- Dec 15, 2013
Hello and best wishes to all watch enthusiasts! I need some help on figuring out what is wrong with my lathe and what can be done to improve things. I've bough vintage American lathe some time ago, classic ww type, and later added faceplate, 3-jaw chucks, cross slide and other things, but never was satisfied with how it worked. As all parts were from different sources it was difficult to find which part contributed the most to bad accuracy. But this time I decided to try. My task is to turn flat rings from copper and silver, from a square sheet blank about 1 mm thick. I made a thicker brass plate to make the workpiece more solid so it doesn't bend when turning and attached both to the faceplate. The problem is I can't turn the metal evenly, it is always that one side of the circle left by the graver in the cross slide digs in considerably while the other side isn't even scratched (see my test copper plate in screenshot). It looks like the faceplate doesn't remain in one plane while rotating as if it had a bent arbor. I measured all three dogs and they are 10.90 mm of height each (could be off about 0.02 mm depending on placing the caliper). Then I tried to measure how much out-of-plane variation I have by putting a graver at the out-most part of the faceplate and rotating by hand. It scratched the most in one place. I marked this place and loosened and rotated the faceplate, so it occupied a different position relating to the headstock bearings (this is possible because the slot pin is broken). This time it scratched the most in a different place. And I found that the scratchy spot changing with each changing of faceplate position relating to the bearings. The scratching is quite subtle though, looking with a naked eye it's hard to notice that the faceplate rotates out of plane. I also made the same experiment with a smaller disk chuck and also by putting some metal rod to the surface of the cone inside the headstock. In all cases it scratched the most in some spot, not evenly around (should it be so?). The headstock itself doesn't show any play in the bearings that I can feel when trying to move the faceplate in different directions, and turns quite freely, though no effortlessly. I didn't take it apart yet. Excuse me for this long message, but has anybody come across a similar case and what is the best way to rectify the problem? I find it difficult to turn flat rings with this setup as the variation across the cutting circle is too big, negative rake graver digs in if I try anything but the most gentle feed and pulls the work out of place if I turn faster. I tried this quite a number of times and filed the edges of my sheet blanks so I don't think it's because they are bent or have burrs. Any thoughts and suggestions are very welcome!