On 2010-04-27, steamer wrote:
--I've got a 5" Buck 6-jaw on my Myford Super 7. Had to make a
backplate as none were available but worth every bit of heartache to get it
done. If Buck makes a chuck small enough to fit your lathe go for it. Nice
thing about the 6-jaw: you can leave one jaw out, if necessary, to
accomodate lumpy castings, etc but the full 6 gives you the ability to grip
relatively small stuff: 3-jaw chucks tend to have fairly blunt gripping ends
but the 6-jaw variety are much pointier, so to speak.

Also -- another significant advantage to a 6-jaw is that when
clamping thin-walled tubing the 6-jaw introduces less deflection than
the 3-jaw does.

However -- a benefit for the 3-jaw. With an irregular surface
on the workpiece, a 3-jaw *always* gets full contact with each jaw.
(3-points are self centering). With 6-jaw, it is likely that one or
more of the jaws will not be making proper contact, reducing it in
effect to a 3-jaw with skinnier points.

And for either 3 or 6 jaw -- if the chuck has a separate
backplate, it is possible to make a spacer with some other features to
turn it into an Adjust-Tru (or any of a number of other trademarked
names, depending on the maker of the chuck. :-)

First -- you turn a recess in the center of the mounting plate,
and mount a round piece of steel in that, with several countersunk
bolts. Best if it is a good tight fit in the recess so it can't shift
in there.

Then -- turn up a spacer ring to go between the chuck body and
the backplate. Drill and countersink it for bolts to attach it to the
chuck body which go into the threaded holes which the backplate normally
bolts to.

Drill and tap four radial holes at 90 degree intervals around
the ring for setscrews to press on the original round piece of steel.

Then drill and tap holes in the ring to match the holes in the
backplate, enlarge the backplate holes (and countersinks if present) a
bit to allow motion, and attach the ring to the backplate with these.

In use -- loosen the backplate bolts to finger tight, and use
the radial setscrews to shift the chuck to true (relative to the
backplate) for the workpiece size in use at the moment, and snug the
backplate bolts and re-check the centering. If it is still on center,
snug them down firmly and triple check the centering. You are now ready
to turn.

Enjoy,
DoN.

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