On 2010-04-04, Michael Koblic wrote:
"DoN. Nichols" wrote in message
...
[ ... ]
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
[ ... ]
Yikes! A bit of an overkill for just two bolts.
Yes -- it makes more sense with more to do -- but consider
future use and mark the jaws in slot number order so you can re-use them
again at need. (Oh yes -- you can also turn the jaws around and use the
other end for a different special holder.
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.
How were you cutting the threads? Given that the lathe was a
Taig, I suspect that you were using a die. Single point cutting (in
multiple passes) the thread using a geared lathe feed generates a lot
less force, so you can cut threads without the workpiece slipping like
it was for you.
BTW Aluminum jaws gripping an aluminum "threaded collet" such as I
described above will grip better than smooth steel jaws on
aluminum -- though most steel jaws are not smooth. :-)
But if you bore a set of the aluminum jaws to a close fit on the
collet you just made, you will have better grip -- especially
considering that aluminum on aluminum tends to gall, improving
your grip. :-)
And -- you can take some valve grinding compound, and roll the
OD of the collet in that (with some force), so when the jaws are
tightened, the jaws grip a lot better by embedding the compound
in both the jaws and the OD of the collet.
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".
Longer Tommy bars will give more leverage. Make them of a
larger diameter steel, with the ends turned down to fit the holes and to
bottom with very little turned down diameter left extending. Perhaps
make them of drill rod, and harden and draw appropriately. You don't
want them too hard (brittle), but you want them harder than the supplied
state of the drill rod.
But be careful to not make them too long, or you will deform the
holes in the chuck body and the scroll plate. Consider that my Taig
3-jaw only has the holes in the scroll plate, and I need to grip by the
chuck jaws to keep it from turning. (Hmm ... I probably should drill
holes for the Tommy bars in the chuck body to go with those in the
scroll plate.)
But yes -- the chuck key is giving you a *lot* of leverage for
tightening the scroll plate.
BTW -- how well lubricated is the scroll plate? The less you
have to fight friction in the plate bearings and in the scroll to jaw
tooth engagement, the more of your force will go towards tightening the
chuck jaws on the workpiece.
Good Luck,
DoN.
--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. |
http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---