Cross threaded crane lock screw
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Thread: Cross threaded crane lock screw

  1. #1
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    Cross threaded crane lock screw

    I bought a cobra made in 1956 that wasn’t working. I got it functioning correctly but someone in the past cross threaded the crane lock screw. The crane lock is holding the crane in the frame but the screw is not flush with the frame. I can live with the crane lock screw sticking out but would like for it to be flush.

    Is there a larger crane lock screw that the frame could be taped out for?

    Does anyone know what the frame thread size is? Maybe I can clean up the threads in the frame.

    Any other suggestions?

    Thanks in advance.


    Sent from my iPad using Tapatalk

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    To find out what the threads are you can use a thread gauge and measure the diameter of the crane lock screw.
    Well I suppose that I could do that too.

    IMO the crane lock screw is: .244 diameter x 40 TPI. 1/4 x 40 (?)
    Last edited by kenhwind; 10-23-2019 at 08:50 AM.
    Ken
    "I like Colts and will die that way"

  3. #3
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    The crane retention screw is a cap screw with a small spring and plunger under/inside it.
    The cap is not completely flush with the frame with the frame, the dome part is up, often with a partial thread showing.

    About all you can do is somehow check the threads on the cap and try to find a tap of the same size so you can try chasing the threads.
    There are machine supply companies who sell taps of about any size possible. Do an internet search for Tap and Die makers.

    An smart option would be to send the gun to Frank Glenn or Spartan and have them repair it, if it's possible.
    Both Glenn and Spartan are Master pistolsmiths on Colt revolvers, and Spartan was trained at the Colt factory.
    I would think that both have seen this before and know what can be done.

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    Brownell's: 1/4 x 40 Bottom tap.

    https://www.brownells.com/gunsmith-t...079-26046.aspx


    I will verify my measurements, but a call to Brownell's might answer the question. I'm curious as to why this tap exists unless it is for fixing this problem.



    Ken
    "I like Colts and will die that way"

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    Attempting to chase and make the threads uniform is a project that entails risk.
    Botch it and the frame is ruined, and it's way easy to botch it.

    What's needed is to get the frame in a setup so the right side of the frame is ABSOLUTELY level and at 90 degrees to the tap.
    This is tough to do because the left side of the frame is not flat or even.
    This requires a special fixture or a good drill press, unplugged and the drive belt off to hold the tap. You also need a good tapping fluid like "Do Drill" or any hardware store drilling and tapping fluid.....NOT some oil.

    If the tap and frame aren't at a perfect 90 degrees the tap will deform the threads. This means you shouldn't attempt this by holding the tap by hand. It's virtually impossible to hold the tap perfectly straight in all directions.
    You have to "finagle" the tap to get it properly started on good original undamaged threads so you can straighten out the ones that are damaged.

    Also, I highly recommend buying a new cap screw to avoid unnoticed damage to it's threads. Places like Jack First sell new cap screws.
    This will prevent a slightly deformed cap screw tread from re-cross threading the hole again. Cheap insurance.

    Always start the cap screw into the frame by hand before using a screwdriver to tighten it.
    That's a good technique for most all gun screws.
    kenhwind likes this.

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    Yes chasing threads can be a tricky situation, especially since this is an alloy frame.
    Trying to use a new crane lock screw (cap) might be the best approach.
    IIRC the difference between the "D" frame crane lock screw and the larger E & I (Python) is the length. I wonder if this the longer one.
    Ken
    "I like Colts and will die that way"

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    Quote Originally Posted by dfariswheel View Post
    Attempting to chase and make the threads uniform is a project that entails risk.
    Botch it and the frame is ruined, and it's way easy to botch it.

    What's needed is to get the frame in a setup so the right side of the frame is ABSOLUTELY level and at 90 degrees to the tap.
    This is tough to do because the left side of the frame is not flat or even.
    This requires a special fixture or a good drill press, unplugged and the drive belt off to hold the tap. You also need a good tapping fluid like "Do Drill" or any hardware store drilling and tapping fluid.....NOT some oil.

    If the tap and frame aren't at a perfect 90 degrees the tap will deform the threads. This means you shouldn't attempt this by holding the tap by hand. It's virtually impossible to hold the tap perfectly straight in all directions.
    You have to "finagle" the tap to get it properly started on good original undamaged threads so you can straighten out the ones that are damaged.

    Also, I highly recommend buying a new cap screw to avoid unnoticed damage to it's threads. Places like Jack First sell new cap screws.
    This will prevent a slightly deformed cap screw tread from re-cross threading the hole again. Cheap insurance.

    Always start the cap screw into the frame by hand before using a screwdriver to tighten it.
    That's a good technique for most all gun screws.
    This is my thoughts also.

    I was hoping for a old school been there done that answer, getcher a.....and then do.....one of them answers.

    I’ll just live with the screw sticking out of the frame since it doesn’t affect the functioning and it only cosmetic.

    Thanks again for the responses.


    Sent from my iPad using Tapatalk

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    That cap screw is .250X 40 just be careful and keep the tap straight.

    Frank Glenn
    dfariswheel likes this.


 

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