3 jaw chuck runout?

S

skeetlee

Active member
The new import 3 jaw on my lathe has a little bit more runout than i would like. My question is. If i can find a tool post grinder can i touch up the jaws a bit or will i just be chasing my tail. I do have a better 3 jaw chuck " plain back" that i was going to use on my turn table for the new mill, but maybe i should bite the bullet and buy the proper d1-6 back plate and just go with that one? The dam back plate for this chuck is around 3 bills. I almost hate to buy one, as im not garanteed the Bison chuck will be any better. On my import that came with my machine i have .006 total runout on my dial indicator, so thats .003 off center. I know this is with in standards, but i would like to have one a little better that this. Lee
 
Even if you true the jaws with the tool post grinder at a particular diameter, how do you know it will still be true when you scroll to a different diameter? My humble opinion is that you don't. Your mileage may vary.

Regards,
Ron
 
RJM said:
Even if you true the jaws with the tool post grinder at a particular diameter, how do you know it will still be true when you scroll to a different diameter? My humble opinion is that you don't. Your mileage may vary.

Regards,
Ron
Click to expand...
Ron is correct. Unless your chuck has a perfectly machined scroll, all the other jaw positions may produce runout as well.

Don't expect too much from cheap quality chucks. Also, very important, many of these cheap import chucks are dangerous to operate above about 600 rpm!!
 
Lee buy yourself a good "Strong" brand 3 jaw chuck.........mine has less than 0.001" runout.

When I got it I put a piece of 1" tool steel in the jaws and mounted the chuck on the spindle in the six different positions.......one position had less runout than the others, I also tightened the jaws on the tool steel using each different chuck key position and found one position repeatedly produced less runout than the other two, the result is less than 0.001" runout repeatable at different diameters.

I'm quite happy with my 3 jaw chuck..........Ian
 
I have an old steel Buck adj.tru 3 jaw i wouldn't trade or sell for anything, it accurate and fast for most work. Once it was registered to the new, old SB.it found a home.... jim
 
Remember,
You will need a tool to put on the OD of the jaws when you are truing it ID and vise versa.
Lee, I will ship your stainless Monday. Did you send me an address?
 
Butch, if you use the ring on the out side of the jaws you are tight on the back side of the threads on the scroll? jim
 
I seem to remember someone writing about cutting a circular groove in the nose of partially opened jaws and inserting a bearing race so that the chuck could be tightened inward as before grinding the inside of the jaws. Has anyone else heard of this?
 
I have wedges made that go between the jaws and you tighten down on them........then grind away.. jim
 
Well Hell! I hate to buy a bunch of gizzmos just for one chuck. maybe i need to just figure on getting myself a back plate for this Bison or buy a better set true chuck? Maybe ill catch one on e-bay. I wish i knew the quality of the Bison i have here in the shop already. What little info i have found on them, doesnt sound like it will be much better than the import that came with the machine. Seem like .003 runout is a fairly common standard for chucks under 5-600 bucks. All in due time i guess. Thanks men! Lee
 
I'd check the runout with a few different sizes of ground rods, to see if the runout was in the same location in regards to the chuck.

If it is, and you have a backing plate on the chuck, you can remove the chuck from the plate, turn a little off the registering surface, reinstall the chuck onto the backing plate, snug up the mounting screws not quite tight, use one of the ground rods, indicate it in by gently bapping the chuck body around with a soft faced hammer, and then tightening everything down when things run true.

Of course, this will only help if the chuck runout is the same when the rod is indicated in at the headstock as it is out at the end of the rod toward the tailstock.

If the measurement is greater out at the tailstock end than it is close to the headstock, I'd think grinding would be the way to true things up.

Also, I've always heard that the "correct" place to use the chuck key is in the socket directly by the brand emblem that is usually on the face of most three jaw chucks.

I have no idea if this has merit or not...
 
When I was an apprentice, all the lathes had 4-jaw chucks. You learn to dial in work fairly fast, use two chuck keys opposing, and you can chuck any shape part very fast. This also keeps untrained operators from useing the lathe. In shop at work, as part of the interview process, I have someone chuck up in 4-jaw, turn a diameter and cut a thread. This weeds out a lot of untrained people.
 
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simple way to put pressure on the jaws

One simple way to put pressure on the jaws for truing:

Drill a hole in the front of each jaw - 3/16" or 1/4". Insert a pin in each hole & tighten on a ring to put pressure on the jaws.

Using the tool post grinder to true the jaws is done to remove "belling" where the jaws are worn on the outside from chucking tapered barrel blanks in the 3-jaw chuck. It may give the jaws less runout, but you're still at the mercy of the precision of the scroll gear in the chuck.

I belled one when I was young & foolish - now I put a piece of copper wire over the barrel & chuck on that. It seems to work for me, but YMMV.

Regards,
Ron
 
With a little thought most any three jaw can be made Set True.
If the inset in the back of the chuck isn't deep enough, it can be
bored deeper so you can drill and tap the chuck for set screws to push against
the back plate.
I have also made the back plate larger than the chuck, with the inset in the
back plate deep enough to have the set screws in the back plate to push
against the chuck.
I actually prefer a four jaw to a three anyway. Kenny
 
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