# Hardinge collet angles

• posted on January 4, 2009, 5:48 pm

Gentlemen I need to determine the collet angle on 5C and 3C collets. I have seen the 5C quoted as 20 degrees inclusive and also 20.0334 degrees. Which is correct? Also what is the angle for a 3C? Thank you

Richard

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• posted on January 4, 2009, 6:57 pm

wrote:

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. Peter

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• posted on January 5, 2009, 7:17 am

On Sun, 4 Jan 2009 10:57:34 -0800 (PST), snipped-for-privacy@hotmail.com wrote:

Peter 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.

Richard

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• posted on January 5, 2009, 10:32 am

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.

Richard

On Mon, 05 Jan 2009 07:17:38 +0000, Richard Edwards

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• posted on January 5, 2009, 12:46 pm

wrote:

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! Peter

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• posted on January 5, 2009, 11:06 pm

On Mon, 05 Jan 2009 10:32:47 +0000, Richard Shute

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 gripping-at-one-end grip.

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.

Mark Rand RTFM

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• posted on January 6, 2009, 7:53 am

On Mon, 05 Jan 2009 10:32:47 +0000, Richard Shute

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.

Richard