Main spindle device for machine tools

摘要

A main spindle apparatus for machine tools wherein a tool holder (T) having an anchoring edge on an inner circumferential surface and inserted into an attachment hole of a main spindle (1) is anchored to the main spindle (1) by expanding a collet (12) having an anchoring portion on the outer circumferential surface so that the anchoring portion engages with the anchoring edge. Pressure receiving surfaces (12b, 12c) which gradually decrease in diameter in approaching the tip are formed on the inner circumferential surface of the collet (12). The main spindle (1) is provided with a push rod (2) which expands the collet by means of pressure applying surfaces (2d, 2e) formed on the outer circumferential surface and gradually decreasing in diameter in approaching the tip, which press the pressure receiving surfaces (12b, 12c) of the collet (12) when the push rod (2) is moved forward so as to approach the tool holder (T).