"Leo Plas" wrote in message
ups.com...
I am prospecting around for a used collet chuck for my lathe which has
a L-0 spindle. It appears that there are at least two types available
which I could use that seem readily available: Sjogren-Hardinge and
Jacobs rubberflex. I have only used Sjogren ones previously. Are
there reasons to favor one type over the other? I know that the
rubberflex collets have a greater range of adjustment and so fewer
collets are needed to cover the range of the chuck's capacity. Is the
accuracy of the two types significantly different? Do the metal jaws
of the rubberflex chucks hold workpiece better or worse than the solid
metal collets? Do they leave bite marks? I would appreciate any
comments or suggestions about these things. I would be using the chuck
mostly for personal projects. I don't know whether a good 3-jaw chuck
is just as accurate as a good condition collet chuck.
Leo Plas

Another option is the Pratt-Burnerd collet chuck, which came in lever-type
(production) and keyed type, which closed like a drill chuck. The P-B chuck
was similar to the Jacobs in that each collet had a range of 1/8", +/-
0.020, I think, but the collets were all metal. I'm pretty sure that both
Jacobs and P-B spec'd the runout at 0.0005" or less. Both Jacobs and P-B
sold their chucks for a variety of spindle configurations, including L-0.
The Jacobs chucks seem to come up more often on Ebay than the P-B types but
I don't think that the Rubberflex collets for these chucks are made anymore.
The P-B collets were still listed in MSC as of a year ago or so at around
$200 each.

Both types suffer from one disadvantage - they don't like stock that is much
shorter than the collet jaw length. Jacobs dealt with this by including
rubber plugs that could be inserted in the rear of the collets, but I don't
think that P-B had anything similar.

There were also at least styles of collet for each brand so make sure you
get a match if you the chuck and collets separately.

I've got both Jacobs and P-B chucks and prefer the P-B, though there really
isn't much difference in my (hobyist) experience The Jacobs is a little
more convenient to open/close since that only requires popping the lock ring
and rotating the handwheel whereas the P-B requires the use of a chuck key.
For frequent, long-term use the lever-type P-B chuck would probably make the
mosty sense.

Mike.