Weird Collet Thread

[Roderick JenkinsParticipant @roderickjenkins93242]

Schaublin W10 Collet

[Roderick JenkinsParticipant @roderickjenkins93242]

The draw bar thread on a Schaublin W10 Collet is 0.833mm buttress. Where has this pitch come from? W20 collets have a 1.693mm pitch which is 15tpi. One might suppose that W10 collets have a 30tpi thread but that is 0.847mm not 0.833mm (which is 30.5 tpi).

Any thoughts?

Rod

[JasonBModerator @jasonb]

maybe Mr Schaublin forgot he had a metric leadscrew when he cut the thread on the collets its 30 threads per 25mm

[Michael GilliganParticipant @michaelgilligan61133]

I’m sure I have a note about this somewhere, Rod

… off out now, but I will look for it this evening.

MichaelG.

[JasonBModerator @jasonb]

Michael, no real need to look as 25mm divided by 30 is 0.8333, it's just one of those odd metric/imperial combinations which answers where the pitch came from.

Bit like 20tpi on shanks of metric milling cutters

Edited By JasonB on 26/04/2022 14:38:16

[DC31kParticipant @dc31k]

That's the trouble with keeping those nasty decimal points in your head.

Think in terms of fractions and you see that 0.833 is 5/6 (of 1mm).

The W20 thread is more commonly expressed as 1.667, or in fractions, 5/3.

Change gears do not come in decimals. They come in integers. And the ratio of two integers is a fraction.

[Roderick JenkinsParticipant @roderickjenkins93242]

Posted by JasonB on 26/04/2022 14:37:17:

Michael, no real need to look as 25mm divided by 30 is 0.8333, it's just one of those odd metric/imperial combinations which answers where the pitch came from.

Bit like 20tpi on shanks of metric milling cutters

Edited By JasonB on 26/04/2022 14:38:16

But, as I understand it are 20 tpi, not some nearly but not quite metric equivalent.

Anyway, the responses suggest that Schaublin took the American Webster Whitcomb imperial pitches and converted them to the nearest convenient setting on a metric lathe. Seems reasonable but I wonder why they didn't choose 1mm like many of the other collet manufacturers.

[Peter Cook 6Participant @petercook6]

Posted by Roderick Jenkins on 26/04/2022 17:13:31:

I wonder why they didn't choose 1mm like many of the other collet manufacturers.

Proprietary lock in – non standard fittings make it hard to buy elsewhere. It's been around a long time.

[SillyOldDufferModerator @sillyoldduffer]

Posted by Roderick Jenkins on 26/04/2022 17:13:31:

Posted by JasonB on 26/04/2022 14:37:17:

Michael, no real need to look as 25mm divided by 30 is 0.8333, it's just one of those odd metric/imperial combinations which answers where the pitch came from.

Bit like 20tpi on shanks of metric milling cutters

…

…

Anyway, the responses suggest that Schaublin took the American Webster Whitcomb imperial pitches and converted them to the nearest convenient setting on a metric lathe. Seems reasonable but I wonder why they didn't choose 1mm like many of the other collet manufacturers.

My guess is it's a deliberate proprietary thread designed to protect a patent. The advantages of standardisation are obvious to us a century after Schaublin introduced his collets, but back then his needs were commercial. I suspect MT tapers are weird for the same reason: in court, a patent infringer can't claim to have chosen the same tapers for a rational reason.

Dave

[DC31kParticipant @dc31k]

A curiosity of the W-series collet threads is that W10 is 10/12 mm pitch. W15 is 15/12 mm pitch and W20 is 20/12 mm pitch.

Against that, W12 is also 5/4 mm pitch, W25 is a true 15 tpi, and W31.75 is a true 20tpi.

See catalogue extract in post 2 here:

https://www.homemodelenginemachinist.com/threads/w12-collet-threads.8436/

There is also a Schaublin product catalogue from 1946 on Scribd (stamped with Wickman Machine Tools) that shows their E-series collets, the precursor of ER collets.

[Michael GilliganParticipant @michaelgilligan61133]

Clearly there is no need for my input

DC31K has explained the logic exquisitely.

MichaelG.

[Roderick JenkinsParticipant @roderickjenkins93242]

Thanks guys, especially DC31K. I am much more comfortable now I can see some logic in the system. Everyday is a school day

Cheers,

Rod

[Michael GilliganParticipant @michaelgilligan61133]

This 263 page catalogue downloads very quickly: **LINK**

http://www.schaublin.ch/app/webroot/pdf/cat/5.pdf

It’s very informative, and will surely impart an appropriate pride of ownership.

MichaelG.

[DC31kParticipant @dc31k]

At the risk of over-egging the pudding, note that 10/12 pitch is 12 threads per centimetre; 15/12 is 8 threads per centimetre and 20/12 is 6 threads per centimetre. 1mm pitch is 10 threads per centimetre. Expressed in these terms, which are a close analogue of the way imperial threads are discussed, the pitches seem entirely reasonable and it is something like 1.5mm pitch that looks like an oddity.

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