Dialing in a 3 Jaw Chuck

[Willy]

What's everybody's favorite method of eeking out those last few thou of runout when using a three jaw chuck?
Yes I know, that's what a four jaw chuck is for but sometimes when in a hurry and absolute precision isn't required (but always welcome ), what are some of the techniques you use in order to dial out an extra 2 or 3 thou less radial runout?

[Doozer]

If the scroll bushing is worn (sometimes old chucks are)
then you can tap the high jaws with a brass hammer
to try and move the material to a lesser runout condition.
Of course, long parts you have to "aim" on to center
by tapping in the long end.

--Doozer

[Doozer]

Long ago, they used to make 3 jaw independent chucks.
Special place in hell for the guy that invented those.

_D

[old mart]

I always leave a little play in the chuck to backplate register. That is the poor mans way of simulating a set tru chuck. In fact, I would rather do the fine adjustment that way and would not want a set tru chuck. My chucks are held onto the backplate by 6 screws for security rather than the 3 normally used. The little 100mm PB chuck in the picture was picked up NOS and had the common rear mount 3 threaded holes. It was stripped and cleaned after the front mount holes were produced. A little chuck is so useful for small jobs.

[David Powell]

I sent my 3 jaw independent off to hell ( AKA Lasco steel remelters ) as well as cursing the inventor after wasting an hour trying to set a round piece to run true.
Regards David Powell

[Doozer]

I sent my 3 jaw independent off to hell ( AKA Lasco steel remelters ) as well as cursing the inventor after wasting an hour trying to set a round piece to run true.
Regards David Powell

I know, right ??? ! ! !

-D

[wierdscience]

Buy a new Bison, use the master pinion only, (they are marked with a -0- next to them or a ')forget the other two exist, throw the old chuck away.

[J Tiers]

I just use the four screws provided.....

[Doozer]

I just use the four screws provided.....

In Frankenstein's neck ?

-D

[oxford]

I’ve done it with shim stock under a jaw or 2 if needed.

[BCRider]

Long ago, they used to make 3 jaw independent chucks.
Special place in hell for the guy that invented those.

_D

And I'd be applying one of the pitch forks myself. I can't imagine anything more hellish!

For small parts needing secondary operations on the other end after being cut or parted off I have a small 4 inch 4 jaw with a stub that I grab in the 3 jaw. It's darn handy.

I like the idea of the set screws against the undersize locating collar as well. But mine isn't set up for that.

[A.K. Boomer]

In Frankenstein's neck ?

-D

no - he means a real three jaw, one that's quick as can be for production same as a 3 jaw yet has separate 4 screw adjustment dial in's for accuracy throughout the entire scroll range,

set it and forget it - until you get to the next size piece that is and it throws everything off all over again... lot's of times not critical enough to matter but when it does you don't have to go butchering your jaws with a hammer trying to set them into the material more or whatever it is your talking about...

[Paul Alciatore]

I built the "true set" feature into my back plate. I tighten the work in the jaws. Then I loosen the bolts holding the chuck to the back plate. Then I dial it in with the four set screws in the back plate. Tighten the bolts and done.

In the past and with three jaw chucks that did not have this feature I used (tried to use) aluminum foil for shims on the high jaws. One thickness of household aluminum foil equals 0.0007". The foil can be easily folded on the jaws so it stays put. And it can be tossed out after one use. This technique can be problematic because adding shims on the jaws will change the effective diameter of the part and the scroll, when tightened, will come to rest at a different position. Also the part moves by at least a small amount when the jaws are loosened to add the shims.* So you are shooting at a moving target. This will not be a problem with accurately round stock or parts, but with other stock or parts it can be very problematic. So, sometimes this works and other times it doesn't. True-set style chucks do not suffer from this problem because the centering is done after the part/stock is tightened in the jaws.

* Yes, I know you can mark the position of the work vs. the jaws. But without a very small mark AND A MICROSCOPE, returning to the initial position is not guaranteed. The part/stock WILL shift when the jaws are tightened again.

[A.K. Boomer]

Willy I'll give you something to try that has given me mostly positive yet mixed results along the way, try a different phase chuck key receptor than the one you just used previously --- scrolls have play just to be able to function, they also have elasticity --- loading them from a different direction DOES indeed have varied results on the jaws depending on what one was used, usually the cheaper chucks without the 4 screw dial ins have three different access key receptors - hey maybe just for this reason? cuz the more expensive chucks that iv used (with the 4 screw dial ins) only have one key receptor...

[J Tiers]

In Frankenstein's neck ?

-D

it's a Buck adjust-tru.