Small Lathe Chuck, but with a big bore

Hi All,

I'm looking for a smallish 3 jaw chuck about 6" with a 3" bore. I have this part that is flanged 6" on one side and about 3" on the other, we want to be able to chuck it flange out in the jaws. Going to bolt this on a mill table, so it doesn't need to spin, but the centering of a 3 jaw is really handy. I know they make plenty of clamping systems, but I don't know of one that self centers like a scroll chuck.

Though about a 4 jaw, but then I would be doing a fair amount of indicating, which is slow.

I was looking at a Shars chuck, because the jaws are replaceable, which would be nice in this application.

Looked at wood lathe chucks, but they appear to have similar issues, don't know enough about them.

Do they make something? OR can you bore out a 3 jaw, like bore out the entire center, I think the scroll is held in place by the outer edge generally and I think the bevel gears can be removed welded to a TEE like a big chuck key. Maybe get a cast steel one so I can weld to it.

Yes, I understand it will destroy the chuck for any other purpose. If it works OK I mount it to a plate to quick attachment and removal

Thoughts.

Thanks
Aaron

Aaron-M said:

Hi All,

I'm looking for a smallish 3 jaw chuck about 6" with a 3" bore. I have this part that is flanged 6" on one side and about 3" on the other, we want to be able to chuck it flange out in the jaws. Going to bolt this on a mill table, so it doesn't need to spin, but the centering of a 3 jaw is really handy. I know they make plenty of clamping systems, but I don't know of one that self centers like a scroll chuck.

Though about a 4 jaw, but then I would be doing a fair amount of indicating, which is slow.

I was looking at a Shars chuck, because the jaws are replaceable, which would be nice in this application.

Looked at wood lathe chucks, but they appear to have similar issues, don't know enough about them.

Do they make something? OR can you bore out a 3 jaw, like bore out the entire center, I think the scroll is held in place by the outer edge generally and I think the bevel gears can be removed welded to a TEE like a big chuck key. Maybe get a cast steel one so I can weld to it.

Yes, I understand it will destroy the chuck for any other purpose. If it works OK I mount it to a plate to quick attachment and removal

Thoughts.

Thanks
Aaron

Click to expand...

Let me start at "the end".

- I suspect your best way forward is TALL jaws on an otherwise unmodified chuck.

Tall enough that reversed jaws with a step to grip the work do not NEED a large bore because your boring bar, boring head (or wotever..) need not go that deeply.

Now.. as to the "why" of it? Just look around, see how a "scroll" chuck is arranged, internally.

The scroll isn't very wide "as it is".

To provide a 3" bore, presume a 1/4" more as the wall to support the ID of the scroll plate. You are at 1 3/4" on the inner edge of the radius of the guts.

To provide a 6" OD, presume a 1/4" less as the outer wall. You are at 2 3/4" radius for the OD of the scroll plate.

The active scroll "face thread" is now only one inch wide.

Can it be DONE? Surely.

But is it wise?

How much grip strength can that provide?

And for what life expectancy before worn, if not also damaged, to no longer hold decent TIR?

And what sort of mill only provides room for a 6" OD, anyway, if it can live with, for example, 10" and larger rotabs? (or can it, really?)

Bigger chuck, taller jaws?

You might not need to do ANYTHING "special". At all.

2CW

+ 1 on what Thermite said, .......take a 6'' (or more than likely even an 8'') 3J scroll chuck apart and you will see a 3'' hole just ain't gunna fly Wilbur.

There was a species of 3 jaw SC chuck combining large bore with small size. Instead of a scroll the jaws were driven by a cam ring. As the jaw movement was very limited, little more then enough to change workpieces, standard serrated base interchangeable soft jaws were used.

Presumably yet another device to speed up work on capstan lathes and help Piecework Pam keep her weekly income up to scratch.

Had one through my hands (maybe its still in the must have a clear out box) years ago. Even picked up a new set of jaws before wondering why the jaws hardly moved and stripping it to see what was jammed. Got inside and thought Hmmn, clever but will I ever use it. Rats! now I've gotta go and have a look to see if its still around.

I guess the contact angles in the cam ring, housing and jaw drivers were arranged so as to make things self holding like an MT taper.

I imagine a normal chuck could be reworked to use a similar style of mechanism. Bore out, fit an insert to keep the crap out, defenestrate the scroll, fix a plate on instead of the teeth and cut a matching three lobed form to drive the jaws. Basically one big tooth on the jaw to engage the cam rings. Its gonna be a bastard to assemble.

Fun project, for the somewhat insane, but hardly worth while.

Clive

I know the chuck you mean Clive - from way way back in the day - but what were they called ?

Limy Sami said:

I know the chuck you mean Clive - from way way back in the day - but what were they called ?

Click to expand...

On the shop floor probably "Bloody thing is always the wrong size." but I'm sure Herberts or Crown had a posh one.

Clive

Great,

That's what I was looking for, who sells American Standard Tongue & Groove jaws that are really tall?

Thanks

Aaron-M said:

Great,

That's what I was looking for, who sells American Standard Tongue & Groove jaws that are really tall?

Thanks

Click to expand...

Make them FFS.

Use some pie sections of aluminum, bolt them on, bore them to size.
The wider face of the inside will keep the work from getting cranked out of shape.

Tudor Chuck?

Not exactly sure what you are trying to accomplish....If its holding a 3" round vertical with a 6" flange at the top.....
If this is a dedicated job and the 3" is the same for all the parts....I would suggest tall soft jaws in the mill vise, bored to accept the 3" round...
Pretty simple and cheap....Could roll your own. Will be quite repeatable if done properly, and fairly rigid.
Cheers Ross

On edit:
If the round is long, perhaps a large angle plate with a Vee block attached (running vertical) and fitted with a chain clamp...

Might be a clearance issue tho, talljaw guys ? If he wants to sink the shaft part down into the chuck to save z travel .... I had a Forkhardt that had a pretty big hole, but maybe not that big.

Some sort of a collet ?

Pretty sure you could do this with those hydraulic expanding deadlybobbers but they aren't cheap, no sirree

TedinNorfolk said:

Tudor Chuck?

Click to expand...

Thanks Ted, but I have a 6 1/2'' Pratt Tudor and basically it's just an ordinary 3J scroll chuck.

EmanuelGoldstein said:

Might be a clearance issue tho, talljaw guys ? I

Click to expand...

Angle plate and Vee block/blocks and chain clamp will allow part to be down hard to the mill table, or hang it off the side or front or back ....
Can't get more head room than that....Me i would run it horizontal on the Deckel. (part in the vise ling ways in the jaws)..almost unlimited length acceptance.
Cheers Ross

The part is cast, so there is always a little variation from piece to piece. We don't want to machine the cast outer periphery of the 6" flange. The inner section is not straight and isn't idyllic to grab with a chuck. So we're looking at options to hold it at the flange centered best possible.

We're moving the part in house, we have a CNC BP conversion for thread milling so that's why space is tight, we want to fit as many on the table at a time without it weighing a ton. This just needs to hold it well enough for a mill cleanup and a thread milling operation. TIR of 0.010 on actual center is absolutely fine.

Just trying to solve this little piece of a bigger machining problem. Trust me I know, there are 1000 ways to skin the cat better, but I got what I got and I have to work within that envelope.

Thanks

Aaron

If 8" chuck fits the bill those are available with 3" bore.
ie (indian) example Buy Zither 3 Jaw Large Bore Standard Self Centring Chuck 200 mm 1003-2003 Online in India at Best Prices