The grade of
a grinding wheel is a measure of the strength of the bonding holding the individual
grains in the wheel - the major factor being the average diameter of the individual
bond A to Z in the order of increasing bond content.
If the bond post is not strong enough to withstand the forces imposed on it, fracture occurs and grain is discharged from the wheel. The wheel is then said to be "soft acting".
If this does not take place at a too-rapid rate, it becomes an ideal condition for rough grinding. However, precise control of this breakdown is quite difficult and rarely is accomplished in industry. A greater degree of control may be had for roughing by using a wheel having a somewhat larger-diameter bond post (higher in the alphabet grade letter) and free running mechanical roll dresser such as a Desmond.