Originally Posted by
cba_melbourne
- The two collar method bases on the assumption that the headstok has been accurately scraped to the bed. To verify this assumption, a test bar is needed.
- Colchesters are expensive lathes and it is safe to assume headstock to bed are accuratly scraped together and can repeatably be reassembled. But low cost lathes do rarely have the headstock scraped to the bed (else they could not be low cost). On these machines headstock alignment is done by torque shimming. Which is not repeatable neither in the horizontal nor in the vertical plane. Hence the need for a test bar. The two collar method cannot work in this instance, because the spindle center line can be tilted up and down quite a lot, before you would notice a diffence in two collar diameters. The two collar method is very sensitive in the horizontal plane, but not so in the vertical plane.