Three Jaw Chuck--Tighten All Three Sockets?

[A.K. Boomer]

At the end of the day, the chuck itself is not accurate enough to make a lot of fuss worthwhile. "As accurate as possible" (with that chuck) is probably not very accurate.

Most, if not all, of the 3 jaw chucks I have use just one pinion anyhow. So I can say "I just use one pinion", or I can say "I use all the pinions on the chuck" and it means the same thing.

If it is important, I use the 4 jaw.

No - inconclusive - he just made the initial post and did not comment what type of chuck, so, at the end of the day it matter's what kind of three keyed three jaw chuck were talking about comprendo?

and if you only have one key then it's useless to even compare on this topic...

[Paul Alciatore]

Three jaw chucks almost universally use a scroll plate to close the jaws. This scroll plate rotates and the scroll pushes against ALL THREE JAWS at the same time. You can see some good illustrations of this here:

https://www.engineerknow.com/2021/03/3-jaw-chuck-mechanism.html

The tightening points are actually gears/pinions that are used to rotate the the scroll plate. Once the scroll plate is holding the jaws tight against some work piece it, the scroll plate is effectively LOCKED in position by the three jaws. BUT the pinions are still FREE to rotate a bit due to clearance between their teeth and the teeth on the scroll plate. They, the pinions, are NOT locked. No matter how tight the scroll and jaws are, the pinions are never locked. There is no "taking up" the backlash. They can always "rattle about", no matter how you tighten things. Or, at best, one or perhaps two of them may be jammed up by the tightening process. But never all three.

What happens is the scroll plate's OD and/or ID or both has a little bit of clearance between the surfaces of the body of the chuck. Ideally this should be zero, but that is not practical and any real-world chuck will have this clearance. So the scroll plate can move a bit side-to-side. And it is that side-to-side movement that you are controlling or trying to control with different tightening techniques.

I was taught that whilst you pull up the Chuck from a single drive socket that it was pertinent to take up the backlash on all three, as it’s better to have all three take the load and not have 2 rattling about, made sense.
mark

[A.K. Boomer]

What happens is the scroll plate's OD and/or ID or both has a little bit of clearance between the surfaces of the body of the chuck. Ideally this should be zero, but that is not practical and any real-world chuck will have this clearance. So the scroll plate can move a bit side-to-side. And it is that side-to-side movement that you are controlling or trying to control with different tightening techniques.

Perfect description, except i will add - "all the above with the having to have clearance issues" AND elasticity of materials...

[The Metal Butcher]

How do you know which one is the master ?

Bison chucks are marked.

Buck made it easier. Only one pinion.

If you need grip and accuracy, try to save the master for last.

Or, 4 jaw.

[BCRider]

It's almost certainly caused by one happening to move the scroll slop in the direction to counter the inherent runout from other causes, OR that particular one just having less slop overall.

It's odds on that the best will in fact change over time. If the scroll has slop then probably cutting forces can move it around, so you might want to do something about the scroll slop.

Well obviously there will be scroll slop. Both in the pinions to the crown gearing and in the center hole to the center boss. I'm thinking that this master pinion idea is mostly about biasing the scroll plate in the direction caused by the torque off the master pinion. That's going to shift the scroll which in turn shifts the final jaw locations. But it's enough to cause differences from pinion to pinion.

[Ian B]

If you're bothered about a 3 jaw holding a piece of round stock to within a few thou, shouldn't you be using a 4 jaw and a dial gauge anyway?

Ian

[The Artful Bodger]

.. just a guy who know's machines and equipment very very well.... .

It is times like this I really miss the late Sir John Stevenson. 😁

[DennisCA]

I always do all three and I find there's always slack on the two others after I tighten the first.

[Mcgyver]

All three is better. If you need it concentric, don't use the 3J. Think of how they work. You'll get the same tightness with a lot less strain one spot of the scroll if you use all three. Do I always, no, but the Q was what is the correct way.

[DennisCA]

In practice I only ever use the 3J chuck even for when high level concentricity is required. I have modified mine so I can loosen back plate nuts a little and tap it around until the part runs abso-friggin-lutely true. I use my 2 micron indicator and when I get 2-3 microns that's good enough for most things.

[J Tiers]

Yes to the issue of looseness in the scroll, mentioned back in post #10.

Each pinion will both turn the scroll and force it out of position if it can move. One may combine errors in such a way that at least for a while, it is the best.

But tightening each in turn will probably just push the scroll around slightly once the thing is basically tight. That might allow another fractional turn of the pinion, or not.

So much fuss and detail all oriented at not having to use that pesky 4 jaw chuck.

No - inconclusive - he just made the initial post and did not comment what type of chuck, so, at the end of the day it matter's what kind of three keyed three jaw chuck were talking about comprendo?

and if you only have one key then it's useless to even compare on this topic...

The "type of chuck" is virtually certain to be a 3 jaw standard scroll chuck. If you had a lathe that would be pretty obvious to you (IIRC you are quite proud of only needing a mill). What beside a 3 jaw scroll chuck has 3 pinions?

I am sure you meant "useless to comment", not "compare", but no , it is not.

[boslab]

In all honesty a three jaw Chuck on a lathe in work was “ unusual”, 4 jaw got put on and stayed there for the most part no one could be bothered to change the chuck, comments like how do you clock it in with a three jaw, true btw, plus an 18” 3 jaw?, I think not
my three jaw disappeared , I don’t miss it
mark

[JRouche]

" Three Jaw Chuck--Tighten All Three Sockets?"

I do. Just because I dont know any better. I will chuck the part up in one of the screws just enought to hold it. Then rotate the chuck to where the part seems loose and tighten the other screw. I am used to a four jaw so I treat the scroll chuck the same. Old habbit. lol JR

[Paul Alciatore]

Yes, all tools are made of RUBBER.

Perfect description, except i will add - "all the above with the having to have clearance issues" AND elasticity of materials...

[A.K. Boomer]

Yes, all tools are made of RUBBER.

No reason for getting that dramatic now - take a deep breath - rubber would probably flex inches with those kinda loads while hardened metal tenths of a thousand's of one...