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Thread: Screw Cutting

  1. #1

    Screw Cutting

    I'm considering switching moderators to something lighter than a northstar. I tried a friend's Atec CMM4, which required a lot more effort to tighten the final few turns than my existing moderator. The screwcutting was done by Steve Kershaw, so I've no concerns about the workmanship. The thread is 1/2 UNF.

    The paperwork from Jackson Rifles mentioned that there should be a degree of play until the final tightening of the moderator, and if this isn't the case the thread should be recut looser.

    Your views would be appreciated, as I don't really want to bother having the thread altered.

  2. #2
    Steve Kershaw cuts threads very snuggly, if there is a discrepancy in tolerances between the mod and the rifle, I would get the mod adjusted and leave the rifle thread as is.

    Any time I have been getting Steve to cut threads, I send the moderator along with the rifle, he will match one to the other, and it will be done properly.
    Brian.

    Just because you are paranoid, doesn't mean they aren't out to get you......

  3. #3
    Brian, thank you. I am at the other end of the country to Steve Kershaw, so it wouldn't be easy getting the rifle back to him. I've spoken to Nigel Teague who will re-tap the moderator thread if needs be. I'm otherwise impressed with the Atec, so will probably buy it if I can get this sorted out.

  4. #4
    It amazes me this screwcutting and the variations I am seeing in size and fit. the specs of threads and their tolerances were set out well over 100 years ago but this seems to have by-passed the gun trade. Both BSI and ISO plus the American standards authority have such tolerances laid down. The 1/2" UNF is of course an American thread and gauges have been made in this country for it since it's introduction and adopting in British manufacturing. These re laid down in place like the Machinery handbook, the little Zeus booklet that most machinsits have at leas one copy of.

    The threads and their effective diameter can be checked with gap gauges, a special ring gauge of wires and a micrometer. The threads in the moderators are usually checked with a go-no-go plug gauge.

  5. #5
    The thing that amazes me is that any one would advocate a certain degree of slop in the threads........
    Brian.

    Just because you are paranoid, doesn't mean they aren't out to get you......

  6. #6
    Quote Originally Posted by Claret_Dabbler View Post
    The thing that amazes me is that any one would advocate a certain degree of slop in the threads........
    Yes, you can envisage it shooting looose after a few rounds.

  7. #7
    Quote Originally Posted by Moonraker68 View Post
    Yes, you can envisage it shooting looose after a few rounds.
    and we all know what that will do to your zero!!

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