In article ,
Jack Erbes wrote:
On Fri, 08 Aug 2003 10:48:28 GMT, "ATP"
wrote:

Are double angle collets any better? I'm getting a set of DA400 that I plan
on using with my Nichols Miller so I don't have to disassemble the drawbar
to change endmill sizes.

In theory, the double angle collets are not pulled towards the spindle
as they tighten so the cutter extension or offset does not change.

Hmm ... I could see this with a single-angle, with a shoulder at
the back, and the nosepiece closing it at the front only. (I guess that
you could consider this double-angle, with the rear angle being 90
degrees. :-)

With a double-angle, with identical angles at front and back, I
would expect the collet to move in half the distance of the nosepiece
travel (once compression starts). In other words -- reduced travel, but
not zero.

For ones like the ER, which have a shallow angle at the back,
and a steep angle at the nose, I would expect the collet to move in
excess of that half of nosepiece travel.

I think that the shallower the rear angle, the better the
possible concentricity.

Also the collets in many of the double angle collets (like the ER
series) have a much larger gripping range. Those typically have a 1
mm or .040" range while collets like R8 and 5C only have a few
thousandths.

Agreed -- "ER" stands for "Extended Range" after all. I've got
a set of those for my Compact-5/CNC (which also fit the C5 milling head,
although that is actually mounted on a separate X-Y base, instead of to
the back of the lathe bed as was originally intended when it was
designed. :-)

I can certainly testify to the pull-in in the ER series of
collets used as either workholding or toolholding collets.

Enjoy,
DoN.

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