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Thread sizes for eyepiece thumbscrews?

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8 replies to this topic

#1 Senex Bibax

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Posted 14 July 2019 - 09:12 AM

Did Japanese manufacturers from the 1960s and 1970s follow any specific standards for the thread sizes of components such as eyepiece thumbscrews? I have been trying to match the thumbscrew threads on a 1960s Tasco diagonal  with no luck. 3 mm is too small and 3.5 is too big. Standard North American machine screw threads have been no match either so far. I haven't tried small SAE threads yet, or (God forbid) Whitworth. I suspect they are an oddball metric thread but I haven't fund a match yet.

 

It is frustratingly like working on old Italian 2-wheelers. M7 studs?? Who the **** uses (or sells) M7 hardware? And then there are the little brass screws in the electrical terminal blocks. M2.5 - too small. M3 - too big.

 

Standards rule.



#2 starman876

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Posted 14 July 2019 - 09:50 AM

I think it all depended on how the lathe was set up.   However, I have found that a lot of the thread sizes used back then are no longer used.   Just like everything else things get changed and someone decides that the new design works better or everyone starts using a new standard. 


Edited by starman876, 14 July 2019 - 09:50 AM.


#3 clamchip

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Posted 14 July 2019 - 09:53 AM

Sometimes you run into the Japanese Optical Thread?, Japanese Instrument Thread?, I can never

seem to remember what its called.

But anyway it was popular, especially on Astro Optical scopes who made our classic Tasco models.

I usually take my part to the hardware store and try and find a match.

Ace hardware has a particularly good fastener dept.

If no match I will usually go with nylon screws, nuts, etc. or aluminum. These soft materials with a

little oil the thread pitch can be 'reformed' especially the nylon.

 

Robert



#4 apfever

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Posted 14 July 2019 - 10:04 AM

Back in 1948 there was a world wide meeting to consolidate various standards. This was a result of WWII ending and a need to 'universalize' way too many specifications on way too many things from different countries - Japan in particular.   One of the thread sizes popular then is what's called the Japanese Industrial Standard (JIS threads).  Many of the JIS threads were slated and now obsolete. Sometimes it seems that all the back stock of those threads ended up getting used on telescopes. 

 

The set screws to hold eyepieces vary a bunch. Not just from back then, but even today. There is no standard size. One of the more common sizes is the archaic JIS  M4X0.75, which is no longer made. The modern size is now M4X0.7  and that extra 0.05 pitch won't let them interchange. 

 

Good luck. 



#5 starman876

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Posted 14 July 2019 - 12:44 PM

Back in 1948 there was a world wide meeting to consolidate various standards. This was a result of WWII ending and a need to 'universalize' way too many specifications on way too many things from different countries - Japan in particular.   One of the thread sizes popular then is what's called the Japanese Industrial Standard (JIS threads).  Many of the JIS threads were slated and now obsolete. Sometimes it seems that all the back stock of those threads ended up getting used on telescopes. 

 

The set screws to hold eyepieces vary a bunch. Not just from back then, but even today. There is no standard size. One of the more common sizes is the archaic JIS  M4X0.75, which is no longer made. The modern size is now M4X0.7  and that extra 0.05 pitch won't let them interchange. 

 

Good luck. 

Is is amazing how little the difference needs to be so they will not interchange.  



#6 NinePlanets

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Posted 14 July 2019 - 02:11 PM

Oh, for heaven's sake people! Just run a standard tap through the bloomin' hole and be done with the silly oddball screws. Just use something normal. 4-40 is close to the little Jap thingys and more often than not you won't even need to drill first.

 

When I make focusers and accessories I typically go bigger and use 6-32 simply because it's easier to use with gloves, et al.


  • Chris Johnson, terraclarke and TSSClay like this

#7 ccwemyss

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Posted 14 July 2019 - 04:40 PM

If I'm going to re-thread, I usually start from the thread of what I can find for a replacement knob. Agena has these nice M4-0.7 screws, for example, that pass as close to original (and fit at least some diagonals). 

 

https://agenaastro.c...crew-short.html

 

Sometimes I can find things at local hardware stores, but it's hit-or-miss, since it's not a common item.

 

Metric taps and dies, however, are also scarce. The local Home Depot has none. Lowes has a small set. The nearest True-Value has none, but the one in the next town has about four common sizes. And the guys at Harbor Freight looked like they thought I was some kind of weirdo for even asking. 

 

Chip W. 



#8 Senex Bibax

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Posted 14 July 2019 - 08:20 PM

I have a very good local fastener supplier with a wide selection of metric and Imperial, even in stainless steel and brass. Nothing that matched the eyepiece screws, though. I have a set of taps and dies, and being in Canada I have both metric and imperial. I'll see what the smallest tap is that will enlarge the eyepiece threads to something standard.



#9 apfever

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Posted 14 July 2019 - 09:00 PM

I suggest a tap that is large enough to cut new threads, and not just cross thread through the existing ones.  You will have a sloppy fit if the hole is short with little threading and you only alter existing threads.

I also suggest going to a fine thread so you can get more turns in the metal. 




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