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What size hole to drill?

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  • 01-05-2009 12:34pm
    #1
    Lex Luthor
    Registered Users Posts: 11,220 ✭✭✭✭


    I want to drill out 2 holes to screw in 2 self tapping M4 screws into 1mm thick aluminium. What size holes do I need to drill?

    Does the hole need to be slightly smaller than the screw size (ie. 3.5mm) or is it a 4mm hole sufficient?


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    #2
    muggyog
    Registered Users Posts: 725 ✭✭✭muggyog


    Err to the side of too small rather than too big. A very small hole is all that is needed since aluminum is a soft material. Self tapper will make its own hole so you should probably use a 2mm bit.


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    #3
    Lex Luthor
    Registered Users Posts: 11,220 ✭✭✭✭Lex Luthor


    muggyog wrote: »
    Err to the side of too small rather than too big. A very small hole is all that is needed since aluminum is a soft material. Self tapper will make its own hole so you should probably use a 2mm bit.

    just been told that it won't be 1mm aluminium but 2mm mild steel. Big difference. Still go with the 2mm hole?


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    #4
    Joey the lips
    Registered Users Posts: 10,262 ✭✭✭✭Joey the lips


    Dont know much about the application but the clue is in the screw "Self Tapper" drill a smaller pilot hole and the screw should expand it and grip it at the same time.

    If it does not work there is always silicone :D


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    #5
    DublinDilbert
    Registered Users Posts: 5,381 ✭✭✭DublinDilbert


    Lex Luthor wrote: »
    I want to drill out 2 holes to screw in 2 self tapping M4 screws into 1mm thick aluminium. What size holes do I need to drill?

    Does the hole need to be slightly smaller than the screw size (ie. 3.5mm) or is it a 4mm hole sufficient?

    Yes the hole needs to be smaller than the tap size. The diameter of an M4 bolt is 4mm, as you'd imagine. So if you drill a 4mm hole, the bolt will just slide in!

    For most small taps you would go 1mm lower, but when you get down to the small tap size they go down to about 0.5mm below.

    So a 3.5 should be ok for an M4. If you have some spare material, drill a 3.5mm hole and tap it out and see....


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    #6
    muggyog
    Registered Users Posts: 725 ✭✭✭muggyog


    DublinDilbert wrote: »
    For most small taps you would go 1mm lower, but when you get down to the small tap size they go down to about 0.5mm below.

    I would suggest this for tapping into steel. Self tappers have a very course thread and that combined with a soft metal would suggest a smaller hole ( if you use 3.5mm you will need the silicone!)


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