On 2011-09-07, Wes wrote:
Anyone have good pointers to where I can get a 6" scroll chuck with an adjustable back
plate? I know Buck makes one, I'm not sure what chuck we have on the LeBlond at work but
it is sweet being able to dial in concentricity. I'm trying to find the best deal on a
good chuck.

What spindle mount?

If you are after *new*, look at Bison chucks. Nice quality for
reasonable prices.

If you already have a good 3-jaw chuck with a separate
backplate, it is possible to adapt it to make one with an adjust-tru
style feature.

1) In preparation -- turn a chuck of steel to the OD of the chuck
and backplate, and then bore it to leave perhaps a 1" thick
wall.

2) Remove the chuck from the backplate, and drill and counterbore
the ring from (1) above to accept screws into the back of the
chuck to mount the ring firmly to it. You may want to set up
dowel pins so the ring can't shift relative to the chuck body.

3) Drill and tap the ring to accept screws through the backplate
holes a bit oversized into the ring. If you use the dowel pins
mentioned in (2) above, probably you should drill and tap these
holes all the way through the ring so you can use longer screws
as jackscrews to separate the ring and chuck body in the future
at need.

4) Bore a pocket in the backplate perhaps 1" smaller in diameter
than the ID of the ring.

5) Turn a plug of steel to be a snug fit into the pocket and to
project perhaps 3/4" or so into the ring -- maybe a full 1" if
there is sufficient clearance in the back of the chuck body.
Drill and counterbore it, and drill and tap the backplate for
screws to secure the plug rigidly to the backplate.

6) Drill and tap four radial holes for heavy setscrews at 90
degree intervals around the ring.

7) Grind the ends of the setscrews flat.

8) Assemble the whole thing, with the setscrews loose, and the
screws attaching the backplate to the ring sort of tight, enough
to keep the chuck from slipping down to whatever side is down at
the moment.

-------------------------------------------------------------------------------

9) Chuck up a piece of stock the diameter of what you are going to
work with at the moment.

10) Tap the chuck so it is moderately close, and then lightly adjust
the setscrews to touch the plug of steel.

11) Now, using the setscrews and with a runout indicator, adjust
for minimum runout as you would with a normal adjust-tru style
chuck.

12) Tighten the screws securing the backplate to the ring and
recheck the runout, as it may shift a bit with the tightening.


When you shift to a different diameter workpiece, slack the
backplate screws and go back to (9) above, skipping (10) except
for the first setup. (This is why the dividing line, to
separate the *making* from the *using* part. :-)

Good Luck,
DoN.

--
Remove oil spill source from e-mail
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 ---