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Drill size to tap and use a 5/8" bolt

Discussion in 'The Garage' started by Mudstud, Dec 30, 2002.

  1. Mudstud

    Mudstud 1/2 ton status

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    Drill size to tap and use a 5/8\" bolt

    I have a 5/8th threaded bolt (pitch 11) and I need to drill and tap a hole for it. What size drill bit do I use for the hole? Is there a simple rule of thumb to go by when drilling/tapping holes?
     
  2. SkulzNBonz

    SkulzNBonz 1/2 ton status

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    Re: Drill size to tap and use a 5/8\" bolt

    9/16 th's. A good rule of thumb is a 16'th smaller, especially when drilling with a hand drill.

    John
     
  3. Triaged

    Triaged 1/2 ton status

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  4. SkulzNBonz

    SkulzNBonz 1/2 ton status

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    Re: Drill size to tap and use a 5/8\" bolt

    Most charts say 1/32" smaller. The downsides to this are drillbits that are sized in 32's are $$$$$, and when using a hand drill you wobble a little, making the hole slightly larger than the stated size of the drill bit. A 9/16th bit will work fine.

    John
     
  5. JK5

    JK5 1/2 ton status GMOTM Winner

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    Re: Drill size to tap and use a 5/8\" bolt

    By using a 9/16 insted of 17/32 will give you less thread to work with....especially if your hand drilling.....Not a good idea...stick with the chart. If your looking for a drill and tap try: www.mcmaster.com
     
  6. SkulzNBonz

    SkulzNBonz 1/2 ton status

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    Re: Drill size to tap and use a 5/8\" bolt

    Doh! I was tinkin' 19/32" /forums/images/graemlins/rolleyes.gif

    John
     
  7. Triaged

    Triaged 1/2 ton status

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    Re: Drill size to tap and use a 5/8\" bolt

    So then you would use a 1/2" drill bit? Sounds reasonable.
     
  8. SkulzNBonz

    SkulzNBonz 1/2 ton status

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    Re: Drill size to tap and use a 5/8\" bolt

    Normally, when I drill and tap a hole, I go a 1/16th smaller, but most of the time that is with a 1/2" or smaller bolt, so the threads are not going to be that deep. I would assume (I hate doing that) that drilling with a 1/2" bit and tapping to 5/8" would work, but I would be awfully cautious as not to break the tap. A broken tap can be a nightmare.

    John
     
  9. TONYP

    TONYP 1/2 ton status

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    Re: Drill size to tap and use a 5/8\" bolt

    use the chart Triaged put up.....you need to use the standard..... /forums/images/graemlins/k5.gif
     
  10. gmule

    gmule 1/2 ton status

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    Re: Drill size to tap and use a 5/8\" bolt

    37/64th is the drill size you need
     
  11. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    Re: Drill size to tap and use a 5/8\" bolt

    It's all about the amount of thread contact you want....a friend of mine is a machinist and described it to me once (though I didn't fully understand all of it)

    The smaller you can drill the pilot hole (and the more precisely!) the sharper the edges of the threads will be....I think there is even a specification for different amounts of thread contact area on machinists drawings...?

    Anyway I just think of it as the larger the pilot hole, the more "squared off" the tapped threads will be, and hence the less strong they will be.

    If possible, use the bit in the drill guide and drill the hole in with a drill press (vs. hand drill)...if it is a critical connection point....

    /forums/images/graemlins/smile.gif
     
  12. boots

    boots 1/2 ton status

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    Re: Drill size to tap and use a 5/8\" bolt

    from my machinist manual on CD

    TDS=OD*1/n
    TDS= Tap Drill SIze (in inches)
    OD = Outside Diameter
    1 = constant
    N = number of threads per inch

    NOTE: THis formulas will determine a recommended decimal size, then use numbered, lettered, or fractional size drill that is closest to the computed size
     

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