Fun times with runout! This is on an old 3-jaw chuck on a southbend lathe.
Ideally, that needle would be completely still, but there’s crazy run-out. Run-out is a type of mechanical ‘out-of-whack-ness’ that is usually used to describe how much a rotating thing spins and whips around like a cookie dough mixer versus a perfectly straight rotating shaft. In this case, I put an edge finder in the lathe chuck, which by all accounts ought to be the straightest and most perfectly ground thing in the shop. To that, a dial test indicator is placed, and the lathe or whatever you happen to be testing, is turned on to SLOW. The amount of wiggle on the dial is read, in this case, it’s about 0.015″ which is a LOT for something that would ideally have less than 0.001″ of wiggle.
At this point, you take the chuck off, take the jaws out and clean the living crap out of everything, look for burrs and dings on the jaws, clean, re-assemble, and re-test and hope everything gets better. Barring that, you would need to do a whole new operation involving a tool post grinder and a whole bunch of other crap to re-grind the jaws of the chuck so that they’re properly centered.
Now, don’t get me wrong, you can still make nice parts on this lathe, but you have to start with a new part that you remove at least as much material from as you have out-of-whack-ness (runout) and then, after that, you can’t remove the part from the chuck until you’re completely finished. Kind of makes doing operations on existing parts or doing backside operations impossible.
For those, we end up using the 4 jaw chuck and manually dialing it in, which is very time consuming, but really the only way we can achieve good results.
Maybe some day we’ll fix it.
1 year ago