Where's the chuck in a chuck thread?

[john hobdeclipe]

Didn't we have a discussion recently about holding one lathe chuck in a larger lathe chuck, with some warnings about it maybe being a bad idea? I've been looking through the archives, and can't find it.

Or did I just dream this?

[thistle]

http://www.homeshopmachinist.net/bbs/showthread.php?t=20063

[JCHannum]

I can't seem to find it either. I do recall one.

There was one that resulted in a near serious incident when Christian Sokolowski had a chuck held in another chuck break while machining.

If I recall, the best advice is to use a stub spindle to mount the chuck rather than imposing forces on the chuck body by gripping it directly in another chuck.

[Evan]

http://homeshopmachinist.net/bbs/showthread.php?t=14823

[john hobdeclipe]

thanks

Thanks for helping me locate these threads.

I did a little job a couple days ago that required me to hold a small chuck in a larger one, and I feel that what I did was quite safe, but I kept thinking that we had discussed some dangers.

I had to grip a brass ring, about 7/8" inside diameter, from the inside so I could do some work to the outside of it. It was way too small for either of the chucks on my 10" Emco to get inside.

What I did was grip a little 3 inch or so 4 jaw chuck from an old Craftsman 109 lathe in the larger 3 jaw mounted on the Emco. But first I threaded a #2 morse X 1/2-20 thread adapter into the back of the small chuck, then ran a 3/8" threaded rod into the other end of the morse adapter and out the back of the spindle, and held it all together with a bushing, a hex nut, and another locknut.

This I think pretty well eliminated any chance of the small chuck getting loose from the big one and doing damage.

I'm glad I kept that little bitty chuck now.

[dicks42000]

Holdig chucks with chucks....

Yes, Christian did post here about a blow-up he had using his big lathe and a couple of chucks...sounded nasty.
If you have a copy of "Work Holding in the Lathe" by Tubal Cain, he covers using a small chuck held in a larger chuck for eccentric turning or offset turning. I've used the little 3 jaw from my Atlas 618 held in the bigger South Bends chuck for similar work, but only at low speed for threading....
Search the postigs as others have outlined here. Watch out for unbalanced forces due to the eccentric set-up, if that's what you're doing.
Rick

[rsr911]

Yeah that was me with the chuck explosion, it was spectacular and I've VERY lucky to have not been injured or even killed, I found peices nearly 100' away.

What did I do wrong?

1) No backing plate in the smaller chuck
2) Didn't realize the smaller chuck was cast, it broke along the jaw slots
3) Ran at high RPMS needed for the small work.

It was a small 4 jaw BTW. I've since bought a backing plate for my spindle for a larger chuck and machined it to fit a 6" 4 jaw. I bolted a 1" thick round drop to it and machined the OD then machined the face to fit the smaller chuck. I did this to provide the mass of a larger chuck as well as more leverage for spinning the chuck by hand when indicating a part. I'd be happy to take a picture of the new setup if you'd like. I find my self using it very frequently since the big lathe is nicer to operate as well as has the power to take much deeper cuts. I often have to machine solid SS rolls out of 4.25" stock with 1" shafts on each end. Since the rolls are required to be one piece with no welding I have a lot of material to remove which takes forever on my small Logan, I take off more than 1/2" at a time on the big lathe. Thanks to JC I've got a nice set of centers for the big lathe now so I rough in with the chuck then finish between centers.

[Kaferhaus]

I'd like to see the pictures of the "fix" you came up with.

Thanks

[rsr911]

I'd like to see the pictures of the "fix" you came up with.

Thanks

Well my good digicam is in for repair but I'll take a pic with my camera phone tommorrow and post it. Kinda bad resolution but you'll get the idea. The big lathe is a D1-8 BTW, the little chuck looks funny almost on a 20" swing lathe.

[john hobdeclipe]

Here's what I did

Here are some pix of my chucked chuck. The small 4 jaw is from a Craftsman 109, and has a 1/2-20 threaded hole in the back.

First two pix are of workpieces that are too small for the larger chucks on the 10" lathe.



In the second pic, the brass fitting is smooth inside and I can't grip it on a length of threaded pipe like I would if it were female threaded.

The next pic shows the little 4 jaw with #2 Morse adapter threaded into the back, the 3/8" drawbar, and the bushing that bears against the left end of the head spindle. A nut and locknut hold everything in place. I only need to tighten the large 3 jaw just enough to drive the smaller chuck.



I thought about this a bit before I tried it, and I think it is safe. If anyone can see something I've overlooked, let me know. I don't like the jaws of the big 3 jaw sticking out like they do, but I check everything for clearance before flipping the switch.

When I finish with the brass piece, it will look somewhat like this:



And it will top off a brass and wood lamp:

[S_J_H]

I made a couple model engine cranks doing the chuck in a chuck thing with my "lathe like" import 9x20.
Never really gave it much thought when I did it. Now that I look back at this pic I took when making them I don't think it was such a great idea.
Darned little cranks turned out well though.

[Millman]

John, I think you did one helluva job.