Insert grade/geometry?
Is the chuck greased regularly? Could it be exerting less radial force for the same hydraulic pressure due to lack of maintenance?
Are you running off the bar, or would it be possible to use stepped soft jaws?
EDIT: just saw the note about turn to drive ratio. use accurately bored stepped soft jaws and get a shoulder/face positively located.
EDIT2: but check to see that you're getting good grip first. This job shouldn't be slipping assuming a reasonable DOC. (0.1ish on a middle weight lathe - what kind of machine?) |