
Step 3: Mitering the Corners
Miter Joints

This is the most important step of the project. In this step,
we'll cut the actual corners for the frame. To start off, cut the
2 big pieces you have down into the 4 pieces we'll work with. Make
them longer than necessary, since we'll miter the corners. It's
easier to work with 4 shorter pieces than 2 long ones. Since the
frame will be 20" x 17.5" (outside edges), cut each long piece into
one piece that is 26 inches long, and one that is 24 inches long.
This will give you 2 of each, with 6 inches of extra material on
each piece, with 10 inches left over from each of the two big pieces
you started with.
A miter joint is a 45degree cut on both ends of two pieces
which will join to form a 90degree angle, as shown in the illustration
to the right.

Miter Joint


In order to get perfectly mitered corners in a picture frame,
you need to make sure of the following two things:
 The angle on each end of each piece must be exactly 45 degrees.
 Opposite side pieces must be exactly the same length.
I'll show you some tricks I've read about to guarantee perfect
corners.

Measuring Exactly 45 Degrees

Setting the miter fence to exactly 45 degrees


To ensure rule #1 is true, use a drafting triangle to
set your miter gauge on your table saw to exactly 45 degrees. Don't
trust the scale on the gauge itself, particularly if your saw is a
basic homeworkshop model, like mine. If it is off by even a couple
of degrees, you'll get gaps in the corners of your frame. Using a
drafting square will make obtaining a perfect 45 degree angle foolproof.

Watch out for the teeth on the sawblade. When setting the
angle, make sure that your triangle is pressing against the
blade face, and not touching the teeth at all, or else the angle
won't be perfect. My table saw has a 10" diameter blade, so I
bought a drafting triangle that is only 8" wide, so the entire
triangle can rest against the face of my blade without touching
any of the blade's teeth. This is a cheap tool (I got mine for
$5 at Staples) and will substantially improve the quality of
your frames.

Once you've set the angle, cut one end off each of your 4
pieces. Pay attention to the angle you're cutting, be mindful
of which edge is the inside edge of the frame, and which is the
outside. After cutting, the shorter edge of the wood must be
the inside edge. That is, the edge with the rabbets cut into
it. The rounded edge should be the longer edge.

Cutting the Pieces to Length
When you've cut one end off all the pieces, gather two
opposite side pieces together. We're going to cut the other
ends now, in a way that will make sure rule #2 is true. The
trick is to cut the sides in pairs. That is, the two pieces
that make up opposite edges of the frame are cut at the same
time.

Take one of the two side pieces and make a mark at 15.5
inches on the inside edge. This is where we will want the
blade to cut. Position this piece against the miter fence,
such that the mark will touch the edge of the saw blade at
just the right length. Again, pay careful attention to make
sure you're cutting the angle the right way. I've wasted a
few pieces of wood making this mistake.

Once the first piece is in just the right place such that the saw
will cut it exactly at the mark you made, stack the other side piece
on top of the first one and slide it along the bottom piece, feeling
the alreadymitered ends with your finger to make sure the pieces are
perfectly linedup.

Ensuring oppositeside pieces are exactly the same length


Clamp the pieces to the miter fence


When the mitered ends are perfectly flush with each other, clamp
the pieces against the miter fence. Use a piece of scrap wood to
prevent the clamp head from touching the actual wood, or it may
leave a mark. Make sure your saw blade is raised high enough to cut
through both pieces. Fire up the saw and make the cut. The pieces
should be exactly the same length, and the angle should be exactly
45 degrees.

Repeat this process for the frame's other two edges, which should
have inside dimensions of 18 inches.

Next: Assembling the Frame.
