Acceptable run out for old 3 jaw chuck?

D

dontrinko

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I bought an old craftsman 3" 3 jaw chuck. The run-out was .012" After "fiddling " with the jaws by hand grinding I have it down to .006" I do not do anything precision. Is this acceptable for an old chuck?

I do not have the necessary stuff to grind in the chuck. Thanks; Don
 
Take the chuck apart, clean it up, and inspect it. Just cleaning it up often improves the performance. Look closely at the scroll groove for crud and for wear and damage from over tightening. The chuck might be more or less accurate at other diameters due to the design of the chuck and the scroll. It is not really a good idea to hand grind on the jaws, without first determining what the problem(s) are. "A single good test is worth a million expert opinions." Reassemble using oil, not grease.
 
It's not hugely important if you are doing a complete part in a single chucking. It only becomes an issue if you need to machine something on a part that is already been made, or need to flip a part around and do the other side or end. And even then, in most cases, some lack of concentricity can be acceptable. Only you can make that determination. As much as we all would like to make zero runout parts, that isn't going to happen in two or more chuckings. When runout is critical, that's when to turn to a 4 jaw chuck or a collet system.
 
I would think if a 3 jaw would give between 0.003 and 0.006" runout, then that would be good. Also would want to mount, check, take off, remount and check again to make sure the registers are ok.

As has been mentioned, I use a 4 jaw independent is the way to go if you want something closer.

David
 
If you have a dremel tool or die grinder you have the means to grind that chuck.
 
i made this (crappy) video a few moons ago..
dremel held in a lantern toolpost holder



i was able to see .003" on .500" dowel pins upon completion
 
I used 2 hose clamps to attach an air die grinder to my QCTP to grind mine.
 
I guess it's worth mentioning, if you take the chuck apart, be sure to mark the location of the jaws, so you can easily reassemble in the correct order. I think the jaws only go back in one way, but marking them 1), 2), 3), will save you several moments aggravation when time to reassemble.
 
Thanks everyone. I do have a 4 jaw and I use it most of the time. Not that hard to adjust once you get the hang of it.
I'll use the 3 jaw when I am making something simple that does not require changing in and out of chuck. Don
 
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