Subject: Re: Really Weird Thread time...

From: [email-masked] (James Kirkpatrick)
Date: 23 Nov 94 10:18:56 MST

[Tim's friend has a weird clock screw]

I don't have an answer, but you might try posting this to alt.horology
if your news system carries it.  Also there's a CLOCKS mailing list on
Bitnet; some details are in the FAQ, part 1 I believe.

If you do find an answer, I hope you will post the results!

Jim

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From: [email-masked] (Tim Kirby)
Date: 22 Nov 94 15:07:16 CST

Hi guys...

	I have a colleague here who is into the fine art of horology.
He came to me with a clock believed made in the UK sometime this century
that is missing a screw. He tried to gauge the thread pitch on another
screw in the clock and thought it to be 3BA; bought a tap & die, made a
new screw and... you guessed it - it doesn't quite fit.

I looked at it with the thread gauges and, sho 'nuff, it appears to be
33TPI. I couldn't find an Imperial, American or even Metric thread that
would suit.

The size is fractionally *larger* than 3BA (the 3BA screw is a sloppy fit;
the threads engage enough to bind after about 3 or four turns)

I've been through all my books and I can't find a thread definition that
matches it. Seemed like a good time to throw this one out for contemplation.

Ideas, anyone?

Thanks

Tim (Baffled)
--
Tim Kirby _________ Cray Research Inc., Eagan, MN, USA __________ [email-masked]
Software Division              System Support                +1-(612)-683-5390
__________________________ Consider it disclaimed ____________________________
If all else fails, Immortality may always be assured by spectacular error(JKG)

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From: [email-masked] (Peter Wiley - Poultry)
Date: 24 Nov 1994 22:46:50 GMT

33 tpi *is* a weird thread. But possible with a back-geared lathe, I think.
On my small lathe, 8 tpi leadscrew, a 16 tooth gear and a 66 tooth gear will
give 33 tpi.

I'd recheck the measurement. 32 tpi is *much* more common, given that small
lathes typically have 8 tpi leadscrews and a 32 tpi thread can be cut very
easily by re-engaging the split nuts anywhere on an 8 tpi screw.

Peter Wiley

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From: [email-masked] (Tim Kirby)
Date: 28 Nov 94 23:04:17 CST

Peter Wiley - Poultry ([email-masked]) wrote:
: 33 tpi *is* a weird thread. But possible with a back-geared lathe, I think.
: On my small lathe, 8 tpi leadscrew, a 16 tooth gear and a 66 tooth gear will
: give 33 tpi.

: I'd recheck the measurement...

Trust me, I rechecked it until I was blue in the face; I went through every
reference book I could find; no matter how hard I tried I could not make it
32 or 34 TPI, nor could I find an appropriate "prototype" thread...

Rest assured, if there is ever a conclusion I'll post it :)

Tim

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From: [email-masked] (Sergio)
Date: 29 Nov 1994 16:59:40 GMT

I am posting this article for a friend, Antonio Palama' who does 
not have Usenet access (e-mail answers to be sent to him directly: 
[email-masked]).

It easier to do it with 4 wheels, i.e. (20/45)*(30/55), BTW if you are
lucky enough NOT to have a Norton gear box on your lathe, you can cut any
thread with sufficient accuracy: example for 8 tpi leadscrew:
TPI         WHEELS
27          (20/45)*(40/60)
29.09       (30/75)*(55/80)
31.02       (25/70)*(65/90)
35          (20/50)*(40/70).

Ciao, Antonio.

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From: [email-masked] (Peter Wiley - Poultry)
Date: 1 Dec 1994 08:31:23 GMT

Oh, I believe you about the thread; there are a lot of perverse people out 
there who build things like this :)

I needed to make a replacement spur gear once for a lathe. It was 67 teeth.
Try cutting that without a differential dividing head and a lot of setup 
aggravation.

I made the replacement 66 teeth and upped the tooth count in its mate by one.
But why 67 teeth? It turns out that this is 4.928" OD for 14 DP so a clean up
cut on 5" stock is perfect. Still....

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From: [email-masked] (Tim Kirby)
Date: 3 Dec 94 16:35:23 CST

Bruce Holder ([email-masked]) wrote:
: Tim Kirby ([email-masked]) wrote:
: : Trust me, I rechecked it until I was blue in the face; I went through every
: : reference book I could find; no matter how hard I tried I could not make it
: : 32 or 34 TPI, nor could I find an appropriate "prototype" thread...

:   What's the chance that this is a metric thread?  33 TPI equals .030303
: inch lead, while .75mm lead equals .029527 inch lead, a difference of only
: .000776 inches per thread.

Uh, it didn't fit any metric thread gauges either. I suppose it is feasible
but a "not very new clock made in England" would be relatively unlikely to
have a metric thread...

Still looking :(

Tim

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From: [email-masked] (Bruce Holder)
Date: Thu, 1 Dec 1994 16:59:07 GMT

Tim Kirby ([email-masked]) wrote:
: Trust me, I rechecked it until I was blue in the face; I went through every
: reference book I could find; no matter how hard I tried I could not make it
: 32 or 34 TPI, nor could I find an appropriate "prototype" thread...

  What's the chance that this is a metric thread?  33 TPI equals .030303
inch lead, while .75mm lead equals .029527 inch lead, a difference of only
.000776 inches per thread.
--
Bruce Holder		[email-masked]
			(303)530-8739

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From: [email-masked] (Erik Halberstadt)
Date: 26 Dec 1994 14:06:00 -0800

Jeff Sweeney ([email-masked]) wrote:
: Tim Kirby writes:
: >Still looking :(

: Stop looking.

: What makes you think this thread must have a 'prototype'? Maybe it is
: one-off. Maybe the clock maker was having a bad day. Maybe she was
: playing a joke. Maybe it was the maker's way of assuring that nobody
: but herself would work on this clock...

: -- 
: Jeff
: [email-masked]

Well, in the absense of the original, I can only guess that the question 
at hand is one of screw threads in an older clock. Having some experience 
with these, and having read a bit on the subject, I may be able to help 
with this little tidbit: 

Clockmakers were known to cut threads by eye! It is possible that you 
have found a piece that was made by someone who made his own tooling, and 
are now faced with the dilema of having to do so yourself or modify a 
movement to make it functional.

Good luck!

Erik