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Odd thread

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Alan Charleston05/01/2021 05:40:22
105 forum posts
20 photos

Hi,

I bought an old Hilger and Watts refractometer on the local auction site. It has a 6" thermometer in a metal case sticking out the side, which was snapped off during delivery. The metal case is attached to the instrument via a ring of knurled brass with male threads on both sides. This is the thing which broke, and I need to make a new one. The thread is however odd. The OD is 8.5mm (.335" and it has 40TPI. At first I thought it might be a 5/16" model engineers thread, but the 40TPI only applies up to 1/4" and then it drops to 32TPI and 5/16" is only 7.9mm in any case. I have made a piece of threaded rod 8.5mmOD X 40TPI using a 60 degree cutter and it screws nicely into the thermometer case and the instrument. The threads only extend about 5mm from the knurled disc in the middle, and I'm not keen on cutting such a short thread up to a shoulder. I would rather use a length of threaded rod screwed through the disc and loctite it in place. To do this, I need a tap. Anybody got any suggestions as to what the thread is?

Thanks,

Alan

pgk pgk05/01/2021 06:26:59
2060 forum posts
290 photos

a)...cut the thread outbound from headstock from a shoulder...
b)...remove thread from part of your threaded rod and threadlock/press fit the disc.
c)...make a tap

pgk

Ian B.05/01/2021 07:05:38
163 forum posts
5 photos

Might be worth a talk to Tracey Tools. They are often able to help with off standard threads. I needed a tap for Ronson gas filler valves. They supplied. Then I had access to buy really cheap pencil gas soldering torches when the Ronson supply of valves dried up for a bit. Yep the gas filler valves were an even odder thread. Tracey were able to supply the taps I needed.

Ian

DiogenesII05/01/2021 07:09:51
197 forum posts
88 photos

doesn't 5/16 ME thread come as 40tpi..?

Tracy Tools 5/16 x40 ME

Edited By DiogenesII on 05/01/2021 07:13:00

Michael Gilligan05/01/2021 08:43:48
avatar
17318 forum posts
786 photos
Posted by DiogenesII on 05/01/2021 07:09:51:

doesn't 5/16 ME thread come as 40tpi..?

Tracy Tools 5/16 x40 ME

.

dont know

5/16” is not 8.5mm

MichaelG

DiogenesII05/01/2021 09:18:59
197 forum posts
88 photos

face 24 ..quite so..face 24

Martin Connelly05/01/2021 09:20:27
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1663 forum posts
179 photos

The Unified thread series includes constant pitch thread series but does not list 40tpi as one of them. Did you know that that all Swagelok Fittings use the same pitch regardless of the diameter? There is nothing to stop a designer from specifying a thread with 40tpi but not use 1/4" or 5/16". That is the difference between standard threads and non-standard threads. Just assume it is a non-standard thread and make one the same. It will require single point threading or the manufacture of suitable tooling.

This is not an odd thread, just an unusual or a non-standard one. Odd would be some outlandish number of threads per inch or an outlandish mm pitch. If you had 40⅞" tpi or 1.37633mm pitch that would be odd.

Martin C

Michael Gilligan05/01/2021 10:02:08
avatar
17318 forum posts
786 photos
Posted by Martin Connelly on 05/01/2021 09:20:27:

[…]

This is not an odd thread, just an unusual or a non-standard one. Odd would be ...

.

I think many dictionaries, and common usage, might contradict that assertion, Martin

MichaelG.

Martin Connelly05/01/2021 11:17:32
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1663 forum posts
179 photos

I can think of no way to describe 40tpi as an odd thread. In combination with an unexpected diameter it is an unusual and non-standard combination of thread and diameter. The forum thread title is "Odd thread" and this is not the case. Maybe we are both (OP and my first reply) being a bit lax in our description of thread as meaning a specific thread and diameter combination.

Martin C

JA05/01/2021 11:42:15
1100 forum posts
62 photos

A microscope thread? They were Whitworth form, used in brass and quite fine. I have cut a few, internal and external, on a lathe.

JA

Oily Rag05/01/2021 13:02:33
avatar
314 forum posts
126 photos

Could it be a 11/32" x 40tpi? 11/32" is 0.343" decimal which is what I would expect a 0.335" diameter across the crests would translate as. Instrument special?

Baz05/01/2021 14:19:06
524 forum posts
2 photos

11/32” x 40tpi gets my vote.

Michael Gilligan05/01/2021 16:46:19
avatar
17318 forum posts
786 photos
Posted by Martin Connelly on 05/01/2021 11:17:32:

I can think of no way to describe 40tpi as an odd thread. In combination with an unexpected diameter it is an unusual and non-standard combination of thread and diameter. The forum thread title is "Odd thread" and this is not the case. Maybe we are both (OP and my first reply) being a bit lax in our description of thread as meaning a specific thread and diameter combination.

Martin C

.

Sorry, Martin ; but I think ‘odd’ is a perfectly reasonable word to describe something which is ‘an unusual and non-standard combination’ ...

Let’s just agree to differ ... It’s a trivial point, not the substance of the question.

MichaelG.

Andy_G05/01/2021 16:59:51
111 forum posts
Posted by Alan Charleston on 05/01/2021 05:40:22:

Hi,

I bought an old Hilger and Watts refractometer

Any chance of a photo? I may have a (photocopy) of the manual for one if you are interested. (may be a completely different type though).

 

Edited By Andy_G on 05/01/2021 17:00:31

Alan Charleston06/01/2021 05:01:56
105 forum posts
20 photos

Hi,

Thanks for all the replies. I think I'll try option a or b as set out by pgk.

Thanks for the offer of a manual Andy but I found a pdf copy of one here:

https://physicsmuseum.uq.edu.au/abbe-refractometer

Regards,

Alan

Michael Gilligan06/01/2021 07:15:57
avatar
17318 forum posts
786 photos

That’s a great find, Alan

... Good to see that someone has gone to the trouble of scanning the document properly !

... There are far too many unusable copies of documents like this

MichaelG.

Andy_G06/01/2021 12:15:24
111 forum posts
Posted by Alan Charleston on 06/01/2021 05:01:56:

Hi,

Thanks for the offer of a manual Andy but I found a pdf copy of one here:

https://physicsmuseum.uq.edu.au/abbe-refractometer

Regards,

Alan

It would have been the wrong type, anyway - that's an Abbe refractometer, the one (I think) I have is for a Hilger-Chance - like this:

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