I am trying to finish up some unfinished business with my Clausing
6913 lathe. This is my question #2. I have a three jaw chuck on it,
and while the outside of the chuck is relatively true (as seen with a
dial indicator), the parts held in the chuck run anything but
true. From previous discussions and my searches, I could try to
regrind or re-cut the jaws, right? And if so, which way is better? Can
I do it with a carbide insert and auto feed?
How much runout ?
Check the rounout at various diameters, 1" 2" 3" etc. If the runout is the
same ammount at any diameter just regrind the jaws. Use a ring so the
jaws are under load while truing. If the runout varies at different
the chuck is worn out and needs new jaws and scrol. Usualy its cheaper
to just buy a new chuck than try to fix one thats worn out. My 40 year old
bison 3 jaw has .002 runout. A carbide insert with auto feed will not work
very well in an interupted cut like a 3 jaw chuck.
Wrong question. What you should be asking is "where can I find a Buck
Adjust-Tru chuck to fit my lathe" (or Benard etc etc)
You might try new jaws..but most lathes will be lucky to give you
.003-.005 true with an already turned piece of rework in a 3 jaw.
Or 5c or 16C collets...which would be my suggestion given your ability
to score collets
You put a toolpost grinder, die grinder, Dremel or whatever you
have on the toolpost. You can use rings and pins or putty or
rubber bands to pull the jaws outward against the scroll, just
as it would be when gripping a part. Then you use the carriage
to run the grinder in and out across the jaws. I usually do this
a few passes with the carriage handwheel, then start the lathe
running and make a few passes with the power feed. You then
disassemble the chuck to remove the grit that has sprayed all
over the insides. Protect the lathe bed with wet towels (the
water helps trap the flying grit.) We paper towels on cardboard
work well, too.
This fixes bell-mouthing, ie. excessive wear at the tips of the
jaws. The bell-mouthing allows work to wobble in the jaws
while turning, and you get out-of-round work, generally with 3 lobes.
If the scroll is damaged or not constrained to center by the chuck
body, regrinding the jaws will not help. You may be able to
insert a rolled brass shim to constrain the scroll to the
I suppose you can do it with a carbide inset, but I've always
This is an interesting thread, 'cuz I learned from someplace (which I
cannot now remember!) that you just don't trust 3-jaw chucks to not have
runout -- if you want precision without runout you use a collet set, or
you use a 4-jaw chuck and spend the time to dial it in each time you
mount the piece.
By "run true" do you mean that a round piece has runout, or that it's
Years ago an apprentice was taught that a three jawed chuck was never
expected to hold a work piece exactly "true" and one always started
with a slightly oversized piece of stock and when the O.D. was turned
to size it was, of course, "true".
The standard rule was that one never removed the work piece from the
chuck until it was finished. One could however, usually remove the
entire chuck with work piece from the lathe and reinstall it without
Are the Jaws in the correct slots ?
Is the chuck screwed on ? or is it a snap fit ? Is it clean and not
pushing it aside ?
When I got my Dad's lathe, he had shipped it and just put on the chuck
for rough work on something - never leveled it or such. I then was
called and told to come and get it - Mom and Dad moved in with Sister
and the Lathe was in the Laundry room... I come home with it and
found a chip in the threads that shifted the chuck off center.
The swirl inside had a number of chips - I cleaned and greased.
Put the chuck back on and it ran true.
Cleaned the 4-jaw just for general purposes.
Might be a chip issue.
20 years ago I trued the jaws in my 3-jaw chuck for my Reed-Prentice. I
closed the chuck on a spider behind the jaws and used an air die grinder
with a 2" long x 1" diameter stone mounted on the tool post. I took
tiny-tiny cuts. The jaws are square and hold .002" easily. And, I
haven't had to do it again. Also, I always do the final tightening on
one key hole that happens to be the one CCW from the label. One hole
will ALWAYS be the "ONE" on any chuck.
Ah, that might be different! What chuck mount is this?
If D1, then there may be dirt between the spindle face and the
chuck backplate, or between the backplate and chuck body, if
built that way. After checking the interface between spindle
and backplate, if the chuck can be separated from a backplate,
just face off the chuck side of the backplate and then re-mount
the chuck. Do the same with any mount where the chuck can be
taken off the backplate. Face it until it turns the entire
area. This provides a mounting plane that is entirely perpendicular
to the spindle axis. Any good chuck should then mount precisely
to that plane. Do all this before any grinding operation.
Any time a chuck is moved from one machine to another, you want
to check for wobble (technically nutation) and face the mounting
surface if required.
Jaws should not be turned---they should be ground, as they are usually quite
hard, and won't turn uniformly as a result.
If you are not familiar with the prescribed procedure for preparing soft
jaws, I'd suggest you do nothing until you are. In order for the end
result to be useful, there are things you should do to ensure the proper
results. One of them is to use a dedicated socket, as each one tightens the
scroll differently, resulting in more or less run-out of the jaws. One's
choice should be the one which yields better results, so it should be used
in all cases, including tightening the jaws on the spider before grinding.
This socket should be well marked, so it is the only one used.
If you have two piece jaws, I'd suggest you explore the use of soft jaws
instead of screwing around with the hard jaws. They open the door to
solving all manner of chucking problems, and can be relied upon to repeat
within a half thou or less. If you're not familiar with soft jaws, I can
provide a link that will give you a serious amount of information, helping
you better understand how they are used. Please ask if you are interested.