What Are Abrasives?
Abrasives have this mineral material on them to create friction to either reshape a surface/workpiece or to give the surface a finish -- whether that is a smooth or polished finish. Depending on the specific product you buy, you can accomplish different outcomes like buffing, lapping, grinding, cutting, polishing, etc.
Abrasives can remove unwanted material from a workpiece and depending on the grit size you use, you can remove the amount of material you want faster and easier. The abrasive grits remove material because they have harsh edges and while being used with a tool, can remove stock better. Harder or more coarse grits can remove stock faster. The smaller the grit size, the finish will be finer. If you have a heavier hand with more force, you will achieve a faster abrasion. Some tips that could come in handy for you is to make sure you're not using an abrasive product when it is worn down or has reached the end of its life because it will not cut your workpiece efficiently. Also, a cooling system and a vacuum system can help a lot as well to keep unwanted dust from flying everywhere and to avoid overheating and burning.
Different Abrasive Products
Abrasive products include sanding discs, sanding belts, sanding sheets , or sanding rolls -- these are most commonly used and one can be better for you than the other depending on the job you are doing. Sanding discs are great for prepping your surface, removing rust from metal , or giving a finish to wood. They are also best for larger surfaces. Sanding belts are good to remove stock faster. For example, knife makers would consider using this, along with sharpening tools, removing paint layers, and hardwood floors. Sanding sheets are usually used when you do not need to remove a lot of stock, considering it is more of a hands on labor. However, these could be good for getting into tight corners and edges. Lastly, sanding rolls can be good for giving a nice finish to a surface -- mainly wood, but can also be used on metal or plastics.
Silicon Carbide - highly friable, moderately strong, moderately expensive, moderate lifespan.
Aluminum Oxide - Highly friable, weakest material, cheapest option, least long lifespan.
Zirconia - Moderately friable, moderately strong, moderately expensive, moderate lifespan.
Ceramic - Least friable, strongest material, good price, most long lifespan.
Silicon Carbide gives a nice even cut so most people like to use them for finishing a workpiece. The cutting rate stays the same throughout the belt lifespan. These belts are more expensive than aluminum oxide because they are harder and sharper with good consistency. These are usually black in color and are good to avoid overheating.
Aluminum Oxide is actually the most common or popular material. There is an open coat aluminum oxide or a closed coat aluminum oxide. The open coat is only semi covered in the back (50-70 percent) and they are good for stripping and finishing all types of wood. Closed coat aluminum oxide have grains that are stuck together evenly without openings and are good for removal and grinding for metals.
Ceramic is a very sharp material and are great for cutting metals and wood. When using ceramic belts, high pressure and high speed is ideal, however, be careful of burning the surface.
Zirconia is also a harsh/sharp material and can be used for grinding and polishing metals or wood like ceramic.
There are different abrasive backings like the paper backing, cloth , plastic, or foam and sponge. Paper backing is lighter and usually cheaper compared to cloth backing. They achieve even cuts and can sometimes be more flexible/durable. These come in weights A-F. A and B weights are common in finer grits and hand sanding. C and D weights are for general sanding while the E and F weight are mostly used for belts or discs. Cloth backings can be polyester (which is waterproof and has good strength), cotton, or poly/cotton. Cloth backings are popular due to their strength and lifespan. These also come in weights J, X ,Y and YY. J weight is the most common and flexible while also being really light which is good for metal finishing. Plastic film backings are also waterproof, so they are good for wet sanding. They also give a precise finish. Foam and sponge backings are good for hand sanding and can be very flexible to get the contoured sharper areas.
There are a variety of grit sizes and the lower the size, the more harsh and coarse the grit is. For example, a P36 grit is very coarse and should only be used if you have to remove a lot of stock at once.
The very coarse ones are P8 through P80. These are good for stock removal and getting rid of paint layers. The medium ones are P100 through P220 -- which can sharpen, shape, prep, or remove planning marks. Any grit size that is P240 or higher is going to be very fine. These are used for polishing surfaces and sharpening.
Overall, choosing the best material and grit size for the job you are working on will help you tremendously. For knife making, we recommend closed coat aluminum oxide, ceramic, or zirconia. For wood, aluminum oxide is best -- softer woods use an open coat and harder woods use closed coat. For metals, ceramic and closed coat aluminum oxide is best, but zirconia can be good too.