Making a 3 jaw adjustable.

[challenger]

I have a 6" 3-jaw with a L00 mount. It's got significant run out. I tried regrinding it without decent improvement. Is modifying this chuck to be adjustable worth the effort?
I only use a 4-jaw but the 3-jaw would be nice to have if I can get only a couple of 3 thou run out.
Thanks

 

[john.k]

Check out the insides ...you may be able to take up some of the wear ,like the fit of the scroll to the body .

 

[Billtodd]

Given that you are starting with a worn chuck, you have little to lose.
I would first machine a thou or two off the register (off of the chuck , don't ruin a probably ok backplate).
Remount the chuck and bump it concentric at a typically used diameter
Then check for repeatability at the same and other diameters
Only then would I add adjustment screw's etc

 

[Doozer]

IF a 3 jaw has a lot of wear, especially in the scroll bearing
one tip you can use is to true it up by hammering on the
outside of the offending jaw. If the high spot is on the one
jaw, hammer whack that jaw to shift the scroll (and all the
jaws) in the body. This method works better, the more
the chuck is worn. It is a work around, but very effective.
Maybe I am not describing it well, but those who know the
technique, please chime in.

-Doozer

 

[Billtodd]

One more thing.. related to Doozer 's comment above.
If the chuck has been religiously tightened using the '0' itl have worn there worst.

Try tightening with one of the other keys, you might be able to just remark the 0 and live with it.

 

[bob]

For a couple hundred dollars you can buy a Chinese chuck that will be ten times better then you will accomplish. I am as cheap as the next guy but trying to fix worn out 3 jaw chucks is a waste of time.
Bob

 

[john.k]

A Charles Taylor chuck is what you need.

 

[Doozer]

A Charles Taylor chuck is what you need.

I wish we had them in the USA.

-D

 

[john.k]

Ive bought machines with Taylor chucks just to get the chucks..............the ultimate in one upmanship............Yes,you have a $700,000 Haas ,but do you have any Taylor chucks?

 

[Peter from Holland]

On a OD grinder once I found the scroll to be turned off the ID and OD a bit
And then 4 setscrews in the body for adjusting the scroll
Simplest adjustable chuck I ever saw
Not the best The simplest

Peter

 

[Doozer]

On a OD grinder once I found the scroll to be turned off the ID and OD a bit
And then 4 setscrews in the body for adjusting the scroll
Simplest adjustable chuck I ever saw
Not the best The simplest

Peter

VERY CLEVER ! ! !
I like it.

-Doozer

 

[Doozer]

To my knowledge, a Taylor design is immune to jaw splay/bell mouthing
but the scroll bushing area can still wear and cause runout.
Is this right? Even so, the conical scroll to capture the jaws is a
genius design.

-D

 

[morsetaper2]

I had a dividing head that had a chuck & backplate w/ about .005 runout. And I modified it to be an "Adjust-tru" sort of chuck-backplate.

Details are several posts in, in this old thread from 2005 about making chucks "Adjust-Tru". My photo links are dead, might be able to find the old photos in my archive. See this old thread:

Shop Built "Adjust True"

Had a real good K&T DH and a good chuck, so added studs to chuck and made oversize adapter that would allow set screws to push on sides of studs and adjust chucked piece dead nuts. Photo below shows me putting flats on side of studs so set screws have a seat. Photo below shows parts. Maybe...

www.practicalmachinist.com

EDIT: Found my old images!

 

[MrWhoopee]

IF a 3 jaw has a lot of wear, especially in the scroll bearing
one tip you can use is to true it up by hammering on the
outside of the offending jaw. If the high spot is on the one
jaw, hammer whack that jaw to shift the scroll (and all the
jaws) in the body. This method works better, the more
the chuck is worn. It is a work around, but very effective.
Maybe I am not describing it well, but those who know the
technique, please chime in.

-Doozer

Not sure if you're talking about using this method routinely to dial a part in or as a one-time method for correcting a chuck.

As a routine method, chuck the part lightly, indicate, tap the high jaw with a soft hammer, snug a little tighter, indicate, tap the high jaw, repeat until tight and running true. This was standard procedure where I worked instead of removing a 12" 3-jaw and mounting a 4-jaw. Our chucks weren't badly worn, just typical.

 

[dutchgray]

For a couple hundred dollars you can buy a Chinese chuck that will be ten times better then you will accomplish. I am as cheap as the next guy but trying to fix worn out 3 jaw chucks is a waste of time.
Bob

I have bought brand new TOS and Bison 3 jaw chucks in 6" to 8" for that sort of money, set up a search on Ebay and jump on the first new one you see cheap, will probably be a NOS deal that's been sitting in stock somewhere for years or from a bankrupt or clearance type seller.
Might end up spending more on the L00 backplate to be honest.

 

[dalmatiangirl61]

I don't know about L00 chucks, but on my L1 chucks, the hole for the pinions is half on the backplate, half on the chuck. Skimming back of chuck would change interference of the pinions to the ring gear, and require remachining the pinion hole, if you skimmed the back plate you'd have to remachine that half of pinion hole too.

Challenger
Have you tried rotating chuck on the backplate to different bolt positions to see if that improves anything? Is your chuck completely separate from the back plate, or does the split line run thru the pinion holes?

 

[challenger]

I don't know about L00 chucks, but on my L1 chucks, the hole for the pinions is half on the backplate, half on the chuck. Skimming back of chuck would change interference of the pinions to the ring gear, and require remachining the pinion hole, if you skimmed the back plate you'd have to remachine that half of pinion hole too.

Challenger
Have you tried rotating chuck on the backplate to different bolt positions to see if that improves anything? Is your chuck completely separate from the back plate, or does the split line run thru the pinion holes?

Yes. I've tried everything over the years as the motivation comes and goes with this chuck.
I know I should just buy a new one but the 4 jaw has become so easy to use and is so easy to get a zero TIR.

 

[???]

I was given a Pacific lathe in perfect condition by a fellow shooter who retired at 103 years of age. When I picked up the lathe he told me that the chuck was not tightened 100% so that he could tap it to run true. I've left it like that and even when I hoe into 4140 it normally doesn't move and if it does all it takes is a couple of taps with a copper to get it within .01 mm or better TIR for the final cut.

Regarding refurbishing and adapting old chucks that run out a lot. Probably a waste of time as the wear will be uneven in different areas of the scroll and you will get it running true in one area and then be out in another.