Grinding Wheel vs Flap Disc vs Sanding Disc: What Is the Difference?

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angle grinder attachments

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) $$
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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

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.


A grinding wheel.
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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 Discs

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.


Flap discs.
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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


Sanding discs with different grits.
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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.

Conclusion

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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