On 13 Oct 2003 11:56:37 -0700, (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. 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.

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.

Regards,
Ed Ferguson
Greetings Ed,
Collets will work in your application. Not only are adjustable stops
available but also spirin loaded stops. So these push the part out
when the collet is released. If the collet mounted stops won't work
because the part is too long then a stop which mounts in the spindle
tube or collet closer draw tube will work. If you are going to get
one of the closers that uses a key (like the Bison Brand) to close the
collet and the part is long then a stop that fits into the spindle
through hole will be the best option. Some are available in catalogs
but making one is simple. You can turn a piece of aluminum (or most
any metal you have lying about) to the size that fits your spindle
hole, at the rear, about .004" under, saw it in half at about 45
degrees, mill the sawn faces smooth, tap one of the halves and drill
the other. Then, screw a piece of all-thread through this piece so
that the end of the all-thread is where you want the part to bear with
the wedge shaped piece at the rear of the lathe. Slide the piece
without threads on the all-thread and use a nut to tighten the wedge
shaped pieces together. This will fix the stop in your lathe. On the
business end of the all thread you screw any shaped piece on you want
that will allow your tool to go completely through the part. An
advantage with this type of stop is that it is a "dead length" stop.
So as part diameter changes the part will always be stopped in the
same place. With a collet mounted stop as the diameter varies and the
clamping pressure varies the part length varies. This is because the
collet is drwan back into a taper to cause the collet to collapse
against the part being held. With a smaller part, or with higher
clamping pressure, the collet is drawn back farther into the taper.
There are closers that move the taper and the collet is stationary but
these are expensive. More convienient, but more expensive that the
Bison type closers that use a key are the lever actuated closers.
Cheers,
Eric R Snow,
E T Precision Machine