screwholes

Discussion in 'Gunsmithing Forum' started by getting old, Apr 5, 2009.

  1. getting old

    getting old New Member

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    Why do the best gunsmiths drill screwholes slightly under the miner size of the screw tap (say .009 or so) before using the tap?
     
  2. Dillinger

    Dillinger New Member

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    My initial response would be because it gives more purchase to the threads when you tap them.

    In the shop, routinely, we drill out #6 screw holes for #8's for better, more beefy screws on the scope mounts.

    JD
     

  3. RL357Mag

    RL357Mag New Member

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    Damn! I saw this thread title and thought I was in for another "camel toe" experience...
     
  4. c3shooter

    c3shooter Administrator Staff Member

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    Why? Because it is much easier to remove metal than to put it back again! The holes for most screws are properly not the screw size, but a numbered wire size. A 8-32 screw does NOT get a 1/8th inch hole, but the # drill size smaller (#29). Dimensions are to the OUTSIDE of the threads of the screw, not to the inside (drill diameter) See chart: Drill and tap size chart - Wikipedia, the free encyclopedia

    A somewhat sloppy machinist that does not have numbered drill sizes might use a smaller bit, hoping the tap will ream the hole- but that is a great way to break taps, and they are a b!tch to get back out. Now, ask me how I know that.....
     
  5. WILDCATT

    WILDCATT New Member

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    screw holes

    most spec for drilling tapped holes are for 75% thread.so a smaller hole will give you 90/100%.I have cleaned many hole with and electric remover.age has got me and there is a name for it.I can remember how to do it but not the name darn.:rolleyes:
     
  6. Bolosniper

    Bolosniper New Member

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    Don't need to brother. Been there, done that too, and have the scars and t-shirt to prove it!