Grinding Wheels and Abrasives

A grinding wheel cuts with many small grains

A bonded wheel holds abrasive grains in a supporting material called the bond. The grains act as small cutting edges. Spaces between them provide room for removed material and, in wet grinding, fluid. Grains can fracture or pull free as the wheel works; dressing restores a useful cutting surface when that renewal is insufficient.

Choose the complete wheel for the machine, material and operation. Abrasive type alone does not establish suitability: shape, dimensions, bond, speed rating and permitted grinding surfaces also matter. See Offhand Grinding and Precision Grinding.

Match the abrasive to the work material

Abrasive	General starting applications
Aluminum oxide	Steels, including high-speed steel (HSS) tool bits. Different formulations serve different grinding conditions.
Silicon carbide	Cast iron, some nonferrous materials, and brittle nonmetals; also conventional carbide-tool grinding with a suitable wheel.
Cubic boron nitride (CBN)	A superabrasive used for hardened steels and HSS.
Diamond	A superabrasive used for cemented carbide, ceramics and other hard nonferrous materials. It is not the general choice for steel grinding.

These are selection starting points, not permission to use any wheel containing that abrasive. In particular, a standard bench wheel for steel is not a wheel for aluminum. Confirm the manufacturer's application listing.

Manufacturer resources for abrasive selection

Norton: choosing a grinding wheel discusses conventional abrasives. 3M: CBN and diamond superabrasives covers the superabrasive families. Use product-specific data for a real selection.

Grit is grain size; grade is how firmly grains are held

Grit size: within the same conventional grit-number system, a lower number means coarser grains and a higher number means finer grains. Coarse grit generally provides more space for chips and favors material removal; fine grit generally favors smaller scratches. Finish also depends on dressing, feeds, wheel condition and the work material.

Grade: the wheel's resistance to releasing abrasive grains. A hard grade holds grains more strongly; it does not mean that the abrasive mineral itself is harder. A hard work material may need a softer grade so dull grains can release.

Structure: the spacing of the grains. An open structure provides more space between grains than a dense structure. Do not confuse spacing with grain size.

Bond: vitrified bonds are glasslike; resinoid bonds use resin. Rubber and metal bonds serve other applications. Bond choice affects wheel behavior, dressing and permissible operating conditions; no bond name establishes a universal RPM rating.

Read the conventional marking from abrasive to bond

The usual core sequence is abrasive → grit → grade → structure → bond. Prefixes and suffixes may identify a manufacturer's particular abrasive or bond. Some markings omit a structure field. Superabrasive specifications may include concentration and use a different format.

For a teaching example, suppose a supplier defines A 60 J 7 V as aluminum oxide, grit 60, grade J, structure 7 and vitrified bond. The 60 is not an RPM limit; the J is not the hardness of aluminum oxide. Use that supplier's key to interpret J and 7 rather than assuming all manufacturers' grades behave alike.

A manufacturer's explanation of the marking

Norton: Grinding Wheel Basics explains the five fields and manufacturer-specific variations. A wheel specification and its separately marked maximum operating speed answer different questions.

Practice decoding a wheel Practice grit selection