How to Make and Use a Drill Guide

Two Methods:Make the Drill GuideUse the Drill Guide [5/8” holes]

Bolting post caps to both the post and beams can be an effort in frustration. It is near impossible to bore the holes completely perpendicular to the surface of the post cap so that it aligns with the hole on the other side unless you use a drill press. In most cases that is a little impractical.

The usual method relies on you best effort from each side. This can be assisted with a level on the drill motor which most modern drill motors now have. That however won't keep the drill perpendicular right to left. They do make drill guides, but they are designed to replace drill presses, and don't work well at the top of a post.

Most large post caps have either 1/2” or 5/8” holes, and the following tool it design to work with either.

Method 1
Make the Drill Guide

  1. 1
    Screw the flange to the 3”x12” board off center about 2”, so you have a long end and a short end
  2. 2
    Thread the nipple into the flange.
  3. 3
    Drill through the pipe, flange, and wood with a 9/16” 12” drill.
  4. 4
    Enlarge the outside of the hole to 5/8” to a depth of 1/4”
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    Place a 1/2” bolt through the 1/2” x 1/2” copper pipe and pound it into the wood until just a 1/4” of the pipe extends beyond the surface of the wood.

Method 2
Use the Drill Guide [5/8” holes]

  1. 1
    Line the 1/4” extended copper pipe with the hole in the post cape
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    Clamp the flat wood to the post cap in two places, being careful to keep it flat against the metal post cap and not leaning against the wood.
  3. 3
    Using the 9/16” drill bore a hold into the beam by extending the drill through the pipe, flange, flat board, and 1/2” copper pipe. Bore for a few inches and then withdraw the drill to empty the shavings. Repeat until the drill motor reaches the end of the galvanized nipple.
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    Repeat on all holes (usually 4) and then do the same thing on the other side of the beam.
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    Remove the drill guide and enlarge the holes to 5/8” by re-boring with a 5/8” drill.


  • The first time you drill a hole the inside diameter of the copper pipe with be slightly increase, so move slowly through that part of the tool.
  • You could use a longer drill and not bore both sides, but you double your chance of not hitting the hole.

Things You'll Need

  • 1/2” pipe flan
  • 3”x 1/2” galvanized nipple
  • 3”x12” flat hardwood board
  • 3/4” wood screws
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    1/2” copper pipe cut to 1/2”
  • 5/8" drill 6 inches (15.2 cm) long
  • 9/1" drill 12" long
  • 1/2" drill motor
  • clamps

Article Info

Categories: Tools