POSITIONING DEVICE FOR CRANKSHAFT IN MACHINING MACHINE

PROBLEM TO BE SOLVED: To position a crankshaft for a spindle of a machining machine without moving it longitudinally, by projecting a reference pin from a reference surface during processing of a positioning arm and embedding the reference pin into the reference surface during the backing of it. SOLUTION: A positioning piston 20 is proceeded and controlled to proceed a positioning arm 21, its first reference pin 23f is inserted into a reference pin hole 27, a second reference pin 23s is engaged with one of a plurality of screw holes 28, and then a crankshaft Sc is positioned for a spindle 6. Next, a chuck 4 is operated to mount the crankshaft Sc to a main shaft 2. When grinding machining of all crank pins Cp of the crankshaft Sc is completed, rotation of the main shaft 2 is stopped, the positioning piston 20 is backed, the positioning arm 21 is entered inwardly from the reference surface 17f of a reference seat 17 so that the first and second reference pins 23f, 23s are respectively drawn from the reference pin hole 27 and the screw holes 28.