Runout Wobble on the Chuck?

[pete]

Given the picture in Carlos's first post I'd say more than one test is going to be required before the exact issues of what's causing the problem can be nailed down. I'd first remove the chuck and check the spindle mounting threads for burrs, then indicate the locating flanges face and O.D. of the spindle. For good measure I'd also indicate the spindles Morse taper just as a double check while I was at it. Once those numbers are known then that area can either be eliminated or judged as at least one part of the problem. Then I'd spotlessly clean the spindle nose, it's threads, the chuck back plate threads and it's locating recess. Install the chuck and then hold whatever you have available that was known to be quite round. The ground shank of a 1/2" twist drill as one example. But every shop is going to have something in it some where that's safe to assume that it is round. For that drill, Hold it by as much of it's plain shank as possible and indicate that plain un-fluted portion just before the drill flutes start and up tight to the chuck jaws. Then I'd pull the chuck jaws and check the run out on the face of the chuck. Those tests should give you some base line numbers for the spindle and chuck. This doesn't properly test the chuck for the exact problem since the back plate could have been machined incorrectly, it could be sprung, or the jaws seriously worn. It might even need a really good internal cleaning. But if that spindle nose checks out it can be eliminated and the issues are else where. Then it's time to measure the back plates recess, possibly separate it from the chuck and reinstall it back on spindle and check it's concentricty while it's in it's running position. You have to do a series of separate tests for each area on the machine and have some repeatable test numbers that are known to be 100% dependable before you can start to pinpoint what is or isn't part of the problem. Head and tail stock alignments are well outside the original issue and other tests are required to deal with any other possible problems those areas of the lathe might have. Run all those tests then come back with some hard numbers Carlos and then some better educated guesses might be made of where your problems might be coming from.

[John Hasler]

pete writes:
> Given the picture in Carlos's first post I'd say more than one test is going to be required
> before the exact issues of what's causing the problem can be nailed down.

All we know now is that he sees runout on the outside of the chuck and on a random piece of bar stock. Seems to me the first thing to do is to find out if he has any problem at all. Measuring runout on a drill bit as you suggest seems like a good first step.

[pete]

Yep good point, there could be multiple causes and fixes from it's already just fine, to dead simple and free on up to possibly complex or expensive. Carlos's pictures show what I think is an old chuck so it's untested and unknown what it's condition is right now. Buying used home shop equipment always comes with a certain amount of risk for what your really getting and how it was looked after and used by the previous owner. So you can't blindly trust anything and have to verify what you've got first.

[Harold_V]

A caveat in regards to using drill shanks for anything precision.
It's common knowledge that the shank of a twist drill isn't hardened, plus it is usually imprinted by impression stamping, although that is now being replaced by other marking methods.

Back to the issue at hand, if the twist drill used hasn't been gripped in a chuck, it may serve adequately, but if it has, it most likely is no longer round, as the chuck will have deformed the shank, albeit in a modest way. One is better served, by far, to select a drill blank for test such as this. If a drill blank isn't at one's disposal, perhaps a dowel pin might be. Both of them are precision ground and held to exacting sizes, and are typically dead straight.

H