Dialing in a 3 Jaw Chuck

[Doozer]

I don't think Willy has an adjust-tru.
He has a conventional 3 jaw scroll.

-Doozer

[lakeside53]

hell? Heck I have a 4 jaw scroll plus separate jaw adjust. Love it!

Back to the Op... I don't. I deal with the runout All ops without dismounting, or use a set tru ot 4 jaw or collet, or...

[LKeithR]

...I deal with the runout All ops without dismounting, or use a set tru ot 4 jaw or collet, or...

Exactly! A three jaw chuck is just fine for probably 99 per cent of what most people do. Get a good one
and use it. If it's not good enough go to a 4-jaw, collet chuck or soft jaws. Tinkering with a 3-jaw is a complete
waste of time...

[Doozer]

hell? Heck I have a 4 jaw scroll plus separate jaw adjust. Love it!

...

AKA combination chuck.
I have one, a Wescott brand I believe.
Has a strange nose thread.
1-3/8 8tpi if I remember.
Might fit an 8" SouthBend or something off the wall.

-Doozer

[Willy]

Thanks all for the feedback.
Yes it is a conventional 3 jaw, not an adjust-true type. And yes I do keep all critical operations on this 3 jaw to one-setup operations. Actually it's only out .0015"-.002, consistently. Who knows it may just be one jaw, I'll look into it later, but no complaints as far as 3 jaws go, don't think I'll gain much.
I had used the tricks outlined from some of the posters to this thread before with varying degrees of success, just not repeatable enough for my liking hence the question to see if I missed something in knowledge or technique.

I do have four jaw chucks to lean on if needed and know well in advance when I should require their repeatability should I have to remove the workpiece from the chuck and have to place it back into the chuck. The four jaw was the only chuck I used for a number of years due to this shining quality and yes once used to it, it does not take long to obtain consistent and repeatable results.

The project I was working on the other day was a muzzle brake for a rifle, so I did know before hand that concentricity was of paramount importance and all operations, boring, threading, etc. were all done in one setup without removing the muzzle brake from the chuck to ensure that the bored holes and threads were concentric with the rifle barrel that it will be installed onto.

I always plan ahead trying to think of the possibility that I may have to remove the part and then scramble to regain concentricity. This is why I asked, because I did this project in my 3 jaw and I kept wondering...what if?

[Doozer]

For gun work, I would think you would want to start using a 4 jaw.

-D

[A.K. Boomer]

.0015 to.002 is close enough for me to say that yeah you have at least a 66 and 1/3 chance of at least improving your situation some IF you have a 3 receptor key chuck,,, not too shabby of a chuck Willy certainly not a dud...

[Willy]

For gun work, I would think you would want to start using a 4 jaw.

-D

I usually do, but the 3 jaw was on there already...yeah I know, lazy.
Not to worry though this is for one of my rifles so I'd be the first and only one to eat it. But I'm fussy as hell for checking the finished product on this type of work, if I'm not totally satisfied it goes into the scrap pile. Once that trigger gets pulled there's no calling that bullet back.

[Willy]

.0015 to.002 is close enough for me to say that yeah you have at least a 66 and 1/3 chance of at least improving your situation some IF you have a 3 receptor key chuck,,, not too shabby of a chuck Willy certainly not a dud...

Yes, it's been a good little chuck, can't complain about 2 thou at all. For most of the work I do use it for it is above the level that I need...which is often closer to twenty thou.
A half inch drill motor held in a vise as a lathe with an angle grinder or a file in one hand if accuracy was important.
Never forget your roots.

[lakeside53]

I always plan ahead trying to think of the possibility that I may have to remove the part and then scramble to regain concentricity. This is why I asked, because I did this project in my 3 jaw and I kept wondering...what if?

If you mark the part and jaw with a sharpie, often you can take it out and get it back with pretty decent accuracy. Try different pressure on the tightening chuck key to move it a little until it dials back in.

[J Tiers]

When I did have the problem you describe, I would shim the jaw that had the problem (high side jaw). That would do the job. That was back when my only 4 jaw was too bellmouthed to mess with for anything accurate. I replaced it pretty soon.

[old mart]

Marking with a sharpie won't work if you are turning the work around in the chuck to machine the other end.
Paul Alciatore and myself both have the solution, but are ignored for no good reason.
Set tru type chucks are an extremely expensive work around which the chuck manufacturers would like everyone to spend their money on.

[Willy]

Marking with a sharpie won't work if you are turning the work around in the chuck to machine the other end.
Paul Alciatore and myself both have the solution, but are ignored for no good reason.
Set tru type chucks are an extremely expensive work around which the chuck manufacturers would like everyone to spend their money on.

Not ignored at all, on the contrary I think you and Paul's idea of the poor mans set tru is an excellent idea that I'll very likely incorporate into the rough casting backplate I have laying on the bench. Just have to figure out which chuck I'll be mounting on it.

Sorry I may have been remiss in acknowledging your ideas but they certainly have been noted, as were all of those that were suggested.
A big thank you to each and everyone who took it upon themselves to offer assistance.

The solution I had hoped to obtain was to be an in situ solution hopefully. All the other ideas that were suggested I have already used, with varying degrees of speed and success. The 3 jaw that I have been using is almost a shrink and press fit to it's backplate and it is close in runout and repeatability so I'll likely leave it as as.

[old mart]

If you do try the poor mans set tru, the register clearance only has to be about 0.010", so the chuck will be able to move 0.005" from the centre line. The screw hole tolerances should allow this ammount of movement. I have at least 6 three jaw chucks with intentionally loose registers and most of them have 6 screws holding them on the backplate, 2 using front and back mounts 2 using front mounts and 2 using rear mounts. The exception is the serrated jaw chuck which usually has its soft jaws machined, so a loose register is of no benifit. If you only have one chuck, then a four jaw independent is always the best option, they do not need loose registers to dial in perfectly.

[Willy]

Thank you old mart for the additional tips and insight, greatly appreciated. One heck of a good idea to gain additional concentricity out of those 3 jaw chucks.
Now we can only hope that my next candidate for incorporating this idea has jaws that are true and even.