Runout on 3 Jaw Chuck

Well I took the 8" Buck Chuck apart and cleaned everything up. This is
not an adjust-tru chuck but is stamped with an S547. It came with my
'57 Sheldon Lathe so I am assuming it is original. I could not get the
scroll body out of the chuck body. It appears to be a heat fit.
Meaning it looks like the chuck body was heated until it expanded and
then the scroll body was put in. I could not get it out for anything.
I checked the runout on the spindle (.0005"), checked runout on
backplate (.0005"), and checked the body of the chuck and it was
around (.0005"). Chucked up a piece of cold roll steel and it had .01"
runout. That is either a problem with the stock or a problem with the
chuck jaws. I am going to get another piece of drill rod and try it
again. The backplate was such a tight fit into the chuck body that it
had to literally be pulled into the chuck using the outside allen head
screws and this was after being lubed with SAE30 machine oil. There is
no provision for adjusting the backplate while it is on the spindle
because the fit is so tight inside of the chuck it cannot be moved. I
don't believe moving the chuck around the backplate will make a
difference either. From what I can see of the scroll it looks like it
is in very good shape. The jaws also look very good and they are all
in their proper position. Any suggestions if the runout is still there
with the drill rod? What about shimming the backplate and chuck body
to offset the runout? Will this only be good at that diameter? Thanks,
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Opinions will vary, but .0005" runout on any part is about as good as it'll get for home shop machine parts, in my estimation.
You can find a procedure for truing up the jaw faces in the RCM archives, with a small grinder (Dremel or other type), and you'll be in good shape.
This will depend on the fit of the jaws to the chuck, and the position the jaws are in when you do the truing. If the jaws don't fit the chuck body tightly (with no material chucked), then a new set of jaws or other work will be required.
I haven't encountered a scroll mounting method that you've described, maybe some more investigation (or other owners) will reveal a way to disassembe it.
WB ................
Reply to
Wild Bill
I've got the same problem with my 4" 3 jaw (Crown) chuck, it runs true on the spindle but a precision ground 1" rod chucked in it runs out between .002" and .020". I dismantled the chuck; the scroll wouldn't budge at first, but I used a plastic drift through the jaw slots to knock it down ; you have to do this gently moving around the 3 slots as you go so as not to skew it as it is a precise fit in the body. Once I had the scroll out, I refitted the jaws and found that I had .0015" of lift in the no. 1 jaw which explained the poor repeatability. I don't know where to get spares for this chuck, so it's destined for the rubbish bin eventually. Martin.
Reply to
Martin Whybrow
What do you mean by "Lift"? Thanks, Steve
Reply to
Sorry, that's the best description I could come up with at the time. What I meant was play at 90 degrees to the chuck body face; imagine the chuck laying on a bench on its backplate, then the play meant the jaw could lift upwards. Martin.
Reply to
Martin Whybrow
If your jaws are worn on the surface facing the workpiece, check old listings by brownnsharp for an idea which will often help
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