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Thread: Compound Retaining Nuts

  1. #1
    Foamer
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    Compound Retaining Nuts

    I've just received a 130mm f6.8 Dagor from ebayer Cupog. The shutter speeds were uniformly very slow, so I took the lens off the attached lens board, unscrewed the piston caps, and swabbed the cylinder out with several cotton swabs. Reassembled--problem solved. However, when I went to put the lens back on the board, the retaining nut cracked off at the spanner wrench slots at 12 & 3 o'clock. It looks to be cheap pot metal in the nut. Maybe they had a shortage of good steel around WW1 when the lens was made. Anyway, the nut will tighten somewhat, but I don't want it breaking again. Is there a source for replacement nuts? I had another idea: dab some latex caulk or silicon rubber gasket goo around the back of the shutter (fairly small amounts) and then tighten up the broken nut. Any advice here? Other than this problem (which I've never had before), the lens is in excellent shape! Thread diameter of the shutter (where nut attaches) is 32.25mm.


    Kent in SD
    Qui sedes ad dexteram Patris,
    miserere nobis.

  2. #2
    8x10, 5x7, 4x5, et al Leigh's Avatar
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    Re: Compound Retaining Nuts

    Quote Originally Posted by Two23 View Post
    Thread diameter of the shutter (where nut attaches) is 32.25mm.
    Hi Kent,

    Modern retaining nuts have a sleeve that fits down into the hole on the lensboard, so the required hole diameter is larger than the actual thread diameter by 1 or 2 mm.

    Does your retainer have that sleeve, or is it just a flat threaded disc?

    - Leigh
    If you believe you can, or you believe you can't... you're right.

  3. #3
    Foamer
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    Re: Compound Retaining Nuts

    Quote Originally Posted by Leigh View Post
    Hi Kent,

    Modern retaining nuts have a sleeve that fits down into the hole on the lensboard, so the required hole diameter is larger than the actual thread diameter by 1 or 2 mm.

    Does your retainer have that sleeve, or is it just a flat threaded disc?

    - Leigh

    It's not simply flat. It has a raised edge that fits into the hole on the board. The threading is on the inner side of the raised edge/sleeve.


    Kent in SD
    Qui sedes ad dexteram Patris,
    miserere nobis.

  4. #4
    8x10, 5x7, 4x5, et al Leigh's Avatar
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    Re: Compound Retaining Nuts

    Quote Originally Posted by Two23 View Post
    It's not simply flat. It has a raised edge that fits into the hole on the board.
    The threading is on the inner side of the raised edge/sleeve.
    Hi Kent,

    That's just like rings on modern shutters.
    The lensboard hole diameter should be a hair larger than the outside diameter of that sleeve.

    Yours sounds like a modern Copal #0, with a 32.5mm thread and a 34.8mm lensboard hole.
    I believe you can get those from S K Grimes: http://www.skgrimes.com/products/mounting-flanges

    - Leigh
    If you believe you can, or you believe you can't... you're right.

  5. #5

    Join Date
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    Re: Compound Retaining Nuts

    Quote Originally Posted by Two23 View Post
    I've just received a 130mm f6.8 Dagor from ebayer Cupog. The shutter speeds were uniformly very slow, so I took the lens off the attached lens board, unscrewed the piston caps, and swabbed the cylinder out with several cotton swabs. Reassembled--problem solved. However, when I went to put the lens back on the board, the retaining nut cracked off at the spanner wrench slots at 12 & 3 o'clock. It looks to be cheap pot metal in the nut. Maybe they had a shortage of good steel around WW1 when the lens was made. Anyway, the nut will tighten somewhat, but I don't want it breaking again. Is there a source for replacement nuts? I had another idea: dab some latex caulk or silicon rubber gasket goo around the back of the shutter (fairly small amounts) and then tighten up the broken nut. Any advice here? Other than this problem (which I've never had before), the lens is in excellent shape! Thread diameter of the shutter (where nut attaches) is 32.25mm.


    Kent in SD
    This glass is mounted in a Compound shutter? If so, S.K.Grimes has or makes flange mounts or "nuts" for Compound shutters. Until then, you can use one of the epoxy repair kits you can find in any store. Coat threads with Vaseline, screw nut part way on, inject epoxy repair stuff in the two breaks. Let it sit for 24 hours, then unscrew it and clean off the Vaseline from the threads, screw the nut back on AND DO NOT OVER TIGHTEN IT!!

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