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Pilot holes for large drill bits

Discussion in 'Wood / Woodwork / Carpentry' started by stealthwolf, 23 Sep 2018.

  1. stealthwolf

    stealthwolf

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    I used a 20mm forstner bit to give me a well 10mm deep. I need to drill a 10mm wide hole through the timber (45mm thick).

    I used a 3mm wood bit so it would centre perfectly. On a test piece, using the 6mm wood bit next meant the hole was off centre. So on the main work, I used a 6mm hss bit which worked. But when I used 8mm and then 10mm, the edge of the hole became splintered.

    How do I avoid this?
    What was the correct technique for what I wanted to achieve?
    Should i have drilled the hole first and used a forstner bit second?
     
  2. Tigercubrider

    Tigercubrider

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    The edge of which hole? The small hole inside the well? Or where it comes out?
    If out, then add a piece of wood under the main timber, preventing break through damage
     
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  4. stealthwolf

    stealthwolf

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    I should have taken a pic.

    The forstner “hole” is a recess for the collar of a masonry bolt to rest on. That bit is fine.

    The main hole for the shaft of the bolt is chipped on the forstner side. I used a scrap bit of wood for the opposite side and there’s no breakou.
     
  5. Notch7

    Notch7

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    Drill 20mm counterbore first.

    Thrn drill 10mm hole.

    Dont drill 3mm pilot hole or increase in increments -you will end up off centre.
     
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