DoN. Nichols wrote:
According to :

DoN. Nichols wrote:

[ ... ]

Note -- he was wanting to get a three-jaw chuck with soft jaws.
The general practice is to have the diameter of a three-jaw chuck half
the maximum swing over the bed.

I didn't know that. So then as I was beginning to think, one would not
be able to take full advantage of any chuck that was over 3-1/2".(I was
only using that 5" as an example of the size that the lathe would
take). Here's another 5", 3-Jaw they advertise as being compatible with
the lathe we have:
http://www.littlemachineshop.com/pro...ProductID=2345

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).

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.

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.

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. 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.

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.

Darren Harris
Staten Island, New York.