Predictive Force Models for Point-Thinned and Circular Centre Edge Twist Drill Designs

Abstract

The geometry and specification of point thinned general purpose and facet point drills as well as the patented ‘circular centre edge’ twist drill design are studied and used to develop predictive mechanics of cutting models for the thrusts and torques for these drill designs. It is shown that the three designs involve point thinning, to improve the rake angle and cutting action at the chisel edge, with the circular centre edge drill being a variation of the point thinned facet point drill. The predictive models have been numerically and experimentally tested. While these drill designs substantially reduce the thrust force when compared to unthinned drills the difference in the forces for the three designs are minimal when compared on a fair basis. The importance of geometry and force modelling in assessing drill designs is highlighted in this work.