Results 1 to 11 of 11
  1. #1
    Toolbert is offline Stainless
    Join Date
    Nov 2003
    Location
    Vashon Island, WA
    Posts
    1,146

    Default Optical thread reference/standards?

    I'm duplicating some lens adapters for theater "effects" projection ... and need to cut a fine internal thread to fit a German lens of probably 1970's vintage. The threads are so short it's hard to sight a good match even with my best B&S thread gages.

    The major diameter is clearly 50mm.

    The thread pitch is a tossup with the .75mm, .8mm and 32 tpi gages - I can only guess.

    Does anyone recognize this as an obvious standard, that I can consult to do it right? Any other words of wisdom?

    thanks,

    Bob

  2. #2
    kuromaku is offline Plastic
    Join Date
    Jan 2011
    Location
    Northern California, USA
    Posts
    20

    Default

    This may be completely irrelevant to your particular lens, but the old German lenses I have for microscope use have M50 x 0.75mm threads. Never heard of 0.8mm pitch, but then I haven't messed with projectors of that size.

  3. #3
    kurcules is offline Cast Iron
    Join Date
    Jun 2008
    Location
    Pasadena, CA
    Posts
    379

    Default

    I tried old and new Machinery's handbooks, no joy. I do know that threads for optical devices tend to be of a funny form so they don't get crudded up or tear out even with the fine pitches. You might have to look at 'em with some serious magnification to figure out what's going on.

  4. #4
    J_R_Thiele is offline Hot Rolled
    Join Date
    Jan 2003
    Location
    Columbia Missouri
    Posts
    644

    Default

    Any way to make a mold of them?

    If so, look at them from above with a small handheld magnifying glass and scale devices.

  5. #5
    WHHJR is offline Stainless
    Join Date
    Jun 2009
    Location
    Near:Louisville, KY
    Posts
    1,046

    Default

    The Japanese? WW-II transit that I bought has a broken eye piece. I tried all the thread gages that I had and it seemed to be around 40 or maybe 39.

    I talked to a local Instrument gentleman who suggested 40 tpi was common. I made one and it worked perfectly.


    2

  6. #6
    Porschefix's Avatar
    Porschefix is offline Cast Iron
    Join Date
    Dec 2009
    Location
    Bluff Dale, Texas USA
    Posts
    277

    Default

    Use an optical comparator to get the pitch, get it right the first time.

  7. #7
    Gary E is offline Diamond
    Join Date
    Jan 2006
    Location
    Houston, TX
    Posts
    5,897

    Default

    Quote Originally Posted by Toolbert View Post
    I'm duplicating some lens adapters for theater "effects" projection ... and need to cut a fine internal thread to fit a German lens of probably 1970's vintage. The threads are so short it's hard to sight a good match even with my best B&S thread gages.

    The major diameter is clearly 50mm.

    The thread pitch is a tossup with the .75mm, .8mm and 32 tpi gages - I can only guess.

    Does anyone recognize this as an obvious standard, that I can consult to do it right? Any other words of wisdom?

    thanks,

    Bob
    This means you have a male thread to measure?
    Use an Optical Comparator to measure it and then calculate the mating threads dimensions.

    I see Porschefix posted the idea first....and if you dont have a Comparitor, find one, companies that do a lot of threading usually have at least a 31.25 power machine with at least a 20 inch screen.

  8. #8
    Lambert is offline Hot Rolled
    Join Date
    Oct 2002
    Location
    Leiden , The Netherlands
    Posts
    589

    Default

    Since you have a male thread , how about measuring the pitchdiameter with a micrometer.
    Should be notably different for .75 and .8 mm pitch.

    I have to agree an optical comparator would give you a most undisputable answer.

    Another thought : if available time and material allow you could make some testpieces.

    FWIW : in my years in a physicslab-machineshop all the even slightly optical metric threads were either 1 or .75 mm pitch.

  9. #9
    Toolbert is offline Stainless
    Join Date
    Nov 2003
    Location
    Vashon Island, WA
    Posts
    1,146

    Default

    Folks, thanks for the replies and suggestions. Based on the above I'm sure it's M50 x .75mm.

  10. #10
    Conrad Hoffman's Avatar
    Conrad Hoffman is offline Stainless
    Join Date
    May 2009
    Location
    Canandaigua, NY, USA
    Posts
    1,748

    Default

    Who made the lenses? If it's Schneider, Rodenstock, Zeiss or some other known maker, it should be easy to look it up or inquire. I wouldn't assume the existing adapters are correct unless they were made by the lens maker. I'd take a cast of the lens itself, then cut some trial parts.

    CH

  11. #11
    Clive603 is online now Titanium
    Join Date
    Aug 2008
    Location
    Sussex, England
    Posts
    2,300

    Default

    Another vote for the optical comparator. Check the flank angles too. Whitworth (55) thread angles on mm pitches is not unknown also 47.5 BA angles on whatever the maker wanted. Another gotcha is close fits on truncated forms, e.g. 55 thread but 60 depth. Outside the standard camera, enlarger and microscope threads it really is something of a lottery especially if thin tubes are involved although 1970's seem to be the shake-out era where things settled down into something fairly logical. I had some really weird and wonderfuls in the useful bits and special kit built round it boxes in my lab when I was a wage slave.

    Clive

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •