10 replies to this topic

[Tala]

Hello,

 

I'm trying to find mechanical specs for astronomy thread with are not part of the official ISO tables; Such as Major, Minor and Pitch Diameters and class 

In particular M54 x 0.75 , M48 and M42, the M54 is the most important one. 

 

Does anyone know where can I get this information ? Couldn't find it anywhere.  

 

Thank you. 

 

[lmclouth]

This is a really good article about the different thread sizes and other info. 

https://agenaastro.c...-explained.html

 

Hopefully it helps.

 

One thread problem I've ran into was from SvBONY.  They said (and still say) their helical focuser is M36x1.0 threads when in fact they are M36.4x1.0 (as used by some Vixen/Takahashi products).  And they will NOT admit that they are wrong.

I had an adapter made based on their info (i.e. M36x1.0) and of course it doesn't thread on.  Fortunately the adapter maker knew that it must be M36.4 and sent me one made to those threads and it works great.

 

So good luck if you have to deal with them or another manufacturer who doesn't know their own products.  Luckily another SvBONY product I have does have the correct threads; so not all of their stuff has wrong information.

 

Lamar

Edited by lmclouth, 21 January 2021 - 06:21 AM.

[don clement]

There ain't no ISO or ANSI standards for commonly used threads on telescopes. I always have to give extra clearance when cutting telescope threads and if possible get a sample and thread to fit.  The exception to optics  thread standards is the RMS (Royal Microscopical Society objective thread) threads specifications can be found in the in the Machinery Handbook as AMO threads. And then RMS threads are whitworth thread form and are only 0.800" diameter. https://www.sizes.co.../RMS_thread.htm

 

Don

[steveastrouk]

Nothing like going to the source:

 

The Society had two plug and ring gauges, one 0.8 in. and the other 0.7626 in., made by Whitworth as standards for the use of the Society,

[don clement]

Here is an A.M.O. tap I have.

 

Don

 

[BGRE]

If only taps were available for the Mitutoyo microscope objective thread (same pitch Whitworth thread on a larger diameter).

At least Mitutoyo provide complete specifications for the thread.

[steveastrouk]

If only taps were available for the Mitutoyo microscope objective thread (same pitch Whitworth thread on a larger diameter).

At least Mitutoyo provide complete specifications for the thread.

Getting taps custom made is not prohibitively expensive, for small runs.

[skywolf856]

Here are calculations to establish minor thread diameter.

 

https://www.actx.edu.../filecabinet/15

[don clement]

If only taps were available for the Mitutoyo microscope objective thread (same pitch Whitworth thread on a larger diameter).

At least Mitutoyo provide complete specifications for the thread.

That is the problem with proprietary thread sizes that one just can't substitute one manufacturer for another as one would would do if Mitutoyo  had used standard RMS threads. I have a variety of microscope objectives from many countries and manufacturers that are all RMS threads and are all interchangeable. A good example is the  rear boss on some SCTs from Celestron and Meade. Meade chose a size listed in the Machinery's Handbook from the 16UN table as 3-1/4-16UN whereas Celestron used a non-standard size 0.05" less diameter. As a result one cannot interchange Meade and Celestron SCT adapters.

 

Don

 

Page from my 16th edition Machinery's Handbook

 

[BGRE]

RMS thread diameter is too small to suit the long working distance and NA of the Mitutoyo infinity corrected microscope objectives, Consequently a larger diameter thread is required. Why they chose 36tpi Whitworth threads on a nominal 26mm diameter is unknown (it may have been as mundane as already having the tooling to machine 36tpi Whitworth threads). Such microscope objectives can be useful in some spherical wave Twyman-Green, Fizeau or Haidinger interferometer variants.  

Edited by BGRE, 22 January 2021 - 09:36 PM.

[don clement]

RMS thread diameter is too small to suit the long working distance and NA of the Mitutoyo infinity corrected microscope objectives, Consequently a larger diameter thread is required. Why they chose 36tpi Whitworth threads on a nominal 26mm diameter is unknown (it may have been as mundane as already having the tooling to machine 36tpi Whitworth threads). Such microscope objectives can be useful in some spherical wave Twyman-Green, Fizeau or Haidinger interferometer variants.  

 Mitutoyo would be tooled for ISO metric and not bothered with outmoded Whitworth that isn't 0.8". Must have been a proprietary move.

 

Don