Maximum Force Restriction:

In operations where workpiece dimensional accuracy is important cutting force 'Fc' should not be too high otherwise tool may vibrate and may lead to form error. As a result, the dimensional accuracy may not be achieved as desired.

The cutting force may be expressed as :

F_c  = E f ^α d ^β   

Eq. gives a maximum allowable feed for the given depth of cut. For this restriction, the feed chosen is such that it gives the maximum force (within permissible limits, i.e. Fc ≤ Fmax).