Choosing The Right Grinding Wheel. Sanding wheel for grinder
GUIDE TO FLAP DISCS
Many manufacturing applications benefit from the use of a flap disc. In the lineup of surface conditioning tools like cutting and grinding wheels, how are flap discs distinctive?
Flap discs, also known colloquially as flapper wheels, have a design suited for right-angle grinder applications. They provide aggressive stock removal or precise blending and finishing depending on the operator’s needs. They offer exceptional versatility, maneuverability and lower vibration and noise levels than grinding wheels.
Flap discs are excellent choices for many applications because they allow the operator to perform grinding and finishing in one efficient time-saving, cost-lowering step. They grind like hard grinding wheels but are easier to control so you reduce the risk of gouging the workpiece, and they remain usable even after an area of abrasive wears out because new abrasive is exposed. They also tend to have a softer feel than grinding wheels, and they reduce the risk of removing too much material from the workpiece with overaggressive grinding.
When a facility is choosing angle grinder flap discs, it’s essential to consider factors like shape, material, density and abrasive grain type and size. This guide to flap discs discusses these characteristics and what they mean for flap disc performance.
CHOOSING FLAP DISC SHAPE
In discussing flap discs’ shape, we’ll first want to consider their structure and composition.
Unlike a standard grinding wheel, which consists of a uniform grinding surface made of abrasive grains bonded in place, a flap disc consists of a ring of overlapping flaps. These flaps hold coated abrasive grains — the same grains used in bonded-abrasive cutting and grinding wheels — that can grind and shape a workpiece during fabrication or blend and finish a weld.
Where cutting and grinding discs often have a fiberglass structure, in flap discs the grains adhere to a backing cloth often made of cotton, polyester or a blend. The abrasive cloth is cut into smaller strips and then layer the strips so they overlap one another to form the flap disc. A rigid back plating provides stability and support.
The two most common types of flap discs are flat discs and conical discs:
- Flat discs: Flat flap discs, also known as type 27 flap discs, typically grind best at shallower angles between 0 and 15 degrees. They are optimal for smooth finishing and blending on flat surfaces, and they can handle slight contours.
- Conical discs: Conical flap discs, also known as type 29 flap discs, have a saucer-shaped grinding surface rather than a straight one. They typically grind best at angles between 15 and 35 degrees. They enable aggressive stock removal by maximizing surface contact on flat surfaces.
In general, operators should choose conical flap discs for initial high-volume grinding and flat flap discs for precision refinements.
A few specialty shapes and styles are also available:
- Trimmable discs: Trimmable flap discs differ from other types because they contain a trimmable composite backing that allows the operator to increase flap overhang. When used as intended, these discs offer flexibility and versatility needed for hard-to-reach areas such as fillet welds and irregular shapes. The backings also prevent unwanted marking of the workpiece.
- Aluminum-backed discs: Flap discs with aluminum backs contain a sturdy, permanent aluminum backing. This backing provides rigorous support in high-stress, heavy-duty applications such as pipeline fabrication.
- Mini discs: Mini flap discs are significantly smaller than their standard counterparts, only about 2 or 3 inches in diameter. Their compact size makes them ideal for working in tight spaces and grinding hard-to-reach areas on the workpiece. A smaller, 2-inch mini disc can often effectively replace a blending disc as well. These discs contain a composite backing that provides standard support for a range of applications.
- Angled discs: Angled flap discs have curved flaps that wrap around the edge of the backing plate, facilitating extensive flap-to-metal contact, enhancing operator control and allowing for a wider range of grinding angles. The curved flaps give these discs the contouring capabilities necessary for fillet welds and allow for access hard-to-reach areas for T-joint grinding. They offer the same robust grinding performance on flat surfaces.
Flap discs also come in a range of sizes, generally from about 4 to 7 inches in diameter, with the mini discs smaller still. Smaller discs are designed for use on die grinders to provide smooth grinding and enhanced conformability in tight areas. will rotate more quickly and provide a faster cut rate, whereas larger discs will rotate more slowly. Larger-diameter wheels contain more abrasive, however, so with the right care, because of their size will cover larger areas and will last longer and provide a higher rate of stock removal over the life of the disc.
Flap disc shapes also differ in the width of the individual flaps. The industry standard for these flaps is about 25 millimeters, and some flap discs, including Weiler Abrasives’ Tiger Paw high density and Big Cat discs, contain 30-millimeter flaps instead. The larger flaps provide a more expansive surface area for applications that require aggressive, high-volume grinding.
CHOOSING FLAP DISC MATERIAL
We’ll discuss the abrasive grains and their composition a little further on. In this section, let’s delve into the different backings a flap disc might have. Common backing materials for flap discs include phenolic resin, aluminum and composite.
- Phenolic: Phenolic is a substance formed through the application of heat and pressure to alternating layers of resin and materials like glass-based fabric. Phenolic is lightweight and wear-resistant, and it is useful for preventing the flap disc and its backing from scratching the workpiece.
- Aluminum: Aluminum backing provides sturdiness and stability for the flap disc in heavy-duty applications. Its rigid support makes it ideal for aggressive grinding applications such as cleaning pits out of bevels, and the smooth aluminum won’t catch on the bevel. Aluminum also offers the benefit of recyclability.
- Composite: Trimmable composite backing is ideal for preventing marking of the workpiece. Because the trimmable backing allows for small adjustments to the disc’s size and shape, composite allows greater access to hard-to-reach areas of the workpiece.
CHOOSING ABRASIVE FLAP DENSITY
High-density flap discs contain more abrasive cloth material than standard flap discs, so they are thicker and more forgiving. Because of their density, they can conform to irregular surfaces in a way that standard flap discs cannot, so they provide greater control and performance with nonstandard shapes and materials. They may be either type 27 discs or type 29 discs.
- Type 27: Type 27 high-density flap discs have the same straight profile associated with flat flap discs, and they contain added thickness. They are ideal for grinding at angles between 0 and 15 degrees. They conform easily to irregular surfaces and provide smooth blending, grinding and finishing on flat surfaces as well.
- Type 29: Type 29 high-density flap discs have an angled profile associated with conical flap discs. They are ideal for grinding at angles between 15 and 35 degrees. Their density and angled design make them ideal for operators looking for aggressive stock removal while also conforming to irregular workpiece surfaces.
When should a company choose high-density flap discs for its applications? Generally, standard-density flap discs are excellent choices for aggressive stock removal and demanding industrial applications. High-density flap discs, on the other hand, are best suited for curved or uneven surfaces, or for blending and finishing rather than heavy stock removal.
If a long lifespan is a high priority, operators may want to choose high-density flap discs over standard flap discs. Because they contain more material, high-density flap discs last up to 40% longer than standard flap discs under the right operating conditions. They are versatile enough to use on both irregular and flat surfaces, so prioritizing disc life won’t mean compromising performance on flat workpieces.
CHOOSING ABRASIVE GRIT MATERIAL
The choice of material for a flap disc usually depends on the application and workpiece material in question. Below are a few common types of flap disc materials:
If you are looking for maximum performance in a flap disc, Ceramic is the best option. The ceramic grains micro-fracture as they grind, constantly exposing sharp edges and maintaining a high cut rate for the life of the disc. It is ideal for workpieces made from standard steel, tool steel, armored steel, titanium, Inconel high-nickel alloys, stainless steel and aluminum, and it performs exceptionally well on hard-to-grind metals.
In combination with a top coat, ceramic alumina provides a fast cut rate, and a cooler grinding temperature to help protect valuable, heat-sensitive components and prevent heat discoloration on the workpiece. The top coat also helps prevent loading — the accumulation of bits of workpiece material on the flap disc — with soft alloys. Our Tiger Ceramic option is top coated and is also contaminant-free so it will perform exceptionally well on stainless steel.
A flap disc made from 100% zirconia alumina allows for aggressive stock removal and high-performance edge grinding. Zirconia alumina is self-sharpening, and it holds up exceptionally well under high temperatures and pressures. With proper use and maintenance, it provides a Rapid cut and long lifespan. It is ideal for workpieces made from cast iron, carbon steel, structural steel and stainless steel. If you are looking for a 100% zirconia alumina our Tiger Paw is an excellent choice.
CERAMIC ALUMINA/ZIRCONIA ALUMINA BLEND
A blend of ceramic alumina and zirconia alumina provides fast grinding, reliable performance and a long disc life. This grain combination grinds with less effort than many other. Our Tiger X flap disc leverages a contaminant-free blend is ideal for flat surface grinding, particularly on workpieces made from structural steel, carbon steel, stainless steel and cast iron.
A disc made from aluminum oxide has a hard, durable grain and a strong initial cut rate, and it offers fast stock removal and consistent performance. Aluminum oxide is ideal for workpieces made of materials such as steel and cast iron, as well as for all-purpose use. It is not shelf-sharpening, however — its single crystals will dull during use. Overall, it provides a blend of performance and value.
CHOOSING ABRASIVE GRIT SIZE FOR YOUR APPLICATION
Flap disc grains come in an array of sizes, just as sandpaper grains do. The abrasive grains for flap discs typically range from about 36 to 120, with smaller numbers indicating larger, coarser grit and larger numbers indicating smaller, finer grit.
In general, flap discs require coarser grit for initial workpiece shaping and stock removal and finer grit for refinements such as blending, finishing and repairs. Below is a breakdown of what some of these numbers signify for flap disc performance:
- Heavy stock removal: Larger abrasive grit in the 36-to-40 range facilitates heavy-duty operations like heavy stock removal from workpieces.
- Chamfering and edge beveling: Larger abrasive grit in the slightly more expansive 36-to-60 range facilitates edge work such as chamfering and edge beveling.
- Weld grinding and blending: Abrasive grit ranging in size from about 40 to 60 is suitable for applications like weld grinding and blending.
- Deburring and deflashing: 60 grit abrasive grain is ideal for deburring and deflashing work.
- Rust removal and blending: Abrasive grit in the more expansive range from 60 to 80 is optimal for finer work like rust removal and blending.
- Cleaning and finishing: Finer abrasive grit ranging in size from about 80 to 120 is well suited to more delicate refining applications such as cleaning and finishing.
COMMON INDUSTRIES FOR FLAP DISCS
So far, we’ve discussed the way different grain sizes enhance flap disc performance, with coarser grains ideal for initial stock removal and finer grains better suited for finishing — an operation that requires a flap disc for grinding welds may choose a large to medium grain size, for instance. We’ve discussed the effect of disc diameters on speed and surface area. We’ve explored how various abrasive grains work best for different applications.
Now let’s examine how to use flap discs in different industries:
- Construction: In construction applications, 5- or 6-inch flap discs are often advantageous. A 5- or 6-inch disc is lightweight and portable enough for use in construction while still providing the performance necessary for the jobsite.
- General metal fabrication: Flap discs are indispensable for general metal fabrication. Their versatility and adaptability to a range of grinding applications, from stock removal and deburring to cleaning and finishing, make them superior tools for numerous metal workpieces.
- Pipeline development: Tiger Aluminum Back flap discs are the benchmark for the pipeline industry, providing rigid support for maximum aggression. These wheels are ideal for removing heavy pitting and resists rolling the bevel ends prior to welding. The aluminum backing also prevents the disc from catching on the bevel when grinding.
- Aluminum / Shipbuilding: In industries like trailer fabrication and shipbuilding, aluminum is often the metal of choice. Because aluminum is a soft metal it tends to load so a flap disc with a top coat is a must to prevent the disc from gumming up. In addition to Tiger Ceramic, we now offer Tiger Aluminum which also features a top coat. Tiger Aluminum offers a unique paired flap design for high performance grinding for aluminum at an exceptional value.
PARTNER WITH WEILER ABRASIVES FOR HIGH-QUALITY FLAP DISCS
To gain quality surface conditioning solutions for your operations, work with Weiler Abrasives. Our experienced, knowledgeable teams can help you find the best flap discs for a grinder. Whether you need a flap disc for grinding steel, aluminum or cast iron, and whether you need a 2-inch mini disc for blending or a rugged 6-inch ceramic disc for your most demanding challenges, you’ll find a product that works for your needs.
The benefits of a partnership with Weiler Abrasives extend far beyond your initial purchase. We offer a comprehensive Value Package designed to promote safety and support your flap disc use with insight and advice. The Value Package incorporates safety training to protect your employees as they use our tools and customized field support to answer your questions and help you get the most out of your flap disc.
Contact us today to learn about our flap discs’ benefits for your angle grinders.
Choosing The Right Grinding Wheel
The grinding wheel is a cutting tool. It’s an abrasive cutting tool.
In a grinding wheel, the abrasive performs the same function as the teeth in a saw. But unlike a saw, which has teeth only on its edge, the grinding wheel has abrasive grains distributed throughout the wheel. Thousands of these hard, tough grains move against the workpiece to cut away tiny chips of material.
Abrasive suppliers offer a wide array of products for a variety of grinding applications in metalworking. Choosing the wrong product can cost the shop time and money. This article presents some of the fundamentals of selecting the best grinding wheel for the job.
Abrasives — Grits and Grains
Grinding wheels and other bonded abrasives have two major components: the abrasive grains that do the actual cutting and the bond that holds the grains together and supports them while they cut. The percentages of grain and bond and their spacing in the wheel determine the wheel’s structure.
The particular abrasive used in a wheel is chosen based on the way it will interact with the work material. The ideal abrasive has the ability to stay sharp with minimal point dulling. When dulling begins, the abrasive fractures, creating new cutting points.
Each abrasive type is unique with distinct properties for hardness, strength, fracture toughness and resistance to impact.
Aluminum oxide is the most common abrasive used in grinding wheels. It is usually the abrasive chosen for grinding carbon steel, alloy steel, high speed steel, annealed malleable iron, wrought iron as well as bronzes and similar metals. There are many different types of aluminum oxide abrasives, each specially made and blended for particular types of grinding jobs. Each abrasive type carries its own designation, usually a combination of a letter and a number. These designations vary by manufacturer.
Zirconia alumina is another family of abrasives, each one made from a different percentage of aluminum oxide and zirconium oxide. The combination results in a tough, durable abrasive that works well in rough grinding applications, such as cut-off operations, on a broad range of steels and steel alloys. As with aluminum oxide, there are several different types of zirconia alumina from which to choose.
Silicon carbide is an abrasive used for grinding gray iron, chilled iron, brass, soft bronze and aluminum, as well as stone, rubber and other nonferrous materials.
Ceramic aluminum oxide is another major development in abrasives. This is a high-purity grain manufactured in a gel sintering process. The result is an abrasive with the ability to fracture at a controlled rate at the submicron level, constantly creating thousands of new cutting points. This abrasive is exceptionally hard and strong. It is primarily used for precision grinding in demanding applications on steels and alloys that are the most difficult to grind. The abrasive is normally blended in various percentages with other abrasives to optimize its performance for different applications and materials.
Once the grain is known, the next question relates to grit size. Every grinding wheel has a number designating this characteristic. Grit size is the size of individual abrasive grains in the wheel. It corresponds to the number of openings per linear inch in the final screen size used to size the grain. In other words, higher numbers translate to smaller openings in the screen the grains pass through. Lower numbers (such as 10, 16 or 24) denote a wheel with coarse grain. The coarser the grain, the larger the size of the material removed. Coarse grains are used for Rapid stock removal where finish is not important. Higher numbers (such as 70, 100 and 180) are fine grit wheels. They are suitable for imparting fine finishes, for small areas of contact and for use with hard, brittle materials.
To allow the abrasive in the wheel to cut efficiently, the wheel must contain the proper bond. The bond is the material that holds the abrasive grains together so they can cut effectively. The bond must also wear away as the abrasive grains wear and are expelled so new, sharp grains are exposed.
There are three principal types of bonds used in conventional grinding wheels. Each type is capable of giving distinct characteristics to the grinding action of the wheel. The type of bond selected depends on such factors as the wheel operating speed, the type of grinding operation, the precision required and the material to be ground.
Most grinding wheels are made with vitrified bonds, which consist of a mixture of carefully selected clays. At the high temperatures produced in the kilns where grinding wheels are made, the clays and the abrasive grain fuse into a molten glass condition. During cooling, the glass forms a span that attaches each grain to its neighbor and supports the grains while they grind.
Grinding wheels made with vitrified bonds are very rigid, strong and porous. They remove stock material at high rates and grind to precise requirements. They are not affected by water, acid, oils or variations in temperature.
Vitrified bonds are very hard, but at the same time, they are brittle like glass. These bonds are broken down by the pressure of grinding.
Some bonds are made of organic substances. These bonds soften under the heat of grinding. The most common organic bond type is the resinoid bond, which is made from synthetic resin. Wheels with resinoid bonds are good choices for applications that require Rapid stock removal, as well as those where better finishes are needed. They are designed to operate at higher speeds, and they are often used for wheels in fabrication shops, foundries, billet shops and for saw sharpening and gumming.
Another type of organic bond is rubber. Wheels made with rubber bonds offer a smooth grinding action. Rubber bonds are often found in wheels used where a high quality of finish is required, such as ball bearing and roller bearing races. They are also frequently used for cut-off wheels where burr and burn must be held to a minimum.
The strength of a bond is designated in the grade of the grinding wheel. The bond is said to have a hard grade if the spans between each abrasive grain are very strong and retain the grains well against the grinding forces tending to pry them loose. A wheel is said to have a soft grade if only a small force is needed to release the grains. It is the relative amount of bond in the wheel that determines its grade or hardness.
Hard-grade wheels are used for longer wheel life, for jobs on high-horsepower machines and for jobs with small or narrow areas of contact. Soft grade wheels are used for Rapid stock removal, for jobs with large areas of contact, and for hard materials such as tool steels and carbides.
The wheel itself comes in a variety of shapes. The product typically pictured when one thinks of a grinding wheel is the straight wheel. The grinding face— the part of the wheel that addresses the work — is on the periphery of a straight wheel. A common variation of the straight wheel design is the recessed wheel, so called because the center of the wheel is recessed to allow it to fit on a machine spindle flange assembly.
On some wheels, the cutting face is on the side of the wheel. These wheels are usually named for their distinctive shapes, as in cylinder wheels, cup wheels and dish wheels. Sometimes bonded abrasive sections of various shapes are assembled to form a continuous or intermittent side grinding wheel. These products are called segments. Wheels with cutting faces on their sides are often used to grind the teeth of cutting tools and other hard-to-reach surfaces.
Mounted wheels are small grinding wheels with special shapes, such as cones or plugs, that are permanently mounted on a steel mandrel. They are used for a variety of off-hand and precision internal grinding jobs.
Grinding wheels are generally labeled with a maximum safe operating speed. Don’t exceed this speed limit. The safest course is not even to mount a given wheel on any grinder fast enough to exceed this limit.
These diamond metal bond wheels offer superior performance in round tool grinding.
Tying It All Together
A number of factors must be considered in order to select the best grinding wheel for the job at hand. The first consideration is the material to be ground. This determines the kind of abrasive you will need in the wheel. For example, aluminum oxide or zirconia alumina should be used for grinding steels and steel alloys. For grinding cast iron, nonferrous metals and non-=metallic materials, select a silicon carbide abrasive.
Hard, brittle materials generally require a wheel with a fine grit size and a softer grade. Hard materials resist the penetration of abrasive grains and cause them to dull quickly. Therefore, the combination of finer grit and softer grade lets abrasive grains break away as they become dull, exposing fresh, sharp cutting points. On the other hand, wheels with the coarse grit and hard grade should be chosen for materials that are soft, ductile and easily penetrated.
The amount of stock to be removed is also a consideration. Coarser grits give Rapid stock removal since they are capable of greater penetration and heavier cuts. However, if the work material is hard to penetrate, a slightly finer grit wheel will cut faster since there are more cutting points to do the work.
Wheels with vitrified bonds provide fast cutting. Resin, rubber or shellac bonds should be chosen if a smaller amount of stock is to be removed, or if the finish requirements are higher.
Another factor that affects the choice of wheel bond is the wheel speed in operation. Usually vitrified wheels are used at speeds less than 6,500 surface feet per minute. At higher speeds, the vitrified bond may break. Organic bond wheels are generally the choice between 6,500 and 9,500 surface feet per minute. Working at higher speeds usually requires specially designed wheels for high speed grinding.
In any case, do not exceed the safe operating speed shown on the wheel or its blotter. This might be specified in either rpm or sfm.
The next factor to consider is the area of grinding contact between the wheel and the workpiece. For a broad area of contact, use a wheel with coarser grit and softer grade. This ensures a free, cool cutting action under the heavier load imposed by the size of the surface to be ground. Smaller areas of grinding contact require wheels with finer grits and harder grades to withstand the greater unit pressure.
Next, consider the severity of the grinding action. This is defined as the pressure under which the grinding wheel and the workpiece are brought and held together. Some abrasives have been designed to withstand severe grinding conditions when grinding steel and steel alloys.
Grinding machine horsepower must also be considered. In general, harder grade wheels should be used on machines with higher horsepower. If horsepower is less than wheel diameter, a softer grade wheel should be used. If horsepower is greater than wheel diameter, choose a harder grade wheel.
Care And Feeding
Grinding wheels must be handled, mounted and used with the right amount of precaution and protection.
They should always be stored so they are protected from banging and gouging. The storage room should not be subjected to extreme variations in temperature and humidity because these can damage the bonds in some wheels.
Immediately after unpacking, all new wheels should be closely inspected to be sure they have not been damaged in transit. All used wheels returned to the storage room should also be inspected.
Wheels should be handled carefully to avoid dropping and bumping, since this may lead to damage or cracks. Wheels should be carried to the job, not rolled. If the wheel is too heavy to be carried safely by hand, use a hand truck, wagon or forklift truck with cushioning provided to avoid damage.
Before mounting a vitrified wheel, ring test it as explained in the American National Standards Institute’s B7.1 Safety Code for the Use, Care and Protection of Grinding Wheels. The ring test is designed to detect any cracks in a wheel. Never use a cracked wheel.
A wise precaution is to be sure the spindle rpm of the machine you’re using doesn’t exceed the maximum safe speed of the grinding wheel.
Always use a wheel with a center hole size that fits snugly yet freely on the spindle without forcing it. Never attempt to alter the center hole. Use a matched pair of clean, recessed flanges at least one-third the diameter of the wheel. Flange bearing surfaces must be flat and free of any burrs or dirt buildup.
Tighten the spindle nut only enough to hold the wheel firmly without over-tightening. If mounting a directional wheel, look for the arrow marked on the wheel itself and be sure it points in the direction of spindle rotation.
Always make sure that all wheel and machine guards are in place, and that all covers are tightly closed before operating the machine. After the wheel is securely mounted and the guards are in place, turn on the machine, step back out of the way and let it run for at least one minute at operating speed before starting to grind.
Grind only on the face of a straight wheel. Grind only on the side of a cylinder, cup or segment wheel. Make grinding contact gently, without bumping or gouging. Never force grinding so that the motor slows noticeably or the work gets hot. The machine ampmeter can be a good indicator of correct performance.
If a wheel breaks during use, make a careful inspection of the machine to be sure that protective hoods and guards have not been damaged. Also, check the flanges, spindle and mounting nuts to be sure they are not bent, sprung or otherwise damaged.
The grinding wheel is one component in an engineered system consisting of wheel, machine tool, work material and operational factors. Each factor affects all the others. Accordingly, the shop that wants to optimize grinding performance will choose the grinding wheel best suited to all of these other components of the process.
About the author: Joe Sullivan was a senior product manager for Norton Company, Worcester, Massachusetts.
What Are Superabrasives?
Superabrasives make up a special category of bonded abrasives designed for grinding the hardest, most challenging work materials.
Because carbides, high speed steels, PCD, PCBN, ceramics and some other materials used to make cutting tools can be nearly as hard as conventional abrasives, the job of sharpening them falls to a special class of abrasives-diamond and the CBN, the superabrasives.
These materials offer extreme hardness, but they are more expensive than conventional abrasives (silicon carbide and aluminum oxide). Therefore, superabrasive grinding wheels have a different construction than conventional abrasive wheels. Where a conventional abrasive product is made up of abrasive all the way through, superabrasive wheels have abrasive on the cutting edge of the wheel that is bonded to a core material, which forms the shape of the wheel and contributes to the grinding action.
Superabrasive wheels are supplied in the same standard grit range as conventional wheels (typically 46 through 2,000 grit). Like other types of wheels, they can be made in a range of grades and concentrations (the amount of diamond in the bond) to fit the operation.
There are four types of bond used in superabrasive wheels. Resinoid bond wheels are exceptionally fast and cool cutting. They are well-suited to sharpening multi-tooth cutters and reamers, and for all precision grinding operations. Resin is the “workhorse” bond, most commonly used and most forgiving. Vitrified bond wheels combine fast cutting with a resistance to wear. They are often used in high-volume production operations. Metal bond wheels are used for grinding and cutting nonmetallic materials, such as stone, reinforced plastics and semiconductor materials that cannot be machined by other cutting tools. Single-layer plated wheels are used when the operation requires both fast stock removal and the generation of a complex form.
Grinding Wheel vs Flap Disc vs Sanding Disc: What Is the Difference?
When you are using your angle grinder for DIY projects, one of the most important considerations is which type of attachment you are going to use. Grinding wheels, flap discs and sanding discs are among the most common grinder attachments yet they are used for very different types of projects.
Typical uses of a grinding wheel include removal of material while a flap disc is the first choice for abrading metal. If you need to sand wood or other material with your angle grinder, a sanding disc is the right attachment to use, although the results would mostly be second to those of an actual sander.
Read on to learn the details of each of these grinder attachments. Read this article on how to use a grinder to learn more about cutting tiles and sanding wood or steel.
What Are the Different Uses of Grinding Wheels, Flap Discs and Sanding Discs?
Although all these types of attachment are for use with an angle grinder, the outcomes and the materials they can deal with are different. The following table summarizes the differences in their use.
|Grinding wheel||Flap disc||Sanding disc|
|Processing and results||Surface removal, trimming and cleaning; Saw-type wheels produce cuts on different material||Abrasion and Finishing of surfaces||Sanding and finishing surfaces|
|Material||Removing metal fast; MIG welding; wood; stone and concrete||Metal||Wood; metal; concrete, stone and other material (special discs needed)|
|Typical uses||Trimming surfaces quickly; Cutting workpieces (saw-type wheels)||Shaping metal; A slower, less spark-producing alternative to grinding wheels for weld deposits and slag removal||Sanding and finishing surfaces if no advanced smoothness is required (otherwise, a sander would be the better choice)|
|Price level (per piece)||Check on Amazon||Check on Amazon||Check on Amazon|
Move forward to the next sections to learn more about the characteristics of each of these attachment types as well as practical tips for their uses.
Grinding Wheels come in a variety of sizes and thicknesses. Make sure the wheels you purchase are the correct size so they fit into your angle grinder’s guard. They should also be about a quarter of an inch thick. Any thinner than this and you may be looking at a cutting disk instead of a grinding disk.
What Are Grinding Wheels Used For?
A standard grinding wheel is designed for quickly removing metal. Use it for preparing metal for MIG welding, clean and trim down old welds and removing welding slag. They are available in different sized Grits just like sandpaper. Lower numbered grits are coarser and remove metal quicker while higher grits are for finishing work, cleaning and polishing. A higher grit grinding wheel may take a bit longer to finish the job than a lower sized one but it will be safer and more comfortable as fewer large sparks will be produced.
Low grit grinding wheels produce large and very hot sparks. If these land on your skin, they are mildly uncomfortable, rather like a small bee sting. However, they are hot enough to melt some clothing, especially man-made fibers and, if landing on glass, they can embed into the glass. Eye protection or a face shield should always be used.
Over time, grinding disks will gradually wear down in size and they should be replaced appropriately. If a disk is misused or jumps during use, it may become damaged and should be immediately replaced for safety. Cheaper disks can become damaged then fail completely spreading flying pieces of disc into the air. This can cause damage and be very dangerous if safety equipment is not being worn.
Special grinder disks with chain saw type blades are available for specifically cutting and shaping of wood. There are also available grinder disks with teeth on the outer edge which are also intended for woodworking.
Flap Disks are abrasive disks made from small flaps of overlapping abrasive covered cloth formed in the shape of a wheel. Flap disks are more efficient in their use than using a flat abrasive paper in that flap disks wear from the outside edge in distributing the wear evenly across the entire disk. The length of each flap can be worn down completely before the disk needs to be replaced so the wheel is useful as the flaps erode, unlike a flat abrasive sheet which must be discarded even if only a small part of the sheet is eroded away. Flap disks last up to 25 times longer than fiber disks
The advantages of flap disks during use are that each separate flap attacks the workpiece at a very slightly different angle which also varies with the angle of the grinder. This avoids the common issues with flat abrasive paper that can easily produce identical repeated scratches in the work.
What Are Flap Discs Used For?
They are used to shape and contour metal and can be used as an alternative to grinding wheels for removing weld deposits and slag. They remove metal slower and produce smaller sparks than grinding wheels. Flap disks are less robust than grinding wheels and can be damaged easily if care is not taken. Because they consist of only pieces of abrasive covered fabric glued to a solid backing by resin, there are fewer pieces that may become damaged and fly off so are generally safer than grinding wheels. They are lighter than grinding wheels so produce less vibration and are easier to operate.
Sanding discs with different grits.Check on Amazon.
Angle grinders can be used for sanding both wood and metal but also other types of material. When you need to sand a lot of wood away, a sanding disk attachment is ideal. However, for wood, angle grinder rotary sanding does not produce such a good finish as is obtained with a random orbital sander or an orbital sander for wood but it is usually acceptable for many DIY jobs. To sand rough wood smooth, start with a low grit sandpaper and work your way up gently stroking the angle grinder over the wood’s surface each time.
How Can You Use Sanding Discs?
The general method of attaching sanding disks to angle grinders is by use of a soft foam pad with Velcro backing. The pad has an attachment that screws onto the angle grinder screw and Velcro-backed sanding disks attach to the front plate. When the sanding disks are used up and you need to change them, it is just a simple task of pulling the two Velcro surfaces apart and attaching a new one.
Sanding disks are available in all grit sizes you could think of. They are meant for use during the end of a task or project for finishing off prior to polishing. However, they are not ideal for heavy use or for removal of a lot of metal.
Using sanding disks is generally the safest type of angle grinder attachment because in the case of a failure of the disk, only paper will be ejected. However, sanding disks used on steel can still produce a lot of sparks especially if a low grit is used. Safety precautions should still be followed including eye protection, a face shield and protective gloves.
Sanding disks are not recommended to tidy welds or remove slag as this may damage the disk quickly. They are designed for use on flat surfaces for polishing, removal of rust and paint and for finishing, not only for metal but also for plastics, ceramics and glass. With glass, extra care and safety precautions should be made to avoid injury.
Note that harder materials, such as steel, glass or concrete, require special sanding discs. They come with harder and more durable abrasives, e.g. of diamond tool.
An angle grinder is probably one of the most versatile handheld tools if you use it with attachments that fit for the particular purpose. If you need to remove and trim material, you will want to go for grinding wheels. Flap discs are ideal for grinding metal surfaces, and they also produce less sparks than grinding wheels. Sanding discs are available for a variety of materials and they are generally used for sanding and finishing.
Make sure you read our article on how to use a grinder before you start
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How to Change an Angle Grinder Wheel
We show you several ways of how to change an angle grinder wheel. You can do this in any number of ways—even if you’ve lost your spanner wrench. Don’t worry, all hope is not lost!
Note: Want to see a video of how to change an angle grinder wheel using these same methods? Check out our YouTube tutorial!
How to Change an Angle Grinder Wheel with a Spanner Wrench
What you need:
- Your angle grinder
- The spanner wrench that came with your angle grinder (different models use different sizes, so another may or may not work)
- A grinder wheel you want to install
Here’s how to change a grinder wheel with a spanner wrench:
- Locate the wheel lock button (usually on the top). Press it down and rotate the wheel until you feel it lock into position.
- With the button held down, place the two knobs of your spanner wrench into two opposite holes on the flange holding the wheel in place (the flange is the round nut-looking piece that holds the wheel in place.
- While pressing down the wheel lock button, turn the spanner wrench counter-clockwise until you feel the flange loosen.
- Hand thread the flange off.
- Slip your new angle grinder wheel on, and reverse the process.
How to Replace an Angle Grinder Wheel Without a Spanner Wrench
Sometimes you misplace your spanner wrench – it happens a lot unless the wrench stores on the tool the way Skil’s PWRCore 20 angle grinder does.
What you need:
Here’s how to change an angle grinder wheel without a spanner wrench:
- Hold down the wheel lock button and turn the wheel until it locks in place.
- With gloves on, grab the wheel and turn it counterclockwise until you feel the flange release.
- Hand thread the flange off.
- Swap the wheel and reverse the process.
This method works, but there are a couple of considerations. First, I’m not as confident in tightening the wheel by hand, so I always use a spanner wrench to make sure it’s tight enough.
Second, thin abrasive cutting wheels are more prone to breaking or weakening with this method, so we don’t recommend you try it with those. You could inadvertently create a situation where your cutting wheel fails with dangerous consequences.
Many Pros do another take on this by running the wheel against concrete to loosen it rather than by hand. Either way works and carries the same warnings. I personally find loosening by hand easier.
The Easiest Way to Replace a Grinder Wheel
My favorite way to replace an angle grinder wheel involves switching out the stock flange with a Hilti Kwik-Lock flange. We originally used on Hilti’s 36V grinder and find it an excellent upgrade for any model that has the same 5/8-inch arbor.
The genius of it is a design that allows you to hand thread and tighten/loosen with just your bare hand. It’s perfectly secure and super-simple.
In the event your grinder wheel helps tighten it down too much, two holes let you get a spanner wrench in to work it back off.
Here’s what you need:
- Your angle grinder
- A Hilti Kwik Lock flange
- A grinder wheel you want to install
Here’s the easiest way to change an angle grinder wheel:
- Hold the wheel lock button down and turn the wheel until it locks.
- Turn the Kwik Lock flange counterclockwise by hand until it loosens. You’ll feel some spring tension movement first before it breaks free.
- Hand thread the flange off.
- Swap the wheel and reverse the process.
The downside is that these flanges cost a little more than 50 each. That might be too steep for a DIYer. Having a couple of these on hand for Pros that use grinders often can make life easier, though.