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.

Abstract: An indexing apparatus for a rotary table has a support shaft rotatably supported by a base member in which indexed terminal positions of the rotary table is determined by abutment of a stopper member provided on the rotary table against positioning members provided on the base member. The indexing apparatus comprises a rack-pinion mechanism comprising a rack and a pinion fixed around the support shaft of the rotary table for rotating the same, a feed screw shaft rotatably supported by the base member and extending along the rack in a direction of the movement thereof, a breakable electric motor for driving the feed screw shaft, and a feed nut engaging the feed screw shaft. The rack and the feed nut are arranged so that either one of them has integral portions disposed at both sides of the other with spaces left on both the sides in the direction of the movement of the rack. Annular springs are disposed in each space.