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help please - metric / optics equipment threads

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#1 john gabriel

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Posted 20 January 2014 - 10:14 AM

Are "T" and "T2" threads just shorthand for M42 x .075 and M48 x 0.75? Please correct me.

I recently bought this focuser with M46 x 0.75 male thread. The M46 thread size seems almost non-existent in the literature and is not found in metric thread tables. I wonder if this a seller's typo, or did I buy a sub-standard product now being shipped all the way from China that won't fit into anything.

The problem is I've found at lease two (possibly 3) very similar focusers listed as M46 for guide scopes.

Would an M46 x .75 male thread into an M48 x 0.75 female? Is the M48 also called "T2"?

My humble thanks to anyone who can straighten me out on these confusions.
John

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#2 Madratter

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Posted 20 January 2014 - 12:05 PM

Bumping this for you.

This should help.

http://en.wikipedia.org/wiki/T-mount

T2 is not M48. That is the threading used for 2" filters.

#3 john gabriel

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Posted 20 January 2014 - 02:32 PM


T2 is not M48. That is the threading used for 2" filters.


Meaning that both T and T2 are M42? I found the wiki article confusing. :p

I'm wondering if the focusers from China are either defective major thread dia. or if their sellers have just gotten into a repeated typo? There appears to be no such thing as an M46 in any of the metric tables I've looked at.

#4 Madratter

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Posted 20 January 2014 - 02:42 PM

Strictly speaking, as the article indicates, not all T adapters are necessarily T2 and not all are necessarily M42. In terms of modern T adapters, my guess is that almost all are T2. But I'm not sure about that.

As for M46, I haven't heard of it, but I'm more inclined than not to think it is NOT a typo.

At any rate, I think you'll probably have better luck in the equipment forum with this question.

#5 john gabriel

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Posted 20 January 2014 - 03:07 PM

Thank you! I will probably just copy over the original question and then edit. (I guess I could ask the moderator to move the thread - dunno?)

Thanks again.
John

#6 john gabriel

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Posted 21 January 2014 - 03:30 PM

bump - no takers? Anyone heard of an M46 x .75 thread on any equipment?

#7 sternsplitter

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Posted 21 January 2014 - 03:36 PM

M46 is a standard thread. One barrel of my Meade #930 diagonal mirror screws with M46 into the body. That barrel is rather long (intended for using a Barlow lens). For attaching a camera and to get into focus I removed it and used an adapter Baader #2958046 instead which has a M46 thread (Google).

Regards, Martin

#8 Mark9473

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Posted 21 January 2014 - 03:52 PM

Meaning that both T and T2 are M42? I found the wiki article confusing.


T thread is M42x1.0 whereas T2 is M42x0.75 so the threading is different.

#9 MikeML

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Posted 21 January 2014 - 05:04 PM

T thread is M42x1.0 whereas T2 is M42x0.75 so the threading is different.


M42 x1 is a Pentax or Universal thread. T and T2 are both M42 x0.75

#10 john gabriel

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Posted 21 January 2014 - 05:08 PM

M46 is a standard thread. One barrel of my Meade #930 diagonal mirror screws with M46 into the body. That barrel is rather long (intended for using a Barlow lens). For attaching a camera and to get into focus I removed it and used an adapter Baader #2958046 instead which has a M46 thread (Google).

Hi Martin,
Thank you for replying! I'm sorry I'm not sure from your description which part(s) would have the female M46 thread - sounds like probably the diagonal body part, which means the Baader #2958046 has both male and female ends(?).

I'm looking for any reasonably priced accessory that has female M46 x 0.75 thread. In 3 days of googling and supplier inquiry I've not found that. Thank you!
John

#11 john gabriel

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Posted 21 January 2014 - 05:21 PM

Hi Martin,
Baader #2958046 only has the male M46 thread. Won't work. Now if I could only buy your diagonal body from you.... :D

John

#12 MikeML

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Posted 21 January 2014 - 06:01 PM

Looks like an Ebay special. It may thread directly into a 50mm finder tube. One caveat, not all 50mm tubes are the same diameter. You might try some of the photo stores for step up and step down adapters. As a last resort find a machine shop that can make an adapter $$$ unless you have a friend that can make it.
Good Luck, BTW, I'm curious as to how you make out with this.

#13 john gabriel

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Posted 21 January 2014 - 07:16 PM

Thank you Mike - you been very helpful. It will be awhile before I get back to you, but I will let you know. I have told myself for several years now that I need to be done with anything eBay. The seller stated that it's of a type commonly used on "guide scopes". Perhaps I can find a trashed 50 mm finder with good back plate on it. :p

#14 Kunama

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Posted 21 January 2014 - 07:30 PM

John It would help if we knew what it is you want to attach this focuser to, ie thread on your scope.
There are several stepdown rings that have M46 p 0.75 threads but they usually fit common camera filters M52, M55, M62 etc.

I went through a similar situation recently trying to fit an SCT 2" 24tpi threaded item to a Tak FS60 (M55.9 x0.75 thread) in the end I got a Takahashi extension tube and had a 2" SCT thread cut to the other end of it.

#15 john gabriel

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Posted 21 January 2014 - 08:26 PM

John It would help if we knew what it is you want to attach this focuser to, ie thread on your scope.
There are several stepdown rings that have M46 p 0.75 threads but they usually fit common camera filters M52, M55, M62 etc.

I went through a similar situation recently trying to fit an SCT 2" 24tpi threaded item to a Tak FS60 (M55.9 x0.75 thread) in the end I got a Takahashi extension tube and had a 2" SCT thread cut to the other end of it.

Hi Kunama,
A reasonable question you ask. But I've been asking the question in reverse: "What, if anything, will this focuser thread into? Please tell me."

When you say, "There are several stepdown rings that have M46 p 0.75 threads..", I'm betting you probably mean male M46 x 0.75, not female. Please tell me I'm wrong! :jump: I want any female M46 part, so that I can modify it to mount on a base plate of my own construction. I just want the female M46. My telescope has no ready-made threads of either gender to mount the focuser on.

The focuser will then thread into my DYI base plate (made from wood or metal plus any female M46 that I can get my hands on!) on the side of my 7" newt OTA.

I only bought the focuser because the seller made the application sound common. Now I see that this is not turing out to be the case.

#16 Kunama

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Posted 21 January 2014 - 09:08 PM

John, You're WRONG ....... and I know that is what you want to hear >>>>
an M46 STEP-UP ring is male 46 however lets say you get a SD72-46 Stepdown Ring you get a female M46 thread and a male M72.

With the SD72-46 just file the external M72 thread down to smooth then
flush mount it to your scope's backplate with some stainless steel cap screws ......... and Hey Presto !!!

See the link for a chart of all the SD rings:

http://www.ebay.com....6mm-Thread-N...

http://midopt.com/as...epDownRings.pdf

#17 john gabriel

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Posted 22 January 2014 - 12:31 PM

Oh, HURRAH! I'M WRONG! I'M WRONG! :whee: :yay: :jump: :bow:

Thank you so very much, Kunama! I'll be following those links and getting on the track of that SD72-46 soon. (Hmmm... just checked those and it looks like I am in design mode again. What I want to do is definitely "do-able" from here... )

I should thank not only you, but all the others who have patiently waded through my clumsy explanations about what it is that I am trying to do. Communication is an art! (and I can never stop learning)
Cheers!
John






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