Trick: Drilling Perpendicular Holes

A “Trick of the Trade” from the February 2011 issue of Popular Woodworking Magazine:

Here
is a trick that I’ve developed to help keep holes perpendicular to the
surface when drilling by hand, either with a brace and bit or with an
electric drill.

I’m not very good at lining up my drill with a
try square, so I made a fixture that I call a “mirror gauge.” It’s made
from two pieces of 1/2″ MDF – one board is 5″ x 7″ and the other is
5-1/2″ x 7″. The two pieces are butt-joined with glue at 90º.

Cut
two pieces of inexpensive mirror slightly smaller than the boards, then
glue them to the faces of the MDF with mastic or mirror adhesive. I
drew perpendicular vertical lines in the middle of each mirror with a
marker. The lines provide a reference so you can see when the bit is
perfectly straight.

You can also use the mirror gauge for squaring chisels when dovetailing or mortising.

Walter Lees
Tempe, Arizona

4 thoughts on “Trick: Drilling Perpendicular Holes

  1. Makita

    I always have the same problems with the drills, sometimes is just impossible to make a straight line. I am not sure if that trick would work for me, but I am definitely going to try it. Thank you for the post.

  2. Glen

    Ashly – Walter suggests the trick for braces, but being the power guy, I ran with what I know best. You can do the larger mirrors, or how about shorter mirrors that are longer? Give it a try and let us know what works better.

  3. andy

    This is an old trick. I learned it a while back from a timber framer in North Minneapolis.
    http://tfguild.stores.yahoo.net/midrgu.html
    It’s actually amazingly accurate. You can hit within a 1/32" when drilling through a 12" timber. The TF guild mirrors are really nice.
    Drilling into the mirror makes lining things up much easier. I’m not 100% sure but I think the mirror doubles the error making it really easy to get it dead on.

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