for removing relatively large amounts of material from parts of irregular contour. Rough polishing is performed on a dry wheel using abrasives of No. 60 grain (60 grains per linear inch) or coarser. Dry finish polishing is a similar process where No 70. grain to No. 120 grain abrasives are used. Oiling is the term applied to polishing with abrasive finer than No. 120 grain. In this process, the abrasive is usually greased with tallow or a similar substance.

Buffing is a smoothing operation which is accomplished more by plastic flow of the metal than by abrading. The abrasives are generally finer than those used in polishing and instead of being firmly cemented to the wheel are merely held by a grease cake or similar substance. Buffing is used to produce a high luster or color without any particular regard to accuracy of dimension or plane. Cut down buffing produces a Rapid smoothing action with fast-cutting abrasives and relatively hard buffing wheels. It is accomplished with high speeds and heavy pressures to allow a combined plastic flow and abrading action to occur. Color buffing is the imparting of a high luster finish on the workpiece by use of soft abrasives and soft buffing wheels.

Lapping, like polishing, is an abrading process in which small amounts of material are removed. Unlike polishing, however, lapping is intended to produce very smooth, accurate surfaces, and is never used instead of polishing or buffing when clearance is the only consideration. Lapping is accomplished by charging metal forms called laps with flourfine abrasives and then rubbing the workpiece with the lap. The lap may be of any shape and may be designed to fit into most power machine tools. The only requirements of the lap are that it be of softer material than the material being lapped, and that it be sufficiently porous to accept the imbedded abrasive grain. Common materials for laps are soft cast iron, copper, brass, and lead. Some laps are flat and others are cylindrical to fit on steel arbors for internal lapping of bores. A cutting oil is recommended for most lapping operations.

Polishing and Buffing Speeds:

The proper speed for polishing and buffing is governed by the type of wheel, workpiece material, and finish desired. For polishing and buffing in general where the wheels are in perfect balance and correctly mounted, a speed of approximately 1,750 RPM is used for 6-inch to 8-inch wheels; up to 6-inch wheels use 3,500 RPM. If run at a lower rate of speed, the work tends to tear the polishing material from the wheel too readily, and the work is not as good in quality.

The abrasive grains used for polishing must vary in characteristics for the different operations to which they are applied. Abrasive grains for polishing are supplied in bulk form and are not mixed with any vehicle. The abrasives, usually aluminum oxide or silicon carbide, range from coarse to fine (1 to 20 grains per inch).

Buffing abrasives are comparatively fine and are often made up in the form of paste, sticks, or cakes; the abrasive being bonded together by means of grease or a similar vehicle. The abrasive sizes for buffing are 280, 320, 400, 500, and 600. Some manufacturers use letters and numbers to designate grain size such as F, 2F, 3F, 4F, and XF (from fine to very fine). Pumice, rottenstone, and rouge are often used as buffing abrasives.

Only the finest abrasives are used for lapping. These may be either natural or artificial. Abrasives for lapping range from No. 220 to No. 600 or No. 800 which are very fine flours. Lapping compounds are generally mixed with water or oil so that they can be readily applied to the lap.

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Surface Grinding Machine

You do not have to hurry to buy industrial machines. According to FactorNeed technical group reviews, buying a surface grinding machine includes steps that must be carefully considered and followed. It is also important to pay attention to the parameters that are effective in determining the price of the machine; Because the purpose of buying is to provide a machine with high quality and efficiency but at a reasonable price. Therefore, the parameters of the machine may not be required for the production line, and by removing them or replacing them with other parameters and facilities, a flat surface grinding machine can be provided at a reasonable price.

Important influential factors in the pricing of surface grinding machine:

The first step in buying is to determine the level of expectations and production goals. If the level of expectation from the machine and the purpose of production are not determined, the probability of error in selecting a machine that can meet the expectations of the production line will be very high. The next step is to pay attention to commercial points and technical points. Business points include purchasing, concluding contracts and reviewing the necessary items in purchasing a brand new machine, including ordering goods, payment, after-sales service, installation and commissioning, which will be done after the completion of technical inspections and approval of the machine.

Technical tips refers to the two parts of the technical tips of the machine and the technical tips of the part or parts under production. Technical tips of the machine include facilities, capabilities and equipment installed on the machine. Which can largely determine the characteristics of the machine whether it can be adapted to the production line or not.

The technical points of the part also include all the information about the part or parts that should be produced. The preparation of industrial maps of parts and the inclusion of all relevant information in it can help in the accurate presentation of the machines offered by the manufacturers. Here are 9 important factors in pricing flat bed grinders:

  • Manual or automatic flat grinding machine
  • Dimensions of the desk
  • Maximum length and width of grinding
  • Longitudinal movement size (in manual or automatic mode)
  • Dimensions of sanding wheel (grinding wheel)
  • Spindle speed (axis) of flat grinding wheel
  • Your expected level of flat grinding
  • Flat grinding machine brand
  • Country of manufacturer of flat grinding machine

25 points to consider when buying a flat surface grinding machine:

After determining the mentioned cases and summarizing the results, you can also use the experiences of FactorNeed technical group in the field of purchasing flat surface grinding machines:

surface, grinder, machine, automatic
  • Industrial maps should be prepared from the desired part or parts and all relevant details and information such as dimensions, weight, material, accuracy and tolerances, etc. should be mentioned in it.
  • Communicate your requests and expectations clearly with the manufacturer of flat surface grinding machines.
  • Consider the dimensions of the stone wheels and their material, which is determined according to the type of work pieces and the amount of payment.
  • Pay attention to the dimensions of the flat surface grinding machine table and its range of motion.
  • Specify the speed range of the machine table in rabbit mode and mode while working. Also, specify the amount of load and displacement of the machine in each work cycle.
  • Check the height between the table top of the machine and the center of the stone wheel at the maximum distance.
  • Examine the load capacity of the table.
  • You can specify the type of table holder according to your needs and the type of parts produced. Holders can be used as constraints and fixtures, magnetic table or in the form of three systems.
  • Specify the range of motion of the spindle (vertical or horizontal) and its speed in the rabbit position and in the working position.
  • Determine the degree of accuracy. This amount can have a direct impact on the accuracy of manufactured parts.
  • The power of the spindle motor and its brand and the speed of the stone wheel can be selected in consultation with the manufacturer.
  • The power of the hydraulic motor pump (hydraulic and cooling systems) and its brand can also be selected.
  • The number of machine axes in CNC surface grinding machines is determined according to the buyer’s wishes and the level of expectation from the manufactured parts.
  • Make sure that the equipment and safety devices of the machine are complete.
  • The convenience of the operator when working with the machine and their programming to be done easily.
  • Consider the weight of the machine to prepare the gold for the location of the machine.
  • Measure and match the dimensions of the machine with the intended space for installation.
  • Describe environmental working conditions, including humidity, temperature changes, dust levels, and proximity to other production equipment.
  • Write the maximum sound output of pipe bending machines in decibels (DB) (mostly between 50 and 70 decibels).
  • If the grinding process is the last process you are considering, ask the manufacturer to prepare the conditions in such a way that it leads to the best result and performance.
  • The machine can be powered automatically or by the operator. Describe the type and method of feeding the machine to the manufacturer of the surface grinding machine.
  • If the grinding machine uses an automatic control system, specify the brand and model of its numerical control system. For example, you can use LG, Siemens, ABB, Omron, fanuc brands.
  • It is better to send the technical information and brand of high-consumption parts, wires, hydraulic pipes, workers, rails, brand and model of motors, bearings, keyboards, etc. to the manufacturer.
  • Ask the manufacturer for the electrical circuit diagram of the machine, the list of parts, the connection of the cables, the maintenance manual of the machine and its predicted errors.
  • Enter the necessary agreements regarding after-sales services such as transportation, installation, training, replacement and repair warranty, etc. by the manufacturer in writing and have them signed by both parties.

Surface grinding machine

The surface grinding machine is used to polish and adjust the exact dimensions of the flat surfaces of the workpieces. In flat surface grinding, the workpiece is fixed on the workbench (using a magnetic table or using clamps) and the table passes the workpiece from under the stone wheel (in this case It is of circular stone type) with a back and forth movement or a circular movement. Surface grinders are available both manually and automatically; In the manual type, the amount of loading is done by the operator, but in the type of automatic surface grinding, the loading operation and grinding of all surfaces is done by the machine itself.

10 main applications of surface or flat grinding machine:

  • In mold making and tool making workshop (especially surface grinding machine with reciprocating table)
  • Grinding of flat parts in any size (from small part to steel body of lathe)
  • In heavy grinding operations in production lines (especially vertical surface grinding machine with reciprocating table)
  • For grinding clutches and gears
  • For metal blocks such as car engines
  • Railroad tracks
  • Suspension spring washers and seats
  • Various parts of industrial and non-industrial machines
  • Grinding car rims and pistons
  • The body of industrial machines and.

Advantages of flat surface grinding machine:

  • Surface grinding can grind a wide range of materials. This advantage makes surface grinding machines more useful than other chipping machines such as mills and lathes.
  • Flat stone machine wheels are able to grind parts of different sizes.
  • The surface (or flat) grinding machine can grind to an accuracy of 0.0001 inch. Therefore, in addition to polishing flat surfaces, they can grind parts to exact dimensions with high confidence.
  • Flat surface grinding machines are used not only for metals but also for other materials, including plastics.

Disadvantages of flat surface grinding machine:

  • It requires more time than other chipping machines.
  • It has limitations in grinding in such a way that only flat surfaces can be grinded.
  • It needs high care because it has a high sensitivity.

Types of flat surface grinding machines

Grinding machines can be divided into 4 types based on the direction of the machine axis and the type of table movement; Which include:

  • Types of horizontal surface grinding machine with rotating table
  • Types of horizontal surface grinding machine with reciprocating table
  • Types of vertical surface grinding machine with rotating table
  • Types of vertical surface grinding machine with reciprocating table

The best way to increase the chip removal power of surface grinding machine:

To increase the chip removal power, the spindle (the part on which the stone wheel is mounted) can be slightly angled to reduce friction. In this case, one side of the stone will penetrate more into the piece. It should be noted that due to the reduction in the level of impact of the stone with the workpiece and the pointing of the impact, there is a possibility of hazards such as breakage and throwing particles of the stone wheel around.

The Automatic Surface Grinder for You!

The automatic surface grinder is used to obtain a smooth and fine finish on metallic or non-metallic materials. It uses a circular rotary grinding wheel that remains stationary (but rotates) while the feed table (with the job attached) rotates with a reciprocating motion (left and right) under the grinding wheel.

How to Use a Surface Grinder?

The automatic surface grinder is used to obtain a smooth and fine finish on metallic or non-metallic materials. It uses a circular rotary grinding wheel that remains stationary (but rotates) while the feed table (with the job attached) rotates with a reciprocating motion (left and right) under the grinding wheel.

The specific amount of material to be removed is determined by gently touching the work with the rotating grinding wheel and moving the grinding head a specified distance. W A R N I N G. If a grinding wheel can exceed the maximum safe speed, it may fall apart and cause injury to the operator and damage to the grinder!

On a hand-held surface grinder, you then move the table left and right with one handwheel while the cross feed is done with the other handwheel. Automatic plane grinder in 2 or 3 axes and on an automatic plane grinder, you will be able to automatically move the table left and right during automatic cross feeding. All you need to do is set the down feed and pitch.

Typically, surface grinders can grind in the range of.0001 to.0002, but not all surface grinders are created equal. The cheaper models may not withstand the accuracy of a tool shop, but can be effectively used for sharpening punches, dies, or for workshop work. expensive models will use higher quality spindle bearings and other components and be better able to achieve accuracy in the tool shop.

Surface Grinder Showcase: Equiptop TD/ADC Series

Equiptop offers a wide range of high-precision Automatic Surface Grinders for a wide range of applications. Their CNC controlled models, such as the TD/ADC Series are equipped with state-of-the-art control systems that allow for future-proof Smart machining applications.

Automatic Surface Grinding with Advanced Controls

The TD-Plus control system is a new control system developed in response to the industry’s application of Industry 4.0. It achieves the actual ability of intelligent processing through the operating framework of the digital human-machine interface to shorten processing man-hours.

It can be further operated by the Cloud drive at any time. Monitor the I/O operation information of a single machine/multi-machine to achieve the real-time operation capability of online single-machine/multi-machine Cloud monitoring and equipment maintenance.

At the same time, when the machine is connected to the network system, it is possible to quickly and effectively eliminate the machine abnormality through the application and analysis of big data (including processing parameter storage/fault cause collection/use habit analysis. etc.) when the machine is abnormal.

With this control system, it can greatly reduce the transmission of cognitive errors, and it can further shorten the distance between customers and “EQUIPTOP” Technology, and establish the concept of “the world is close to each other”, so that equipment sales to the world do not have to worry about the loss of service quality.

In addition, the operator can also use the network connection function to view the processing conditions of the equipment, the utilization rate and other functions to maintain the output quality at the best level.

It’s all in the Cloud. Intelligence, Informationization and Networking

TD-Plus combines customer demand orientation and Cloud data feedback as the research foundation. Through multi-departmental discussions such as the sales and service department, it cooperates with the current industry 4.0 as a prototype reference to create a crystallization of wisdom between “EQUIPTOP” Technology and customers.

Intelligence, informationization and networking are brought into the machine tool industry. Through Internet transmission and big data storage, users have more information to refer to and make operations more convenient.

Key Functions of Equiptop’s TD Control System

  • Up to 50 language settings which allows clients in all regions to use the equipment directly and clearly to reduce the development time of the operator.
  • Simple and clear processing (data) operation window. The operator can quickly input grinding data and execute commands such as rough grinding/fine grinding/intermittent no-feed empty grinding. etc.
  • Through Delta human-machine interface, wireless relay server, network transmission and remote monitoring application software. Low inventory and shorten the delivery time of customized products to achieve the operation of Smart factories.
  • Multiple machine tools use Delta’s human-machine interface to connect to the central control room via a local network connection. The brain is used to monitor the production status and process of a single machine/multi-machine.
  • Instant APP mobile phone or tablet. Connect to the machine tool via the network to achieve mobile monitoring.
  • Connect the remote client’s machine tool via the Internet. Monitor alarm messages and observe I/O status. Diagnostic and analysis causes. It’s like visiting the scene in person to improve service efficiency.
  • Exclude machine alarms, production records, grinding wheel usage, maintenance services, maintenance inspections, hydraulic lubrication.
  • Equipped with 24″ ALL IN ONE display screen to enhance the display effect and attractiveness.
  • The system user management function can effectively separate the working authority of the on-site operator and the system maintenance personnel. Hierarchical authority management can make internal operations more concise and efficient, and reduce unnecessary costs and waste.

Choosing the Right Grinding Wheel

To use a surface grinder, you need to choose the right grinding wheel for your job. There are different discs that are best suited for grinding:

Series 400 Stainless steel

In each of the above categories, you will have to specify the type of wheel when deciding whether you need a heavy (.004), moderate (.002-.004), or light (.001) removal characteristics. You also need to select the grain size. Grit 46 for general use, grit 60 for commercial finishes, grit 80 for fine finishes and grit 120 for very fine finishes.

After selecting the correct wheel for the job, visually check for damage or cracks. If no damage is found, install the disc on the plane grinder by carefully tightening the left spindle nut with a spanner. Make sure to attach the wheel cover, put on the safety glasses, and then turn on the spindle. Stand back and let the spindle run for 1 minute to make sure the grinding wheel runs smoothly.

After machining the grinding wheel, it is not recommended to turn off the spindle, because turning off the spindle will require reworking the grinding wheel, which will result in loss of some alignment.

Dressing Your Grinding Wheel

You are now ready to dress the grinding wheel with the diamond single point dressing tool which is placed and held by the magnetic chuck. A small amount of the grinding wheel must be cut off the diameter so that the wheel turns concentrically.

Place the diamond dresser under the rotating wheel and carefully lower the grinding head until it just touches the dresser. Use the cross feed (y axis) to pull the diamond dresser along the rotating wheel. Lower the grinding head by 0.002, then slide the diamond dresser along the rotating wheel. Repeat until the grinding wheel is clean and running concentrically.

After the wheel is ready and the concentric operation is started, you will be ready to gently touch the work (using the spark method or styling fluid). Then set “zero” on the down feed handle, slightly raise the head to clear the work, then the cross feed handle to clear the work away from the wheel.

Then move the grinding head a distance of no more than 0.005. The amount of material removed will determine how far crossfeed can be delivered per passage.

Automatic Surface Grinding Advantages

In short, you will most likely need a surface grinder if you need precision sanded surfaces, whether for a high-quality surface finish or for critical dimensions.

Grinding is the process of removing metal by using abrasives that are combined to form a rotating grinding wheel. When the moving abrasive particles come into contact with the workpiece, they act as tiny cutting tools, and each particle cuts a small chip from the workpiece.

A common misconception is that abrasive wheels remove material by friction; in fact, the process is as much machining as drilling, milling and turning of a lathe. The grinder supports and rotates the grinding wheel, and often supports and positions the workpiece in proper relationship to the grinding wheel.

The grinder is used for roughing and finishing flat, cylindrical and conical surfaces; finishing of inner cylinders or holes; forming and sharpening cutting tools; grabbing or removing rough projections from castings and moldings; and cleaning, polishing and polishing of surfaces.

It used to be just a finishing machine, modern production grinders are used for complete roughing and finishing of certain classes of work. Grinding machines have some special safety precautions that must be observed.

Grinding Machine Safety:

Grinders are used daily in the machine shop. To avoid injury, be sure to follow the precautions below.

WARNING. If a grinding wheel can exceed the maximum safe speed, it may fall apart and cause injury to the operator and damage to the grinder!

Wear safety glasses for all grinder operations.

Check grinding wheels for cracks before assembly.

Never use grinding wheels at speeds exceeding the recommended speed.

Never adjust the workpiece or the fastening elements while the machine is running.

Do not exceed the recommended depth of cut for a grinding wheel or machine.

Remove the workpiece from the grinding wheel before turning off the machine.

Use appropriate disc guards on all grinders.

On bench grinders, adjust the tool rest 1/16 to 1/8 inch from the wheel.

Types of Grinding Machines

Grinders from the simplest to the most complex can be divided into tool grinders, cylindrical grinders. and surface grinders. The average machine operator will mainly deal with bench and floor grinders, tool grinders. and Reciprocating Surface Grinders.

Automatic Surface Grinders on IMTS-Exhibition.com

You can find many automatic surface grinder manufacturers on imts-exhibition.com. Just head to our product section or check out our search function to find hundreds of suppliers in our product database. If you want to learn more about surface grinding related questions and applications make sure to check out our other blog entries.

If you are interested in even more detailed manufacturing-related content make sure to check out our MTS Industry Channel. In this show, we introduce new products and trends while visiting manufacturers in their facilities!

If you have any feedback regarding this article or other suggestions, please send us a message!

MTS gathered worldwide Automatic Surface Grinder manufacturers into this online platform. Browse and search for your next supplier with us.

About the Author

EQUIPTOP company product brand recognition EQUIPTOP, meaning TOP EQUIPMENT top-level equipment intended. From the manual molding grinding machine, the three-axis automatic grinding machine, the NC surface grinding machine, the CNC surface grinding machine, to the CNC computer drilling and tapping center machine and the vertical comprehensive processing Center machine, all products have been carefully innovation and design, each piece is the pursuit of a perfect masterpiece, called the industry pioneer in technology.

The Automatic Surface Grinder for You!

The automatic surface grinder is used to obtain a smooth and fine finish on metallic or non-metallic materials. It uses a circular rotary grinding wheel that remains stationary (but rotates) while the feed table (with the job attached) rotates with a reciprocating motion (left and right) under the grinding wheel.

How to Use a Surface Grinder?

The automatic surface grinder is used to obtain a smooth and fine finish on metallic or non-metallic materials. It uses a circular rotary grinding wheel that remains stationary (but rotates) while the feed table (with the job attached) rotates with a reciprocating motion (left and right) under the grinding wheel.

The specific amount of material to be removed is determined by gently touching the work with the rotating grinding wheel and moving the grinding head a specified distance. W A R N I N G. If a grinding wheel can exceed the maximum safe speed, it may fall apart and cause injury to the operator and damage to the grinder!

On a hand-held surface grinder, you then move the table left and right with one handwheel while the cross feed is done with the other handwheel. Automatic plane grinder in 2 or 3 axes and on an automatic plane grinder, you will be able to automatically move the table left and right during automatic cross feeding. All you need to do is set the down feed and pitch.

Typically, surface grinders can grind in the range of.0001 to.0002, but not all surface grinders are created equal. The cheaper models may not withstand the accuracy of a tool shop, but can be effectively used for sharpening punches, dies, or for workshop work. expensive models will use higher quality spindle bearings and other components and be better able to achieve accuracy in the tool shop.

Surface Grinder Showcase: Equiptop TD/ADC Series

Equiptop offers a wide range of high-precision Automatic Surface Grinders for a wide range of applications. Their CNC controlled models, such as the TD/ADC Series are equipped with state-of-the-art control systems that allow for future-proof Smart machining applications.

Automatic Surface Grinding with Advanced Controls

The TD-Plus control system is a new control system developed in response to the industry’s application of Industry 4.0. It achieves the actual ability of intelligent processing through the operating framework of the digital human-machine interface to shorten processing man-hours.

It can be further operated by the Cloud drive at any time. Monitor the I/O operation information of a single machine/multi-machine to achieve the real-time operation capability of online single-machine/multi-machine Cloud monitoring and equipment maintenance.

At the same time, when the machine is connected to the network system, it is possible to quickly and effectively eliminate the machine abnormality through the application and analysis of big data (including processing parameter storage/fault cause collection/use habit analysis. etc.) when the machine is abnormal.

With this control system, it can greatly reduce the transmission of cognitive errors, and it can further shorten the distance between customers and “EQUIPTOP” Technology, and establish the concept of “the world is close to each other”, so that equipment sales to the world do not have to worry about the loss of service quality.

In addition, the operator can also use the network connection function to view the processing conditions of the equipment, the utilization rate and other functions to maintain the output quality at the best level.

It’s all in the Cloud. Intelligence, Informationization and Networking

TD-Plus combines customer demand orientation and Cloud data feedback as the research foundation. Through multi-departmental discussions such as the sales and service department, it cooperates with the current industry 4.0 as a prototype reference to create a crystallization of wisdom between “EQUIPTOP” Technology and customers.

Intelligence, informationization and networking are brought into the machine tool industry. Through Internet transmission and big data storage, users have more information to refer to and make operations more convenient.

Key Functions of Equiptop’s TD Control System

  • Up to 50 language settings which allows clients in all regions to use the equipment directly and clearly to reduce the development time of the operator.
  • Simple and clear processing (data) operation window. The operator can quickly input grinding data and execute commands such as rough grinding/fine grinding/intermittent no-feed empty grinding. etc.
  • Through Delta human-machine interface, wireless relay server, network transmission and remote monitoring application software. Low inventory and shorten the delivery time of customized products to achieve the operation of Smart factories.
  • Multiple machine tools use Delta’s human-machine interface to connect to the central control room via a local network connection. The brain is used to monitor the production status and process of a single machine/multi-machine.
  • Instant APP mobile phone or tablet. Connect to the machine tool via the network to achieve mobile monitoring.
  • Connect the remote client’s machine tool via the Internet. Monitor alarm messages and observe I/O status. Diagnostic and analysis causes. It’s like visiting the scene in person to improve service efficiency.
  • Exclude machine alarms, production records, grinding wheel usage, maintenance services, maintenance inspections, hydraulic lubrication.
  • Equipped with 24″ ALL IN ONE display screen to enhance the display effect and attractiveness.
  • The system user management function can effectively separate the working authority of the on-site operator and the system maintenance personnel. Hierarchical authority management can make internal operations more concise and efficient, and reduce unnecessary costs and waste.

Choosing the Right Grinding Wheel

To use a surface grinder, you need to choose the right grinding wheel for your job. There are different discs that are best suited for grinding:

Series 400 Stainless steel

In each of the above categories, you will have to specify the type of wheel when deciding whether you need a heavy (.004), moderate (.002-.004), or light (.001) removal characteristics. You also need to select the grain size. Grit 46 for general use, grit 60 for commercial finishes, grit 80 for fine finishes and grit 120 for very fine finishes.

After selecting the correct wheel for the job, visually check for damage or cracks. If no damage is found, install the disc on the plane grinder by carefully tightening the left spindle nut with a spanner. Make sure to attach the wheel cover, put on the safety glasses, and then turn on the spindle. Stand back and let the spindle run for 1 minute to make sure the grinding wheel runs smoothly.

After machining the grinding wheel, it is not recommended to turn off the spindle, because turning off the spindle will require reworking the grinding wheel, which will result in loss of some alignment.

Dressing Your Grinding Wheel

You are now ready to dress the grinding wheel with the diamond single point dressing tool which is placed and held by the magnetic chuck. A small amount of the grinding wheel must be cut off the diameter so that the wheel turns concentrically.

Place the diamond dresser under the rotating wheel and carefully lower the grinding head until it just touches the dresser. Use the cross feed (y axis) to pull the diamond dresser along the rotating wheel. Lower the grinding head by 0.002, then slide the diamond dresser along the rotating wheel. Repeat until the grinding wheel is clean and running concentrically.

After the wheel is ready and the concentric operation is started, you will be ready to gently touch the work (using the spark method or styling fluid). Then set “zero” on the down feed handle, slightly raise the head to clear the work, then the cross feed handle to clear the work away from the wheel.

Then move the grinding head a distance of no more than 0.005. The amount of material removed will determine how far crossfeed can be delivered per passage.

Automatic Surface Grinding Advantages

In short, you will most likely need a surface grinder if you need precision sanded surfaces, whether for a high-quality surface finish or for critical dimensions.

Grinding is the process of removing metal by using abrasives that are combined to form a rotating grinding wheel. When the moving abrasive particles come into contact with the workpiece, they act as tiny cutting tools, and each particle cuts a small chip from the workpiece.

A common misconception is that abrasive wheels remove material by friction; in fact, the process is as much machining as drilling, milling and turning of a lathe. The grinder supports and rotates the grinding wheel, and often supports and positions the workpiece in proper relationship to the grinding wheel.

The grinder is used for roughing and finishing flat, cylindrical and conical surfaces; finishing of inner cylinders or holes; forming and sharpening cutting tools; grabbing or removing rough projections from castings and moldings; and cleaning, polishing and polishing of surfaces.

It used to be just a finishing machine, modern production grinders are used for complete roughing and finishing of certain classes of work. Grinding machines have some special safety precautions that must be observed.

Grinding Machine Safety:

Grinders are used daily in the machine shop. To avoid injury, be sure to follow the precautions below.

WARNING. If a grinding wheel can exceed the maximum safe speed, it may fall apart and cause injury to the operator and damage to the grinder!

Wear safety glasses for all grinder operations.

Check grinding wheels for cracks before assembly.

Never use grinding wheels at speeds exceeding the recommended speed.

Never adjust the workpiece or the fastening elements while the machine is running.

Do not exceed the recommended depth of cut for a grinding wheel or machine.

Remove the workpiece from the grinding wheel before turning off the machine.

Use appropriate disc guards on all grinders.

On bench grinders, adjust the tool rest 1/16 to 1/8 inch from the wheel.

Types of Grinding Machines

Grinders from the simplest to the most complex can be divided into tool grinders, cylindrical grinders. and surface grinders. The average machine operator will mainly deal with bench and floor grinders, tool grinders. and Reciprocating Surface Grinders.

Automatic Surface Grinders on IMTS-Exhibition.com

You can find many automatic surface grinder manufacturers on imts-exhibition.com. Just head to our product section or check out our search function to find hundreds of suppliers in our product database. If you want to learn more about surface grinding related questions and applications make sure to check out our other blog entries.

If you are interested in even more detailed manufacturing-related content make sure to check out our MTS Industry Channel. In this show, we introduce new products and trends while visiting manufacturers in their facilities!

If you have any feedback regarding this article or other suggestions, please send us a message!

MTS gathered worldwide Automatic Surface Grinder manufacturers into this online platform. Browse and search for your next supplier with us.

About the Author

EQUIPTOP company product brand recognition EQUIPTOP, meaning TOP EQUIPMENT top-level equipment intended. From the manual molding grinding machine, the three-axis automatic grinding machine, the NC surface grinding machine, the CNC surface grinding machine, to the CNC computer drilling and tapping center machine and the vertical comprehensive processing Center machine, all products have been carefully innovation and design, each piece is the pursuit of a perfect masterpiece, called the industry pioneer in technology.

We Tested 14 Coffee Grinders—Here Are the Best Ones

Our top picks include the Baratza Virtuoso Coffee Grinder and OXO Brew Conical Burr Coffee Grinder.

Daniel joined the Serious Eats culinary team in 2014 and writes recipes, equipment reviews, articles on cooking techniques. Prior to that he was a food editor at Food Wine magazine, and the staff writer for Time Out New York’s restaurant and bars section.

Straight to the Point

Our favorite coffee grinder for serious coffee geeks who want a lot of control over grind size is the Baratza Virtuoso Coffee Grinder (we also liked the Breville Smart Grinder Pro and the Baratza Encore Conical Burr Coffee Grinder, as a less expensive option). For those looking for a more straightforward burr grinder with fewer grind settings, the OXO Brew Conical Burr Coffee Grinder will serve most people well. And for about 50, the Krups Precision Grinder is our super-budget pick. We also recently reviewed the Fellow Ode Gen 2 and, while pricey, we really liked it.

I can’t tell you how many times I’ve heard a coffee pro say that the single biggest upgrade a person can make at home is to buy a good-quality burr grinder. Less often have I seen other suggestions, like buying a better coffeemaker, learning the ins and outs of brewing, and developing a better sense of one’s own coffee-bean preferences. The grinder recommendation is so common that it invaded my brain, eventually anchoring itself deep in the part responsible for consumerist behavior.

Unable to afford the types of expensive grinders that are always recommended, I did what any scheming compulsive shopper would do: I spent years saving up the unsolicited 25 Starbucks gift cards I received as Christmas stocking stuffers each December. It took about six years before the grinder was within reach, including two very sad years when I believed I had lost four of the cards followed by a bright and shiny day when I found those cards. It culminated in five euphoric minutes visiting Starbucks’ online coffee gear store to order the Baratza Virtuoso I’d been saving to get.

I’ve been very happy with that grinder. It’s allowed me to tinker with my coffee brews, which is something I enjoy doing, and I’m certain I make better coffee as a result. But the question has always lingered: Would every home-brewed coffee drinker really benefit from an expensive grinder? Is that advice truly as universal as so many baristas have made it seem?

So I set out with two objectives for this review. The first is the obvious one: Find the best coffee grinder for the kinds of brewing methods most people do at home, like pour-over, automatic-drip, French press, and AeroPress. But I also wanted to explore whether the “best” grinder is a more relative term than pros often acknowledge. Pros know their subject better than anyone, but—and I say this as someone who can be guilty of it on the cooking side—are often too deep in the details to remember that not everyone notices them or even cares to.

I’ll tell you now my research indicates that not every coffee drinker should splurge on the “best” grinder, and a big part of getting the right grinder is going to depend on knowing what kind of coffee drinker you are. This also means that I’m recommending an unusually large number of products, several of which overlap quite a bit in terms of what they do and how well they do it but differ in price and quality to some degree.

Here are my grinder recommendations, which I arrived at with the input of coffee-making professionals and coffee-drinking civilians. The team at Joe Coffee Company was invaluable in helping me run grinder taste tests and analyses, and conversations with Steve Rhinehart of Prima Coffee Equipment and Nick Cho of Wrecking Ball Coffee Roasters helped deepen my understanding of this piece of coffee gear and the technical details that underpin its use.

Here, too, is a guide to when and where a grinder really matters. Take note, though, that one thing this review is not is a thorough exploration of grinders for espresso—I’ll explain why below.

Editor’s Note

We recently tested the Fellow Ode Gen 2 grinder, an updated version of the grinder we previously tested, and added it as another winner. We also tested coffee grinders from OXO, Capresso, and Zwilling (which weren’t available at the time of our original testing). We’ve added our thoughts on each of these newer models to the bottom of this page. It’s also worth noting that when we initially published this review, our overall top coffee grinder was the Baratza Virtuoso, which has since been replaced by the Virtuoso. It’s comparable, performance-wise, to the Virtuoso, but has a digital display and a 40-second timer.

The Best Coffee Grinder for Serious Coffee Geeks

Baratza Virtuoso Conical Burr Coffee Grinder

Baratza’s Virtuoso coffee grinder is routinely picked by pros as the home grinder to beat, and for good reason. Its well-made conical burrs produce a wide range of grind sizes, the results are consistent, the machine is solidly built from both metal and plastic, and it’s all backed up by good customer service. I don’t love taking apart and reassembling the burr set for cleaning, as it isn’t intuitive enough, but beyond that, this is the grinder to get for serious home-brewed coffee drinkers looking to maximize control over grind size.

Best For: Folks who are well-acquainted with concepts like flow rate, brew time, and extraction level; who use scales to measure everything and know their bean-to-water ratio by weight; who prefer light to medium roasts that present more of a bean’s inherent flavors; and who usually drink their coffee black.

Alternate Best Coffee Grinder Pick

Breville The Smart Grinder Pro

Breville’s Smart Grinder Pro also performed very well in our tests, and it’s worth considering since it costs less than our other top pick, the Baratza Virtuoso. Its grind trends finer than the Virtuoso. Even at its coarsest setting, the results were closer to the medium grind that other machines produced. That potentially makes it less well-suited to making French press and cold brew, but it’ll perform well for most other brewing methods and can even function as an entry-level espresso grinder—something few other home coffee grinders can do.

Best For: The same people who would buy the Virtuoso, but those who are less likely to make press pots or cold brew, and those who may want to casually play with pulling espresso shots.

The Best Budget Coffee Grinder for Coffee Geeks

Baratza Encore Conical Burr Coffee Grinder

There’s a lot to be said for Baratza’s entry-level Encore grinder, which comes in a lighter-weight, all-plastic housing. It packs the same motor as the more expensive Virtuoso, and it includes a slightly less effective burr set that grinds nearly as well as—and slightly more slowly than—the Virtuoso. Also worth knowing is you can upgrade the burr set in the Encore to the one made for the Virtuoso if you do ever end up feeling like the Encore isn’t quite cutting it.

Best For: Anyone considering the Virtuoso but who’s not quite ready to pay the higher price tag.

The Best Coffee Grinder for Most People

OXO Brew Conical Burr Coffee Grinder

Like many of OXO’s products, its burr grinder’s design is simple and intuitive. Even more importantly, it delivers excellent grind consistency given its price tag. This is about as inexpensive as a burr grinder gets before the grind quality really starts to fall off, making it a good starter grinder for most home-brewed coffee drinkers.

Best For: Any coffee drinker who wants more control and a chance to experiment with grind sizes; who wants to begin to explore some of the more detailed coffee-brewing concepts without a huge cost of entry; who likes a good cup but maybe isn’t 100% clear on what terms like TDS (total dissolved solids), acidity, and sweetness mean (at least when discussing a cup of joe).

The Best Super-Budget Burr Grinder

Krups Precision Coffee Grinder

If the price points of our favorite grinders make them an out-of-the-question proposition, and if you’d like to stop using a blade grinder to chop up your beans (after all, it does kinda suck when your coffee tastes like the cumin you also blitzed in there), you can’t beat the price on this Krups model. Its grind is inconsistent, and its build quality leaves a lot to be desired, but you get what you pay for. On the upside, even with the inconsistent grind, you’ll still have more control over your grind size than you would using a blade grinder, and for many people, that’s all that matters.

Best For: Coffee drinkers who tend to buy dark roasts and/or drink their coffee with dairy or sugar; those who want to grind whole beans for fresher flavor and are sick of having to do it in the spice grinder.

The Best Design-Forward Coffee Grinder

Fellow Ode Gen 2 Coffee Grinder

After a lukewarm reception for their first coffee grinder, Fellow re-tooled the anti-static system and overhauled the burr design for the Gen 2 Ode. This version featured some of the most consistent grinding in our testing, great user interface details (like a grind chart under the lid), and virtually no static cling—all in a stylish, small format.

Best For: People who want counter appeal and ease of use and are willing to pay for it. The Ode Gen 2 delivers high-quality grinding and a great user experience while its modern design and small stature look great on most counters.

The Criteria: What We Look for in a Great Coffee Grinder

To understand the importance of a good coffee grinder, you need to have a basic understanding of what happens when coffee is made. Generally speaking, when we brew coffee, our goal is to extract a sufficient amount of desirable soluble molecules from the beans while leaving the undesirable ones behind.

surface, grinder, machine, automatic

If we don’t extract enough of what we want from a bean, the resulting coffee will taste “underextracted.” Underextracted coffee is not necessarily weak coffee. Rather, it’s coffee in which an insufficient amount of the desirable soluble molecules have been pulled out of the beans and dissolved into the water. If you brew a high ratio of coffee beans in water but underextract them, you could end up with coffee that is both strong and underextracted, a seemingly contradictory concept. Underextracted coffees tend to taste more sour—and not in a good way.

Overextracted coffees, on the other hand, have pulled too much from the beans, including unpleasant things we don’t want in the cup. Those coffees often taste harsh and bitter. And just like the seemingly antithetical possibility of a strong underextracted coffee, you can have a weak overextracted coffee, say, by brewing a small amount of coffee relative to the water for too long.

It should go without saying that you can also have weak underextracted coffees, strong overextracted ones, and everything in between.

A grinder plays a pivotal role in coffee extraction because it determines the grind size of the coffee. Grind size can affect extraction in two ways. The first is perhaps the most obvious one: Finely ground coffee has far more surface area than coarsely ground coffee, and that increased surface area makes what’s in the beans more immediately accessible to the hot water, speeding up the rate of extraction.

The second thing the grind size determines is the flow rate for certain methods of coffee brewing, such as pour-over, which, in turn, affects extraction levels. The smaller the coffee particles, the more slowly water can seep down through them; the larger the coffee particles, the faster. If you imagine two pipes, one of which is packed with sand and one that’s packed with marbles, and you poured water through each, the water would pass much more quickly through the marbles than the sand, given all the empty space around them. With coffee, the water traveling more slowly through the finer grounds has more time to extract coffee molecules, while the water racing through a coarsely ground coffee will have less time.

Exactly how coarse or fine to grind coffee depends on a complex set of factors, including the batch size, the brewing method, and the coffee beans themselves. It’s a moving target and therefore takes some practice to begin to understand how to use grind size to improve your coffee.

As you are probably starting to see, given how grind size can determine surface area and flow rate, and thus extraction, a grinder that offers a wide range of grind sizes and produces a uniformly sized result at each grind setting is desirable. The idea is that if a grinder produces coffee grounds that have too much variance in size for any given grind setting, results become increasingly difficult to control. A setting that’s meant to produce a medium grind but instead gives that medium grind littered with fine powder and too-big chunks, may under- or overextract, or both. At least, that’s the theory.

Exactly how uniform coffee grounds need to be is open for debate, and it’s something professionals in the coffee industry continue to explore. If we can say one thing with certainty, it’s that we want a grinder that helps us produce a cup of coffee that we consider enjoyable and delicious. As Nick Cho of Wrecking Ball Coffee pointed out in a conversation I had with him a few years ago: The challenge is finding agreement about what that means.

Cho told me he’d done a taste test some years before our conversation, and that even coffee professionals were all over the place in terms of their preferences. “No one has to learn to like strawberries,” Cho said at the time. “Whereas with coffee or beer, the things that contain bitterness, it’s an acquired taste—so what kind of taste you acquire is everything.”

Before diving into my review of coffee grinders, I decided to explore this question a little more deeply.

Do You Really Need a Good Burr Grinder?

My first grinder tests go back a couple of years. I wanted to get some data, and my initial results left the question unresolved. In those tests, I pitted one of our favorite blade grinders (technically, it’s a spice grinder, but lots of people use them for coffee) against an inexpensive burr grinder (the Cuisinart DBM-8) and a higher-end burr grinder (Breville’s Smart Grinder Pro). I used a Clever coffee dripper in those tests, which was a brewer that made it easier to control some key variables. All samples were tasted blind by my colleagues.

In each of those tests, tasters preferred the coffee made by the higher-end grinder more than the other two, and the blade grinder came in last for most people, but we were all surprised to find that the differences weren’t particularly striking—certainly not different enough to support the common recommendation that most home-brewed coffee drinkers should pay for a really good burr grinder. Yes, there was a difference, but if we didn’t have the benefit of side-by-side tastings, we weren’t sure we’d have been able to easily tell them apart.

Fast-forward to this year, when I finally decided to return to this question while working on this review. I headed over to the Joe Coffee Company Pro Shop, where Christopher Malarick, who also worked with us on our automatic coffee brewer review, helped me run a new round of tests.

This time we assembled a tasting panel that included two professionals (Malarick and a Joe Coffee colleague) along with four civilian tasters who represented a range of coffee-drinking expertise and preferences.

For this test, we used four different grinders, each representing a different class. A Krups blade spice grinder represented the type of grinder usually frowned upon by professionals; a Krups GX5000 burr grinder, which retails for about 30, represented the absolute cheapest of burr grinder options; the Baratza Virtuoso was our representative high-end home grinder; and a pro-level Mahlkonig EK-43, which is famed for its consistent grind quality and sells for nearly 3,000, acted as the crème de la crème against which all the other grinders were compared.

Malarick did all the brewing on a Kalita Wave pour-over brewer, which is prized for its consistency, and we tasted all samples blind.

We ran this test two times, using two different roast profiles. The first one was a Joe’s blend called The Waverly, which combines Peruvian and Colombian beans with a medium roast profile. The second was a very, very dark Italian roast from Starbucks. The results shed more light on the complexity of how drinkers perceive coffee and how the grinder can affect that perception.

With the medium roasted beans, the tallied results put the grinders more or less in order of quality, with the EK-43 in first place and the blade grinder in last place. But not everyone agreed. One of the pros rated the blade grinder in the middle of the pack, and the other pro, who admitted later he wasn’t a huge fan of the Waverly blend, had an inverted list, with the blade grinder his favorite and the EK-43 his least favorite. In light of his opinion on the blend, this starts to make sense: the EK-43 created the truest expression of the coffee, which he didn’t love, while the blade grinder produced a less clear expression of the beans, which worked for him—the less he could taste of the coffee’s nuances, the better.

Among the civilian tasters, one picked the two cheapest grinders—the blade grinder and budget Krups burr grinder—as his favorites and the coffees from the higher-end grinders as his least favorite. His tasting notes seem to indicate that he wasn’t the biggest fan of this coffee either, and so, perhaps like the pro, he valued the grinders that obscured the coffee’s full flavor. The remaining civilians ranked the coffees as one might expect, with the better grinders tending to get higher scores.

But things took an interesting twist when we switched to the dark Starbucks roast. Rankings became scattered, with no clear pattern, except that the EK-43 got consistently bad scores. A couple tasters had a hard time ranking the coffees at all, handing out ties and noting that it was difficult to tell the samples apart. Others did their best to rank the results, but all agreed afterward that the differences were incredibly difficult to notice, even in side-by-side tastings. The oft-maligned blade grinder came out toward the top on a couple tasting sheets, including in both of the professionals’ assessments (they each ranked it the second-best tasting coffee of the bunch).

What does this tell us? Mostly, it tells us that the preferences of the individual taster matter a lot and that the coffee itself has a significant role in determining whether a grinder’s uniformity of grind matters much or not. The darker the roast, the less the grinder’s quality seems to matter. If anything, the uniformly sized grounds produced by the better grinders seemed to be a bad thing for the dark roast, bringing some of the harsher charred flavors to the fore.

This makes some sense when you consider that the more deeply a coffee is roasted, the more it loses its original flavors and takes on a more generic roasty profile. A dark roast is not unlike oak in wine or hops in beer—it’s an equalizer of sorts, erasing some of a bean’s natural flavor, covering up flaws, and pushing the product’s overall flavor in one very particular direction. That’s not necessarily a bad thing, but it can lessen the effect that grind uniformity, and therefore the grinder itself, can have.

The lesson here is that coffee drinkers need to know what their preferences are in order to make an informed decision about which grinder to buy.

Do they prefer medium and lighter roasts that try to preserve the original character of the bean? Do they drink the coffee black instead of adding ingredients like milk and sugar, which can mask flavors and soften the harsh edges of darkly roasted beans? Or do they like a dark roast, maybe with a splash of cream or a bit of sweetener? Answers to these questions will determine which burr grinder is right for them or even if a blade grinder will suffice.

The Testing

The above taste tests were very helpful in constructing a more complex picture of just how much and when a grinder truly matters. With that information helping to inform us, the next step was to analyze each grinder, looking at both the range of grind sizes each machine offered as well as how uniform the grinds were. We could then see how each grinder related to the others in terms of quality and price and make recommendations.

Test 1: Grind Screening

To determine grind uniformity and range, we ran each grinder at its coarsest, middle, and finest settings and analyzed the results. We used a Kruve sifter system to sort and analyze the grinds.

Before running these tests, I called up Steve Rhinehart of Prima Coffee Equipment in Louisville, Kentucky, to get some of his wisdom on grinders. According to Rhinehart, ideal grind sizes fall roughly as follows: 1,000 microns and larger for French press; 600 to 800 microns are the most common sizes for most other home-brewing methods like pour-over; grinds for AeroPress and moka pots often fall in the 400 to 600 micron range; espresso is usually around 300 to 400 microns. Anything ground smaller than that is referred to as “fines” and is considered undesirable, as it will overextract quickly and clog filters.

Those numbers line up with the filter screen sizes Malarick used to separate our samples into groupings, cutting each into three groups: smaller than 400 microns (essentially an espresso grind and fines); between 400 and 1,000 microns (the range most useful for home coffee-making methods); and larger than 1,000 microns, for French press and such.

Since the 400 to 1,000 microns is still quite a large range, we did a visual assessment to see roughly how consistent and how large the grinds seemed to be within that range.

Test 2: Taste Tests

In addition to all of the rounds of taste tests described above, we also ran our finalists through more rigorous tests. This included grinding several varieties of beans from different roasters and brewing coffee dozens of times, and using different brewing methods to get used to the machines to develop a sense of how easy they are to dial in our preferences and otherwise assess real-world results.

Test 3: Design Quality Assessment

Throughout testing, we examined the build quality of each machine, its ease of use, loudness, and other design factors and weighed those in our final decisions of which grinders to recommend.

Test 4: Quick Espresso Test

This review deliberately did not take a close look at espresso. As just about any professional barista will tell you, home grinders at this price point are generally not considered up to par for pulling good espresso shots, largely due to a lack of fine-tune settings to truly dial a shot in.

Unfortunately, espresso is a more expensive brewing method to get into at home, and grinders that are made for it tend to cost quite a bit more, starting at several hundred dollars and climbing up into the thousands. Probably the most affordable and well-regarded espresso grinder for home use is the Sette series made by Baratza.

Still, after we’d narrowed the field of grinders in this test down to the final set, I thought it’d be fun to at least try them for espresso, and the folks at Joe were kind enough to humor me. We didn’t try to pull shots with any but the top performers—the Baratza Virtuoso and the Breville Smart Grinder—starting each at its finest setting just to see what would happen.

What we found is that both of those grinders are capable of grinding fine enough for an espresso shot—the finest settings were, in fact, too fine, clogging the portafilter and preventing the water from flowing through properly.

Malarick was concerned that the Virtuoso didn’t have small enough steps between grind settings to allow him to adequately dial in that shot, but the Breville, which leans fine and devotes about a third of its grind settings to espresso-level fineness, stood a better chance. He adjusted the Breville’s grind and pulled a second shot with it, getting it closer to his goal. He still wasn’t happy with it, but I didn’t think it tasted too bad.

Overall, it was clear that none of these grinders could really pass muster with a professional barista for pulling espresso shots, but for a home user who’s less concerned with pro-level perfection, the Breville can work.

How We Chose Our Winners

Our recommendations considered price as well as quality, keeping in mind the ideal user in each case. Remember, the “best” grinders aren’t necessarily the best for all coffee drinkers.

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