Can you mill down the jaws on a chuck, or are they too hard?

[J. Elliott]

Fellas,

I've got a lathe with an L-00 spindle. It came with a beat-up old English chuck. Its L-00 adapter is worth more than the chuck, and I'm using the adapter to fashion up a mount for the replacement Bison Set-Tru I've found from a fellow here on PM.

So, now I'm curious what I can do with this old chuck. It isn't loose, but the jaws don't hold true anymore. They look like crap and the chuck has 20 thou of runout. And I think my homemade remedy for truing them made things worse!

It might fetch $20 on eBone, but I don't even want to bother. I'll have to mention I tried truing the jaws and it might not even bring $10. Nah.

Today I had a radical thought. The master jaws are one piece deals. Mill 'em down flat, I mean get rid of the steps, and fit aluminum soft jaws to the masters. They won't be serrated, so I'll have to dowel pin them or something to get a repeating seat location along with bolting them on. Basically, I'm talking about fartin' around with this chuck.

Are the jaws too hard to machine? How do I cut them down to a flat top surface? Can I endmill them on the mill? Should I chuck up something while milling, so that the jaws are cut with pressure on them similar to running condition? Threads to hold soft jaws on fine or coarse?

If this works, it would be great to have a chuck I can outfit with soft jaws. The chuck still fits on the L-00 adapter good-n-tight, and seems to scroll fine as well. If this soft jaw idea works, it might restore this thing to a degree of functionality.

 

[HuFlungDung]

Do any welding? An old chuck turned into a "positioner" is a good retirement for a chuck. Mind you, we do a fair amount of welding, but an old slopped out chuck has served my shop very well for many years.

Jaws are pretty tough slugging to mill through, IMO. They might even be through hardened, which makes drilling and tapping holes impractical.

The safety aspect of bolting on 'smooth junction' jaws would concern me a little bit. A fair bit of force is exerted on the jaws, and will put a lot of shear stress on those bolts. The repeatability of even the soft jaws may not be good enough to be useful, if they keep slipping and working their way outwards.

 

[BadDog]

If they are soft enough to mill, they are soft enough to tongue-n-groove. Using American Standard would allow options for commercial top jaws. BUT, I think they are far to hard to mill. Perhaps sinker EDM? Or even wire from the side getting part of the profile, then grind the rest?

I rehabed a sad old 3 jaw Buck chuck using a home made tool post grinder (Dremel) by clamping it on an "average" size piece at the back and grinding the bell mouthed 1-piece jaws back straight. It's still no top quality chuck, but makes a dandy holder for stuff that needs abrasive work without corrupting my nice PB 3 jaw. It also has soft jaws (and of course masters) which allow other options should I choose to use it...

 

[Limy Sami]

Most hard jaws are through hardened, I did it this way on an old Pratt.
I got them ''let down'' as my guy put it, annealled in a muffle furnace and they machined beautifully, if a little tough!!
I was going to get them rehardened after I'd cut the tenons......... but sorta never got round to it, and never regretted it either.

Take care. Sami

 

[gwilson]

You could heat them up red hot in an electric furnace,wrapped in stainless foil.Let them stay in the furnace overnight to cool down slowly.You could even put them in a wood stove with a good hot fire.let it burn down till cool.I've done this,worked just fine,provided the jaws are not made of some special stuff like air hardening,which they most likely aren't.Jaws may only be hard for the outer 1/16",unless they are very small jaws.

 

[allanjs]

J.Elliot,

I have done just what you are talking about.
First I used an abbrasive cutoff saw to remove
the jaw steps. Then annealed the jaws as they
seemed to be just surface hardened. Then face
cut them and milled a groove in them. Then drilled
and tapped 2 course thread holes. I then made
soft jaws from mild steel with a matching tongue. They work perfectly. Keep a print or sketch for making future jaws.
Al

 

[WizardOfBoz]

Hi,
There are two types of bellmouthing. The first is wear on the jaws themselves. The second is wear on the grooves and slots in the chuck body and the jaw bases. If the former, you can set your chuck up in the lathe, use some technique to simulate having something in the ID of the chuck (there are several techniques, some discussed here), and use an internal TPG (or if you are clever, a Dremel mototool) to get the jaw edges parallel. Or at least, so they say.

Wear on the slots is tougher. I tested my old Buck 6 jaw by laying it flat face up on my lathe bed ways (careful, now! A surface plate would work better), putting a test indicator on it, and watching how much the jaws rose when I tightened it on a workpiece. Should be less than 0.001 (!). Mine was kind of screwed.

For bigger checks, it is cost effective to hard chrome and re-grind the slots. Cheaper to find a new 6 jaw in the 6 inch size.

Good luck,

Jim