When aligning a lathe headstock with a test bar in the spindle, it's possible to compensate for runout and error in the test bar by indicating the end of the test bar and rotating the spindle. The extremes of the indicator travel are noted and then the spindle is rotated until the indicator reads the midpoint. At this point the test bar cab be swept, the path the indicator sweeps will be fairly accurately parallel to the axis of rotation.
My question is:
How do I do the same thing on the tailstock? I want to mount a test bar in the tailstock quill taper, and sweep it with an indicator to align the tailstock. But if there is any error in the test bar, that error will be transfered to the tailstock when I scrape it. I can't use the trick mentioned above because I can't rotate the tailstock quill.
I have tried rotating the test bar 180º and taking the measurement a second time, and averaging the result. But I don't think this will be that accurate. Is there a better way?
My question is:
How do I do the same thing on the tailstock? I want to mount a test bar in the tailstock quill taper, and sweep it with an indicator to align the tailstock. But if there is any error in the test bar, that error will be transfered to the tailstock when I scrape it. I can't use the trick mentioned above because I can't rotate the tailstock quill.
I have tried rotating the test bar 180º and taking the measurement a second time, and averaging the result. But I don't think this will be that accurate. Is there a better way?