"DoN. Nichols" wrote in message
...
On 2010-04-04, Michael Koblic wrote:

"Tom Ivar Helbekkmo" wrote in message
...

The problem came when I took the vise of the swivel base: The holes
were only 5/16" and I could not use my 3/8" T-nuts. In the end I cut
off some 3/8" bolts and turned a portion down to 5/16" and then cut
the appropriate size threads. Now the bottom goes into the T-nuts and
the top through the holes in the base and I do not take up additional
space through having to use the clamps.

That's clever! You can still use the swivel base if you need to, since
you haven't modified the vise in any way. How did you hold the bolts
when turning them down and threading them, without damaging the existing
thread?

I did it in my Taig which has a 3-jaw with aluminium jaws. I tried with
two
hex nuts etc. but in the end I just gripped them and ripped them. The
advantage - no damage to the threads. The PITA - the alu jaws do not grip
well enough to allow threading. On anything.

Hmm ... turn a ring for the OD of the aluminum jaws (or for
steps which you have turned on them to make them look like standard
chuck jaws) and expand the jaws into it to leave a grip diameter just a
little larger than as small as you can. Then drill the jaws (expanded
into the ring) to the tap drill size and start a tap into this on the
lathe with the rear end held in line by the tailstock center. Once the
tap is started, remove the chuck from the lathe and grip it in a vise
and finish tapping the jaws as deep as is reasonable for holding your
threaded stock. Then you can loosen the chuck (after removing the ring)
and easily thread the screw stock into it and clamp down on the thread
having much more grip surface.

Yikes! A bit of an overkill for just two bolts.

Or -- if you don't have soft jaws, take some aluminum of say 1"
OD (assuming your thread size is 1/2" or less), center drill it and
drill to tap size on the lathe while holding it in the 3-jaw chuck and
tap as before. Then remove from the chuck, and put a slitting saw in
your mill and cut a radial slit from the OD to the center hole. Now,
put it back in the lathe chuck, orient the slit directly opposite one of
the jaws, screw in your screw while it is loose, then tighten the chuck
to close the slit and grip the thread.

I can see that one. Presumably steel jaws will grip into the aluminum
outside and prevent rotation. I found that *anything* held in the aluminum
jaws was not held strongly enough for cutting outside threads. Perhaps it is
a function of the chuck tightening mechanism, too (two tommy bars rather
than a key). With smaller stuff (my gnomons) I got around it by using the
1/8" collet. But forgret anything over 1/4".

--
Michael Koblic,
Campbell River, BC