My Crawford list says that 5c are 20 degrees and 3c are 12 degrees,
please remember that as they close onto the work the angle will alter
so matching holes my be a slightly different angle to ensure that the
collet is located on the largest diameter.
On Sun, 4 Jan 2009 10:57:34 -0800 (PST), firstname.lastname@example.org
Thank you for that. I assume that you mean 24 degrees INCLUDED angle
for the 3C collets?
I cannot relate to the tapered bore being at a different angle to the
collet. IMHO If the collet is gripping a parallel part then to give
consistant grip over the length, the external collet angle and
internal bore angle must be equal. The flex over the length of the
collet sections should accomodate the diametral change.
I have seen a number of references that agree with Peter's implication
that collets bend inwards in a curve rather than moving inwards in a
parallel manner. Which is why it's highly desirable to use the correct
collet for the work. Putting what amounts to an 'S' bend into the
'fingers'? of a collet will take a much greater moment than simply
bending them in a little.
Whilst possibly frustrating from a definitive point of view, 0.0334
deg over the tapered land of a collet is 0.0003" approx. (three
tenths.) Why worry? It's going to close more than that.
On Mon, 05 Jan 2009 07:17:38 +0000, Richard Edwards
Yes the problem is this, the collet is locating on the taper and as it
closes (and moves into the cone on the machine), the point of contact
on the collet changes (assuming the two tapers are the same at the
start) and if we imagine the ultimate in a 5c where it is closing
about .010" undersize the point of contact will move down the collet
taper towards the centre.
The angle for the 3c is per side.
I agree that this is all rather acedemic and we al have better things
to do with our lives!
I would suggest that the closing force to give a parallel grip (the S bend)
would probably be about twice that required for a non-parallel
The only reasonable way to prove which is happening would be to blue a collet,
then grip some under sized stock in it. I would suspect that with a decent
collet closer, the parallel grip would be obtained at least for 10 thou
undersized stock. One day, I might get bored enough to investigate.
Granted that it is a very small amount, but if I quoted a Morse Taper
angle incorrectly I am sure it would be picked up and chastised.
Having seen the 20.0334 degrees quoted I would prefer some definite
confirmation or denial.
Machinery Handbook does not give info for 5C or 3C unfortunately.
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