Proposal for "fixing" chuck - would this work?

[Thad Swarfburn III]

Problem : Old Emco Compact 8 three jaw chuck, jaws bellmouthed, finances don't allow for replacement.

Proposed solution:
1: Remove jaws and clean all oil from jaws and scroll (may require full disassembly of chuck).
2: Coat scroll and jaw teeth with slow cyano or possibly even PVA glue.
3: Replace jaws and chuck 20mm dia. plastic or wood dowel in chuck, tighten.
4: Wait until glue has set.
5: Drill and bore out remaining dowel.
6: Mount toolpost grinder on cross slide and true jaws in several passes.
7: Remove chuck and heat or rap jaws to break glue bond.
8: Disassemble, clean and remount chuck.

Would this work? I'm not looking for perfect repeatability from the chuck, but anything's better than what I've got now. Judging by the condition of the rest of the lathe when I got it, the scroll won't be so good.

I'm in NZ; even the cheap and nasty import stuff is expensive down here.

 

[goldstar31]

I think that this topic has been flogged and flogged in recent days in probably several forums( Four Eye)
At best, I would utter a qualified 'You must be joking'
Over the many years the topic has ben discussed and discussed by better than either of us.
I would say, either use a 4 jaw independent or collets.
What you can do is to build up the jaws again and grind them parallel to the long lathe ways.
You could make a set of soft jaws so that you get some semblance of repeatability- at ONE dimension each time you go to a new piece to machine.

As for some glue or other which is where you came in, I simply doubt that any glue would be capable of standing the tightening up operation. That does not mean that glues are useless or whatever. Far from it, however, there are plenty of epoxies etc that will work work wonders on your ( you said it) worn lathe.
My own - a Myford Super 7B- has a piece of Turcite building up the worn saddle. That, unfortunately, does not answer your question but is a note for future information.

Maybe, others will comment.

Norman

 

[maverick]

Thad,
Having used a chuck that only touched the stock on the inner end
of the jaws, I don't think you can hurt it much more. The glue may not
hold up to the shock of the intermittent cut when boring. Clamping on the ID of a ring to hold the jaws in place works well but may not give the desired "bias" if the chuck is well worn. If you've got nothing more to lose than
a hour of shop time, give it a try. Best of luck.

Regards,
Maverick

 

[n4zou]

Nothing lasts forever. Perhaps it's time to consider buying a new chuck.

 

[Dave Sohlstrom]

I have the same lathe and chuck that had the same problem. I chucked up a ring on the out side of the jaws and used my dremel flex drive in the tool post to grind the ID of the chuck jaws. Still have about .002" run out but that is about average for a 3 jaw chuck. If I need better than that I go to the 4 jaw or collet chucks.

Dave

 

[Ken I]

As a previous post said - you can't make it worse - give it a try. I for one would like to know how it turns out.

Unfortunately bell mouthed jaws are usually symptomatic of much worse problems - wear on the jaw guides and normally a very "drunken" scroll gear.

A bad chuck is a pain forever.

Good luck

Ken

 

[joegib]

How are you going to stop the superglue setting at some intermediate stage while you're doing the first reassembly — like leaving the chuck seized solid when you've only inserted one jaw? Have you got super-slow-setting superglue? PVA for metal-to-metal joints!

What's wrong with 'traditional' methods such as shown in this fixture:

Fixture

-- a simple circular disk with 4 holes drilled/bored in it?

Joe

 

[goldstar31]

What's wrong with 'traditional' methods such as shown in this fixture:

Fixture

-- a simple circular disk with 4 holes drilled/bored in it?

Joe

Read the Last line of the Fixture details SLOWLY
Read it again. It repeats what I wrote-
ONE DIAMETER.

 

[Charles Lamont]

If you read the original query carefully you will see that the primary concern is bell-mouthing.

If not too far advanced, this can indeed be corrected by grinding. However, I agree that glueing up the chuck is not the way to preload it.

This article explains how to do it:
http://www.homemetalshopclub.org/news/aug04/aug04.html

I have successfully used this method to cure bell-mouthing of my 4" Griptru. It restored a chuck that had become a complete pain (as a result of a certain hamfisted idiot allowing a job to be heaved out of it) into one that is now a pleasure to use.

For the job, I knocked up from materials to hand, a QC toolholder to take a die-grinder:
http://www.charleslamont.me.uk/images/iqc_grinder_holder.jpg

The jaws only needed a light tickle, but even so the job would have gone quicker if I had a larger compressor.

Don't forget to strip and clean everything after grinding in the lathe.

 

[Thad Swarfburn III]

If you read the original query carefully you will see that the primary concern is bell-mouthing.
<snip>
This article explains how to do it:
http://www.homemetalshopclub.org/news/aug04/aug04.html

That's an even better idea than mine, and why I asked!

Charles, the image link on your own site gave me a 403 forbidden.

In a perfect world, yes, I would buy another chuck. But as a Chinese one would run me nearly two days' pay (if I was working, which I'm not), AND I'd then get the pleasure of making a backing plate for it, it's time for a workaround. I do have a four jaw, and I made an ER32 collet holder when I worked on a CNC but haven't been able to stump up for the collet set to put in it.

Thanks for the help guys, I'll let you know how it turns out.

 

[abby]

On a three jaw chuck round work may be held outside by the jaws or tubular jobs can be gripped inside by the steps , for the first the jaws are tightened clockwise , for the second anti-clockwise.
It follows then that when the jaws are new the diameters of the steps are concentric to the inner gripping surface.
The inside of jaws will wear but the steps are comparatively rarely used and can be like new.
Chucking an accurate ring , I use the outer race from a suitably sized ball or roller bearing , will allow the jaws to be positioned for grinding without the need for elaborate jigs or set-ups.
I used this method for trueing my first purchase many years ago.
The "grinder" was a high speed vacuum cleaner motor with an extra long shaft for accomodating the fans.
I made strap clamps to fix the motor to the cross slide and mounted a small grinding wheel.
The purists will say everything done was wrong but the result was a vast improvement , and I used the chuck for years until I could afford a new set of jaws.

 

[Tin Falcon]

Thad:

What Dave said: I have the same lathe and chuck that had the same problem. I chucked up a ring on the out side of the jaws and used my dremel flex drive in the tool post to grind the ID of the chuck jaws. Still have about .002" run out but that is about average for a 3 jaw chuck. If I need better than that I go to the 4 jaw or collet chucks.

Dave

the better way would be to put a washer inside in the back and clamp down that way.This method you are putting forces on the jaws in the same direction as if chucking a part. but if the scroll is worn enough to make a big difference you may need a new chuck .
Tin

 

[joegib]

He, he, it seems that these chuck truing fixtures are not just the products of the fevered minds of hobbyists. NASA, no less, has posted a design:

NASA

OK, it's more elaborate than the ones referenced by Charles Lamont and I but in essence follows the same principles.

Joe

 

[MachineTom]

It has been my experience. that most bellmouth. chucks have badly worn slides. Chuck it and look for a good used one. I know nd is a small place, but that would be my first go

 

[Holt]

Feel free to use my idea if you like it:
http://www.homemodelenginemachinist.com/f28/i-stole-lathe-16864/index10.html#post180379

 

[goldstar31]

The big question is whether or not the scroll and the chuck body guides to the jaws or not were worn. If they were OK and the chuck jaws were only bell mouthed, I raise no issues.
I've done it all myself with a Mig/Mag outfit.
However, if the scroll etc were worn as well, what readings did you get for the obviously improved chuck.

A point about the A Series engine. I've re-worked the 12G295 and the 12G 296 A series heads but the question is how tough are the big ends and the crankshaft.
I was into such things way back in the 997 Mini Cooper days( before the 998) and whatever. That crank and the succeding 998 and 1098 ones were as weal as kittens and needed to be strapped or better. What have you done about this and perhaps the pins in the pistons? I went out to plus 60 in the bores in the Good Old Days.

Now running a very sedate BMW Mini Cooper, a Merc SLK 230 Kompressor and an Audi A4 Avant S Class (and a little High and Dri over in Spain)

Simply curious.