Torque and thrust overload detection system for a machine tool

Abstract

A toolholder assembly is divided into a drive toolholder coupled to the drive spindle of a machine tool, and a driven toolholder carrying a cutting tool such as a drill. The driven toolholder is coupled end to end to a drive toolholder so as to be rotatable relative to the same through a preassigned angle about the toolholder axis. A coiled torsion spring acts between the drive and the driven toolholders for torque transmission from the former to the latter. The drive and the driven toolholders have interdigitating teeth with clearances therebetween. A phase detector such as a proximity switch detects a relative phase displacement that will occur between the interdigitating teeth against the force of the torsion spring upon development of abnormal torque load on the cutting tool. Preferably, the interdigitating teeth have bevels in sliding engagement with each other for causing a relative phase displacement between the teeth upon axial displacement of the driven toolholder toward the drive toolholder, so that not only abnormal torque load but also abnormal thrust load on the cutting tool is detectable by the phase detector.