"Lew Hartswick" wrote in message
m...
Karl Townsend wrote:
...
Joe Gwinn
I just made a set out of 6061 Al at school on Thur. Havent
used them yet but need them to hold some threads without
"buggering" them up. Havent figured out how to hold the
jaws in compression while threading all the way through
the soft jaws yet.
...lew...
In such a case, I like the jaws to project inward, beyond the surface of
the master jaw. Grip your spider (or piece of stock) on the master
jaw, allowing full access to the soft jaw. Works fine, Lew.
...

I had a project where I had to make four inch high jaws and the part
had to fit down inside the chuck (NMTB tool holder). So I drilled and
tapped 1/4 20 holes in the top of the jaws. Then a plate to bolt on. I
liked this method so well that i made a special plate to fit all sizes
with spiral slots and now I always bore my jaws this way.

Karl


Karl I don't see that in my head. Can you post a pix somewhere of
that?
I want to hold a long piece of all-thread and work the end / cut off
thread out and repeat so there is no place to put a support to clamp
on. I'm thinking three small pieces sort of between the corners of
the jaws.
Harold, I'm not sure exactly what your describing but "maybe" a
sacrificial piece that the the master jaws clamp on before the
soft ones touch that I can then drill through and tap then remove????
Yes??
Thanks.
...lew...

Yeah, that's it Lew. I don't recommend drilling and tapping, however.
You'll have less than good fortune accomplishing your mission because of the
interrupted cut. If it's possible, bore the hole for a round and straight
result. The exception might be if you can get the jaws all but touching.

Do consider holding the material by the major diameter instead of threading
the jaws, too. Unless your application is critical of concentricity, p.d.
with the work you'll do, it's a lot of trouble to go to for little, if any,
gain. You'll be duly pleased with gripping the major under all but the
most trying of circumstances.

Long ago I did a series on soft jaws and how to apply them. In one of the
articles I talk about a spider, which is used to bore soft jaws. It
avoids the hunt for a specific size of material for each time you need to
machine the jaws, with the added benefit of being able to true the jaws by
removing only a few thou, even when the profile may not be perfect for the
application. It need not be, not as long as you can achieve a respectable
surface area.

Regards the spider, if you're interested, they're real easy to make. Using
a fairly large nut (1" or so) , drill and tap at 120 degree intervals for a
socket head cap screw. Mine are 5/16-18, for use in an 8" three jaw.
Locate the three tapped holes near the edge of the nut, so you can get the
spider as far back in the jaws as is possible for machining the jaws. You
can even locate on the master jaw, allowing for through boring.

If you're interested in reviewing the posts, I'll provide links. Lots of
good reading, with pics to help in the descriptions.

Harold