Runout Wobble on the Chuck?

[Carlos]

Hi, so I just bought an South Bend 9. I did some cleaning work and believe now its perfect.

However, there is a wobble on the 3 jaw chuck. I tested it with an test indicator, see attached two pics showing how much of wobble.

I did the same test on the Lathe shaft and its pretty stable. The indicator doesent move much.
On the chuck it looks bad ...

Now is that normal or is the chuck somehow bad.... its so massive steel that I have troubles to believe its distorqued.

Please let me know what you think. Thanks.

[John Hasler]

Runout on the outside of the chuck means nothing. Put a piece of precision shaft in the chuck and measure that up close to the chuck.

[Carlos]

ok, that is a good advice. Thanks John, I try that.

[Carlos]

I tried measuring on a aluminum shaft. The wobble is even bigger. See pics.

Is there something I can adjust on the chuck? I have trouble to believe such a massive piece would wobble.

The chuck is a Union MFG Co., New Britain Conn. USA. Anybody know that brand?

[Carlos]

The test indicator I use is 0.0005''.

[NP317]

An aluminum rod is likely to not be round, since they are often extruded.
Use a (ground) steel rod like drill rod. The larger the diameter the higher the accuracy of measurement of runout.
RussN

[Harold_V]

It would be wise to run your indicator on the face of the chuck. That will disclose if the chuck is not perpendicular to the spindle. If it isn't, you must determine if the spindle is true, or not. I read that you've already tested that feature, but if it's bent ever so slightly, the runout on the face of the chuck will be far greater than the amount you determine at the spindle.

Assuming you find that the face of the chuck runs true, and that the spindle is not bent, you can safely assume that the chuck is not properly located on the backing plate, which is something that you can fix. At this point, no need to discuss that until you know where the problem is.

The advice to use a known straight and round piece is sound. However, drill rod may not fit that description. While it's ground, it is ground in long lengths by a centerless, and is prone to being out of round and may or may not be straight. If you do not have access to a known hardened and ground pin (like a drill blank or a large dowel pin), it might be a good idea to turn a piece between centers. Size and even (slight) taper isn't critical in this instance, so long as the piece is straight, and turning between centers will assure that. Do not turn by holding the piece in your chuck, as that defeats the purpose of turning between centers. Do your testing and detail what you discover so you can get sound advice on how to proceed.

Do not expect your three jaw chuck to hold within less than a couple thousandths. If it does, you are fortunate. Also, expect that it may not hold parts parallel to the spindle centerline. That's not at all uncommon for chucks that have experienced a crash, or have outlived their normal useful life. That's caused by the slides for the jaws distorting, allowing the jaws to grip only at the rear most portion (inside the chuck). You can check for that by gripping a straight piece of material then trying to fit a .0015" feeler gauge between the jaws and the gripped piece at the outside end of the jaws. If the feeler starts, or goes without effort, your chuck is sprung. That condition can also be addressed, but for right now it's important for you to determine exactly what the problem is. We'll go from there once you have reported what you discover.

H

[John Hasler]

Harold writes:
Do not turn by holding the piece in your chuck, as that defeats the purpose of turning between centers.

A part turned in a chuck with runout will still be round. For his measurement he must both grip and measure on the turned portion, of course.

[whateg0]

Harold writes:
Do not turn by holding the piece in your chuck, as that defeats the purpose of turning between centers.

A part turned in a chuck with runout will still be round. For his measurement he must both grip and measure on the turned portion, of course.

That's what I was going to suggest.

Also note that when you check runout in the spindle, you may be very close to the bearings, so runout will be pretty minimal. The farther you get from the bearing, the worse the runout will be if the spindle is bent, which is what I experienced on my old lathe.

If you have collets to fit the chuck, and the taper isn't mangled, you could gather some anecdotal evidence by putting known round and straight bar stock in a collet in the spindle taper and see how well it points to the TS.

Dave

[SteveM]

If you were to remove the chuck from the backing plate and test runout on the the face of the backing plate, runout would indicate that the backing plate is not running true and it would need to be faced.

If it is running true, then the register (the raised portion that locates the chuck) may not be concentric with the spindle.

Also, if you do as Harold says and use something like a drill blank, does it indicate the same amount out near the chuck as it does away from the chuck? If so, then the chuck is gripping straight, but off center. If the runout gets worse as you go away from the chuck, then it is gripping it crooked (and possibly off center as well).

In any case, the important thing to do is to test everything first, determine the potential causes and work out a plan of attack before machining anything.

Steve

[Carlos]

Hi all, that are all very good advises and gets me going knowing how to attach this.

I will do all and let you know the outcome.

Thanks for all the help.

[Harold_V]

Harold writes:
Do not turn by holding the piece in your chuck, as that defeats the purpose of turning between centers.

A part turned in a chuck with runout will still be round. For his measurement he must both grip and measure on the turned portion, of course.

Correct, assuming the chuck isn't sprung, at which time it's entirely possible that the turned piece will have three sides.

I should have been more specific. What I meant was to not turn a piece held in the chuck and supported by a center. That's a sure recipe for a less than straight piece, especially on light duty machines, where the tailstock is free to oscillate. That's a lesson learned at the school of hard knocks, not just theory.

Turning between centers is the way to create straight pieces, meaning pieces free of bowing. While it may end up tapered, it will be straight as the OD relates to the centerline, which is desirable when one is trying to determine where there is error. It gets too complicated to do test with less then straight shafts, generally resulting in readings that have little value, if any.

When work is done between centers, any movement due to stress relief will be self corrected, assuming roughing and finishing cuts are taken. That's why I recommended turning the required shaft, and specifically by doing so between centers. What he's looking for may be minute----so precise methodology is required in order for the real problem to be determined. Getting close serves little purpose.

H