According to :
First off -- I got two e-mails from you today -- with the old
return address which your usenet articles show. I am not going to
bother typing answers to them, only to have the answers sit for a week
and then pop back up as undeliverable.
*If* you posted as well as e-mailed, I'll try to answer here in
the newsgroup. If you didn't -- then take this as a reason to not send
me e-mail copies of usenet postings, or e-mail with bogus return
addresses.
DoN. Nichols wrote:
[ ... ]
One can use larger chucks, but the added weight hastens wear on
the bearings.
And you have to be careful that the extended jaws do not hit the
ways, or the side arms of the carriage, if your carriage has them.
IIRC, it does not.
Note that photo on that web page includes the second set of
reverse jaws for gripping larger workpieces. But, because of the steps,
they can't grip a great length, so you need support (steady rest) once
the length of the workpiece exceeds a certain percentage of the step
length.
[ ... ]
"X" inches is the overall diameter of the chuck body. To that
must be added the extension of the jaws when they are adjusted to hold
larger workpieces.
This is just the sort of stuff you never read in catalogs. So I now
have to figure out what is the "largest" chuck that I could use on my
lathe to hold the "largest" work pieces.
Part of that is a function of how long the workpieces are. And,
whether you have a steady rest to help support the workpiece.
I'm thinking more in terms of diameter.(Flat stock).
O.K. For that, it should suffice. Obviously a 4-jaw
independent is what is needed.
The ones which can accept soft jaws are typically two-piece
jaws. A hardened set of master jaws which remain in the chuck, and sets
of jaws which bolt onto the masters. What typically comes with the
chuck is a hardened set of top jaws. Soft jaws are available to fit the
same master jaws. They can be either aluminum (really soft jaws), or a
mild steel (which is more common, except in the little 3-jaw chucks for
the Taig, which are non-standard in several other ways as well.
I guess machining a new set of jaws out of Aluminum is not plausible.
:-)
Why not? Where do you think the jaws come from? Actually, the
Taig soft jaws are easier to make than most, because there is not the
middle step to give precise location which is present on most master
jaws. All the Taig jaws have to offer are the screws which hold them
on.
What I meant was that I don't think he has the equipment for machining
the jaws himself.
"He"? Who else came into this thread?
If you have milling attachments for the lathe, you can make soft
jaws -- especially the ones for the Taig with its simple mount.
Note that the "Pie" jaws are actually made from electronics
heat-sink extrusion, which is why all the fingers.
Now -- This applies only to the top jaws to go onto existing
master jaws. For making complete jaws from scratch, you need to
consider how you are going to make the scroll teeth on the bottoms of
the jaws. Each of the three jaws has the teeth at a different offset,
so the three jaws wind up close to center when the chuck is assembled.
Sounds like a CNC job to me. Or a job for an experienced machinist.
It used to be done with the jaw blanks mounted on a fixture on
an index head which was geared to the X-axis leadscrew on a milling
machine. The index head would turn fairly slowly (from a power feed),
and the gears would turn the leadscrew to provide the proper feed per
turn. A small endmill would cut the spiral threads in the back of the
jaws. (Quite probably, the fixture would hold two sets of jaws at once
to improve production and to minimize the amount of time spent cutting
air.) A similar setup would machine the scroll plate for inside the
jaws. The jaws would be shaped, and hardened, and then the two sets of
scroll teeth would be lapped -- either together, or on separate
fixtures. This would shape the teeth to allow handling the varying
radius as the jaws close or open.
Yes -- it could be one with CNC now -- but it may be more
economical to use the old machines if they still work well.
What I'd do is make a hard wooden holder with a hole that would be the
same diameter as that of the disks, and the appropriate depth(and a
small hole all the way through the center so that glue will dry when
used along with a press fit of the disks into the holder. The holder
would then go into the normal chuck.
Note that wood, even hardwood, changes dimensions with the
ambient humidity. You can't keep any kind of precision with wood.
It shouldn't be too extreme.
A friend made a copy of an old instrument called a
"hudry-gurdy". Not the barrel organs, but rather a stringed instrument
in which the strings were bowed by the rim of a wooden wheel. Well, the
problem was that as the wood dried out, what had started with a nice
round wheel shrunk differently along the grain and across it, so it was
pressing harder on the strings during part of its rotation than during
other parts. It could not be kept in a shape good enough to produce a
steady sound.
I finally machined one for him from plexiglass, which would not
shrink. The only problem was that I put too good a polish on the rim,
and it would not hold rosin to drive the strings. :-) He solved that
with a strip of wood veneer with a diagonal join.
So -- yes, wood *does* shrink enough to be a problem as it
dries. The original ones were almost certainly made with wood which had
been dried for decades before being shaped put to use, not modern
kiln-dried wood.
Especially since the work is not big and
heavy. And a facing operation will not pull it out of the holder. But
one can use glue if a small hole is place in the center for ventilation
so the glue will dry.
But if it is still an issue then an option is Delrin which doesn't soak
up moisture and has excellent dimensional stability.
Delrin, a set of radial grooves from the center hole to near the
outside diameter, and a vacuum pump sucking on the center hole to keep
the workpiece in place.
But probably not for stainless steel. :-)
Or perhaps brush some liquid insulation around the perimeter of the
disks and let dry. The kind used on electrical wires. It peels off
easily.
I doubt that it would hold very well, but you are welcome to
try, and report back on the results.
It's job would be to just keep the jaws from damaging the workpiece.
Oh -- that is what aluminum soft jaws are for. When they are
machined in place in the chuck (in the lathe) the shape is such that
they will match the curve of the OD of the workpiece, so there is no
sharp edge trying to indent the workpiece.
Enjoy,
DoN.
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