According to Bruce Barnett :
(Nick Müller) writes:
Bruce Barnett wrote:
I'm interested in machining thin disks - about 1 1/2" in diameter by 1/16".
What machining operations do you intend to do?
Hollowing - for the most part, starting from the middle out.
So one disk will nest inside a second disk.
Hmm ... while the Taig pie-section soft jaws will work on this,
what I would think would be the best is a step collet, except that they
are rare on anything other than jeweler's lathes.
Or -- some soft collets with fairly large diameters -- but those
seem to be offered in 5C size mostly.
------------------------------ Pot Chuck Start ------------------------------
Or -- you could *make* a form of "pot chuck". Given the size of
your machine, I would suggest starting with a piece of brass or aluminum
somewhat larger in diameter than the larger of your workpiece diameter
and your spindle nose diameter. (They seem to be somewhat similar in
this case, though I'm not sure, not having seen your lathe.)
Anyway -- in a normal 3-jaw chuck, machine it to fit on the
spindle nose, and drill and tap it for the needed studs so you can mount
it directly on the spindle nose.
Mount it on the spindle nose, and mark it so you can always
replace it with the same stud in the same spindle flange hole.
Then, machine the ID a bit (say 1/8" to 1/4" smaller than the OD
of your workpiece, and perhaps 3/4" to 1-1/4" deep. Then machine a step
on the outer end just barely large enough and deep enough for a slip fit
of your workpiece.
Then, turn the OD down to perhaps 1/4" diameter greater than
your workpiece diameter, and down to the same depth that the inner bore
reaches.
Then, remove it from the spindle nose, and use a saw (a bandsaw
if you have it, otherwise a hacksaw or a slitting saw in a milling
machine.
Restore it to the spindle nose (being careful to use the same
stud per hole that you used when turning and boring it. Slip a
worm-geared hose clamp over the OD, place the workpiece into the ID, and
tighten the hose clamp to grip the workpiece.
Hmm ... you may want to drill a hole in the side of this to let
you reach the back of the workpiece to nudge it out if there is not
enough to grip.
Of course, you will have to make a different one for each size
of workpiece, but it should give you a very repeatable workpiece holding
system for this rather specialized task.
The pot chucks which I have seen in use were held in the 3-jaw
chuck, but that was on a much larger machine than you have.
------------------------------ Pot Chuck End ------------------------------
The second operation I'd like to do is to add a different metal around
the rim of an existing disk. I can see using two mushrooms for part of
the process.
I'm having a bit of trouble visualizing what you are describing
here -- especially the "mushrooms". If you intend to fit it to the
outside of something like a coin, without it extending beyond the
thickness of the coin, what I would suggest is another pot chuck for the
final OD of this, so you can bore the metal out to just too small to fit
(perhaps 0.001" too small, or a bit less.) When it is made, place the
coin (or coin equivalent) on a cold flat steel or cast iron piece, heat
the ring to an uncomfortable temperature (which temporarily expands it),
and drop it over the coin, using something like a piece of wood to hold
it down around the coin until the temperatures equalize and the ring
shrinks into a firm grip on the coin.
Good Luck,
DoN.
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