First, disassemble the chuck, clean and lubricate it. Reassemble it making sure the chuck jaws go in the correct slots, and started at the correct times. Then try it again.? A really good ?quality?3-jaw self-centering chuck will still have .003" of run-out. There are a number of schemes to let them be adjusted to better run-out, and both Buck and Cushing use them on some of their more expensive chucks. You may have one of those that has been opened up, and not reset. Or the thing can be incredibly dirty inside. Saw a video yesterday that showed a guy testing a standard non-adjustable Craftsman chuck. Which was over .020" out. He ground the jaws, then disassembled it to clean it out. Cleaned and reassembled, it was right at .003" run-out.? Here it is:?

I'd do the cleaning and such first! I have an atlas chuck of my own that's .014" out. Haven't been able to get mine apart, yet.?

Bill in OKC

William R. Meyers, MSgt, USAF(Ret.)

Aphorisms to live by:

Good judgement comes from experience. Experience comes from bad judgement.?

SEMPER GUMBY!

Improvise, Adapt, and Overcome.
Physics doesn't care about your schedule.
The only reason I know anything is because I've done it wrong enough times to START to know better.

Expect in one hand, expectorate in the other. See which one gets full first.

On Wednesday, December 18, 2024 at 04:27:42 PM CST, Guy Edkins <gedkins@...> wrote:

?Hi all,

I am in the process of rehabbing a 3995 lathe. It was free and maybe I now know why. The runout on the spindle inner and outer diameter is really good. Like .0013. Screw on the chuck and chuck up a mandrel and it all goes bad, really bad. You can see it, let alone measure it. The chuck is a Cushing 3 jaw.

So is it worth buying a new chuck, i.e. will it mitigate much of the issue, or is there something else at play here (see what I did there) that I have missed? I am new at lathe details and the ins and outs, but an engineer by background.


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