How to Use a Mortise Bit

Written by chris baylor
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How to Use a Mortise Bit
Some drill presses have an attachment that can accept a mortise bit for drilling square holes. (Jupiterimages/ Images)

Some drill presses have an optional attachment that can be mounted on the drill press spindle that allows for a mortise bit to be installed for drilling square holes. A mortise bit consists of a four-sided chisel that is hollow in the middle, allowing for a drill bit to rotate in the centre. When you use a mortise bit, the drill bit in the centre removes most of the material, and the mortising chisel cleans up the corners.

Skill level:

Things you need

  • Drill press
  • Chuck key
  • Drill press mortising attachment with hold-down clamp
  • Square mortise chisel and drill bit
  • Allen wrenches

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  1. 1

    Turn off the power switch on the drill press. Loosen the chuck with the chuck key, and remove any bit in the chuck.

  2. 2

    Set the drill press operating speed to about 1,200rpm. Refer to the chart in the head stock of your drill press, and set the pulleys to the closest speed to 1,200rpm.

  3. 3

    Loosen the clamping screw on the mortising attachment with an Allen wrench, and slide the attachment over the collar of the drill press. Tighten the clamping screw to secure the attachment to the collar.

  4. 4

    Place a mortising chisel with a bit into the mortise attachment, and tighten the locking screw to hold the chisel in place. Then, insert the end of the drill bit into the chuck, and position the drill bit so that it is protruding just slightly below the bottom of the chisel. Tighten the chuck with the chuck key to lock the bit in place.

  5. 5

    Adjust the table height of the drill press so that the bit is about an inch higher than the board to be cut. Then, adjust the depth stop of the drill press plunge mechanism to the desired depth of the mortise.

  6. 6

    Position the board beneath the mortising bit on the drill press table. Adjust the height of the hold-down clamp on the mortising attachment so that it is riding just above the surface of the wood.

  7. 7

    Turn on the drill press. Align the board beneath the bit, and plunge the bit downward into the board until you reach the depth stop. Raise the bit, slide the board to the next cut, and plunge again. Continue until the entire mortise has been cut.

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