In article ,
Ed wrote:
I'm considering purchasing a 5C collet chuck for my lathe. I'm
currently using 3 & 4 jaw chucks and want the added accuracy of 5C
collets.
You'll get better concentricity with a drawbar through the
spindle, if your late is big enough. To use a drawbar for 5C collets,
you need at least a 1-3/8" bore through the spindle. Then you need a
closer nosepiece to fit your internal spindle taper. Once you have
that, and good quality collets, your concentricity is limited by:
1) The exiting taper in the spindle.
2) The accuracy of the closer nosepiece (Royal makes some
very nice ones.)
3) The accuracy of the actual collet.
You will also probably prefer the lever style closer mechanism
(often found on turret lathes), instead of the handwheel on the outboard
end of the spindle.
If you don't have the 1-3/8" spindle bore, you will have to use
something like the Bison collet chuck, which while good quality, is not
as convenient for quick part changes. You'll be stuck with having to
use a key like that for the 3-jaw chuck to tighten and loosen the
collets -- and to change collets.
If concentricity is important, with the collet chuck, you really
should spend the extra for the "adjust-tru" feature, which lets you tune
the centering of the collet chuck after mounting it on the spindle.
Having no experience with 5C collets, can someone tell me if
they will hold my work: I work a lot with bar stock in the range of
0.7" to 1" diameter, in pre-cut lengths of 0.120" to 0.5". I need to
bore these pre-drilled pieces to ID's ranging from 0.5" to 0.8". This
is not production work - I can't build a specialized fixture or modify
a collet for each piece.
The length to diameter ratio makes things a bit more difficult,
especially with some less than 1/8" in length, and perhaps 1" in
diameter. You could (as others have suggested) make special stops which
are tubular section to clear the boring bar and hold the workpiece in
the collet.
Note -- that if these workpieces were not already cut to length,
you would be better to work with bar stock through the collet (you can
pass up to 1" bar through the spindle and the collet and drawbar). then
you turn to diameter (if necessary), drill and bore, and part off just
outside the collet, then you loosen the collet and advance the bar far
enough so you can produce the next piece. For this kind of operation,
the lever style closer is particularly nice. But -- you haven't yet
said whether the lathe is big enough to allow this.
I plan to have 5C collets in 1/64" sizes for my OD range. Will
standard 5C collets hold my work for boring? What I mean is, I don't
want to bore a step in the collets (I'm not doing production work) to
hold the piece a fixed depth in the collet. I'd like to have some
sort of internal collet stop that still allows the 3/8" boring bar to
pass through the center. Any help is appreciated.
Aside from making a special tubular depth stop as others have
suggested, which is still some special work for each size of stock you
want to work with since you can't buy them, the alternative (also
mentioned by some) is the collets designed to be bored to the size you
need -- and this could include a step to hold the depth, and keep the
thin workpiece square to the axis of the lathe. These are not of a
hardened steel (like normal collets), but rather a mild steel -- or even
brass -- with three pins to hold the pre-slit jaws opened to normal
spacing while you're boring to size for the workpiece (and boring
clearance behind the stop to accommodate the boring bar). Once you have
it to shape, you remove the pins, and the collet will close down on your
workpiece as you draw it in. Your diameter range is 0.700: through
1.000" -- but in what size steps? If just a few, it would be worth
while to bore several collets to size for each project. Alternatives
would be to bore a series of steps so the collet can hold more than one
size (size steps not too close together), and use a second one for the
intermediate sizes.
Note that to hold a collet nosepiece, the spindle taper will
probably need to be a MT-4 or larger. Mine (a 12x24" Clausing) is
MT 4-1/2. If you have the 1-3/8" spindle bore, you probably also have a
spindle taper large enough to accept the nosepiece. And if you have a
Hardinge lathe, it probably has a spindle designed to accept 5C collets
*without* an adaptor nosepiece.
A companion to the nosepiece is a spindle thread or taper
protector which is also used to remove the nosepiece. *Don't* put the
nosepiece in without the protector in place, or you may have to do
things which would damage the nosepiece or the spindle nose itself to
remove it.
Good Luck,
DoN.
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