In article ,
Ken Grunke wrote:
rhncue wrote:
I picked up a jet 12x40 bench lathe today. It was manufactured in 1983.
It appears to be in fairly good shape however the chuck and backing plate is
missing on this lathe. It did come with turning plate. My problem is that I
have an 8" chuck and backing plate with a 2 1/4"x8 mounting hole but it
doesn't go on the jet. It appears the jet is a 2 3/8" hole but it is an 8
thread where as all the backing plates I've been able to locate in 2 3/8ths"
are a 6 thread. Is there anyone on this forum who has had any experience
with these backing plates or have any idea where to acquire one?

Sounds like an easy turning job to me, enlarging a 2 1/4" x 8 backing
plate to 2 3/8" x 8--all you need is a metal-turning lathe with
threading capabilities, and a faceplate.

Or -- if you can do so for less -- get blank plates, perhaps
with a 2" unthreaded hole (or smaller), or with no hole.

Set it up on the faceplate, clamped in place with spacers
between the faceplate and your backing plate to be, so you don't cut the
faceplate itself, tap it to center and clamp it down hard. Then drill
the center, bore out to the proper ID, and internally thread.

But before this, set up to measure the thread pitch diameter of
the spindle (3-wire method, unless you have a pitch diameter micrometer
of the right range). Otherwise, as you get close, you'll have to keep
unthreading the faceplate and backplate combination, reversing it, and
testing it for fit on the spindle nose. With that big a pair of plates,
this will get old fast. :-)

Once you have it properly threaded, and the register cut, mount
it, and turn the mounting face flat, and true the OD, then turn the
necessary step to center it to the lathe chuck, and mount as necessary.

Among other possible sources, Bison makes blank backing plates,
as well as pre-threaded ones, and New England Brass and Tool sells them.
(I've bought the pre-threaded ones from them, as I only needed to fit a
2-1/4x8 spindle which was supported. Yours *might* be, or might not.
But the unthreaded blanks are cheaper, of course. :-))

At least the Jet import lathes can cut their own spindle thread.
Some of the others have a metric spindle thread, but are sold here with
the gearing to cut only Imperial threads, so you are stuck having to buy
chucks or backplates from the vendor. :-)

Good Luck,
DoN.
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