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.
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.
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.
The original 4-jaw is an old-style design however some people like it
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
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):