L - This indicates the grade or hardness of the grinding wheel and is a
measure of the strength of the bond material. The letters range from A for soft
to Z for hard.
5 - This indicates the type of structure or the relative spacing of the grains in
the wheel; the larger the number, the more open the spacing. Its use is
optional. The omission of this number indicates that the wheel was not made
of only one structure.
V - This indicates the bond type used for the wheel abrasive.
23 - This is the manufacturer's private marking. It is used to identify variations
of a grinding-wheel composition. Its use is optional.
Two types of abrasives are normally used for grinding wheels, aluminum oxide and
silicon carbide. Aluminum oxide is softer than silicon carbide and is suitable for most
applications. Silicon carbide is used for cast iron, bronze, and for very hard materials.
Never use silicon carbide on stainless steel. Aluminum oxide should be used for
grinding stainless steel and cast steel.
The type of bond to be used depends on the final surface finish required, the amount
of material to be removed, and the type of grinding wheel. Resinoid-bond wheels are
best suited for the removal of small amounts of material and for obtaining very fine
finishes. However, the vitrified-bond wheels are the most common type and are used
for most general grinding.
The grade, or hardness, of a grinding wheel depends on the strength of the bond. The
stronger the bond, the harder the wheel. The grade needed depends on the material -
normally, hard wheels are used for soft work materials, and soft wheels are used for
hard work materials.
The grain size selection depends on the finish required and the rate of material
removal desired. A coarse grain size provides a fast rate of material removal but a
rough finish. If a fine finish is required, a finer grain should be used. Usually a fine-
grained wheel has a dense structure, and a coarse-grained wheel has an open
The grinding-wheel speed is important for the safety of the operator. Wheel speeds
vary from 4,500 to 16,000 surface ft/min (1,371 to 4,877 surface meters/min),
depending on the strength of the bond used. Most surface grinding is done in the
speed range from 5,500 to 6,500 surface ft/min (1,676 to 1,981 surface meters/min).
Never use a grinding wheel at a speed higher than that recommended by the