Three Jaw Chuck--Tighten All Three Sockets?

[A.K. Boomer]

Hardened steel has the same elasticity as unhardened steel. It is a material constant.

Technically not so - 5% is after all 5%

also, keep in mind about the high load contact points and conformation there of, hardened resists deformation so it's a double wammy worth mentioning when picking apart details...

https://www.machinemfg.com/elastic-modulus-stiffness-strength-and-hardness/?utm_content=expand_article

[The Metal Butcher]

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...

Hardened steel has the same elasticity as unhardened steel. It is a material constant.

[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...

[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...

[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

[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

[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.

[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.

[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]

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

[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. 😁

[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

[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.

[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.

[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...