? Phase II 4 jaw chuck

Travers has a 6 inch 4 jaw chuck that I am interested in. My lathe is a Jet
9X20 with a 1 1/2 inch spindle. The 4 jaw has a 1 1/2 through hole and
I am wondering if there is any chance of interference when I put a back
on it. I assume (I know) that the back will be thick enough to keep
the chuck away from the spindle. Or should I not be concerned.
Bill k7NOM
Reply to
Bill Janssen
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I'm not sure I understand your concern, Bill. The backing plate for your chuck will have a hub that contains within it the proper thread for your spindle. The hole in chucks tends to be larger than the hole in spindles so you can chuck up larger diameters as deeply as possible in the chuck. As long as the hole through the chuck is larger than the hole in your spindle, and the backing plate is large enough to fit that particular chuck, I can't imagine where you'd run into problems, particularly if you're going to machine the back plate to fit. If I'm not understanding you correctly, please ask again, and try to specify your exact concern. Otherwise, I wouldn't be too worried about buying the chuck----buy it and enjoy.
Reply to
Harold and Susan Vordos
Ok Thanks. My lathe spindle is 1 1/2 X 8 and the chuck ( without backing plate) has a 1 1/2 hole. If the chuck had a larger bore then I would not have been concerned. I have to get a backing plate and machine it to fit. All seems well except I was wondering if the 1 1/2 inch bore was sufficient
The 4 jaw that came with the 9X20 is not very satisfactory and I was looking for something better.
Thanks again. Bill k7NOM
Reply to
Bill Janssen
If you got a chuck with a smaller hole in it, you could machine and thread it for a direct mount. I have see that done with flat back 3 jaw chucks on south bend lathes.
Reply to
Richard W.
The original 4-jaw is an old-style design however some people like it because it is so thin and also inexpensive. The hole in your spindle is around 3/4 inch. The size of the hole in the new chuck is fairly irrelevant. Make sure you verify your spindle thread before ordering a backing plate. Most 9x20's have a metric spindle thread. You might consider a visit to
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Reply to
You're not only confusing yourself over the hole size in the chuck, but you're confusing everyone with your descriptions of the spindle.
To be clear, your Jet 9x20 Lathe has an external 1-1/2" x 8 TPI threaded spindle mount. (The spindle internal through-hole is 25/32".)
As for the hole in the chuck, it has nothing to do with the spindle mount. When you make a threaded backplate adapter for your chuck, the threaded part of your spindle will be contained completely within the backplate. In other words, if you were to mount the backplate on the spindle (without the chuck) the end of the spindle should be less than flush with the face of the backplate (the mounting surface for your chuck). To get a better idea how the backplate adapter should be machined, take a look at the backplate on your 3-jaw scroll chuck. But note that most 4-jaw independent chucks do not use a full diameter backplate. It's more like a "plug" that fits into a recess in the back of the chuck. So your 6" dia chuck will probably require a max backplate diameter of less than 4". (As an example, my Bison 160mm [6.3"] 4-jaw independent plain-back chuck required a 82.55mm [3.25"] diameter backplate adapter.)
If you don't want to make a backplate adapter from scratch, I suggest you try one of these semi-machined backplate adapters from LittleMachineShop.com (size depending on your chuck requirements):
4" Dia:
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6" Dia:
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Regards, Michael
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