Truing (?) 3 Jaw Chuck

mikeyjones · Apr 23, 2022

Hey guys -

I have a 3 jaw Buck Chuck that came with my LeBlond lathe. Noticing an issue with it that hopefully someone here has insight on how to fix.

Only 1 out of the 3 scrolls gets it close to true. To explain: using scroll A the chuck has < .001" runout at the jaws (as measured by a precision ground rod). Using scroll B or C, it's .01 - .015". I can repeat this all day by tightening the bar using scroll A, measuring runout, then loosening/tightening using one of the other 2 scrolls and measuring, then going back to A and repeating. Without rotating the bar or doing anything else - just by using scroll A, it goes back to .001" runout.

So what would the best way to get the other 2 scrolls back in line?

I've disassembled, cleaned and greased the insides already to no avail.

Any help is appreciated.

TGTool · Apr 23, 2022

I think you mean different pinions, A,B,C. There's only one scroll. It's the nature of three jaw chucks to develop that characteristic as a result of wear. The answer is to use the A pinion if you want the best accuracy on your stock.

Some chucks are marked with a "0" to show which to use for best accuracy.

guythatbrews · Apr 24, 2022

With this much difference between pinions I'd be concerned about damage. Maybe distorted by a big wreck. Have you checked to see if the outside of the chuck is round?

When you took it apart did you inspect the fit of the scroll in the chuck? They are usually tough to remove because of the close fit.

I think the only thing that can cause your problem in a universal chuck is the scroll moving side to side in the chuck body depending on which pinion you tighten. The scroll needs to be a very good fit in the chuck. Maybe it was abused prior to your ownership. Maybe running the same size stock a lot with junk grinding out a spot in the body of the chuck allowing the slop.

Let us know I'm curious whay this is happening.

moonlight machine · Apr 24, 2022

mikeyjones said:
Hey guys -

I have a 3 jaw Buck Chuck that came with my LeBlond lathe. Noticing an issue with it that hopefully someone here has insight on how to fix.

Only 1 out of the 3 scrolls gets it close to true. To explain: using scroll A the chuck has < .001" runout at the jaws (as measured by a precision ground rod). Using scroll B or C, it's .01 - .015". I can repeat this all day by tightening the bar using scroll A, measuring runout, then loosening/tightening using one of the other 2 scrolls and measuring, then going back to A and repeating. Without rotating the bar or doing anything else - just by using scroll A, it goes back to .001" runout.

So what would the best way to get the other 2 scrolls back in line?

I've disassembled, cleaned and greased the insides already to no avail.

Any help is appreciated.

.001 run out? Treat it like a sore dick, don't f*ck with it!!!!! That is the most accurate 3 jaw chuck in the world. The reason it is different is the pinion forces the scroll away from the pinion as you tighten it, just the luck of the draw that it centers to .001

mikeyjones · Apr 24, 2022

guythatbrews said:
With this much difference between pinions I'd be concerned about damage. Maybe distorted by a big wreck. Have you checked to see if the outside of the chuck is round?

When you took it apart did you inspect the fit of the scroll in the chuck? They are usually tough to remove because of the close fit.

I think the only thing that can cause your problem in a universal chuck is the scroll moving side to side in the chuck body depending on which pinion you tighten. The scroll needs to be a very good fit in the chuck. Maybe it was abused prior to your ownership. Maybe running the same size stock a lot with junk grinding out a spot in the body of the chuck allowing the slop.

Let us know I'm curious whay this is happening.

Outside is definitely round and when I disassembled the scroll was a tight fit, had to knockout w/ a brass rod.

I guess as someone else said, I'm just going to use the 1 pinion and not mess with it further. Just was curious if there was a way to clean up the other pinions.

mikeyjones · Apr 24, 2022

HappyWyo said:
I may be stating the obvious here, but when you tighten your chuck onto your spindle are you watching your dial indicator on the end of your rod as you rotate the spindle to make sure the chuck is being tightened onto the spindle square.
If the chuck isn't being tightened on square, one side of the chuck will appear more straight than the other side when running a dial indicator down the length of the rod.
If I can't get my 3 jaw within .001 I take it off and work on whatever the problem is causing the inaccuracy.
Most of the work we do has to be better than that.
We usually try to get out finished product within .0002 so the customer has no fit or vibration problems.

Not running the indicator down the rod, but rather rotating the chuck and watching the indicator. So if I use 1 pinion and rotate the chuck, it's less than 1 thou runout, using the other 2 it's more than 10 thou.

But FWIW, I have a L0 spindle so it would have to fit the taper to go on.

JST · Apr 24, 2022

I have used shim stock to get the scroll to be a better fit on it's bearing in the chuck. That did make the chuck more consistently repeatable overall.

mikeyjones · Apr 25, 2022

JST said:
I have used shim stock to get the scroll to be a better fit on it's bearing in the chuck. That did make the chuck more consistently repeatable overall.

So shim stock against the back of it to ensure it doesn't wobble front to back?

JST · May 1, 2022

mikeyjones said:
So shim stock against the back of it to ensure it doesn't wobble front to back?

No, shim stock around the central pivot to take up the slop space so the scroll would not shift around. Basically a make-do, but it worked and I still use the chuck on occasion

eKretz · May 2, 2022

I am in the process of a rebuild on a Buck 6-jaw. I'm planning to turn the inner pilot down enough for a 4140 Q&T sleeve, then cut the inside diameter of the scroll plate for a close fit again. May trim both faces of the scroll and any necessary inside surface of the chuck and add some hard shim to take up the gap. Can't cut the chuck in certain places without recutting the pinion bore and possibly affecting the lash, which I'd rather avoid.

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