Protractors and
Miter- Saw Gauges
Gary Katz
Figure 1. Reading an angle with a protractor or angle finder is easy, but transferring that angle to a miter saw
can be a nightmare.
IT’S EASY TO READ ANY ANGLE with
a protractor, and easy, too, to split
that angle in half in order to determine the correct miter. [Fig. 1]
But it’s not so easy to transfer that
angle to a miter saw. Why? Probably because the first miter saws
were designed by engineers, not
carpenters, and the numbers on
your miter gauge are actually the
complementary numbers for every
angle you’re cutting.
For those of you who are still
as confused as I once was, before
I get to the solution, let me explain
the problem.
If you set your saw at “0,”
you’re actually cutting a 90° angle
(a butt cut); that’s the angle of the
From Mastering the Miter Saw DVD
90°
Figure 2. We all know that this is a
90° angle.
45°
Figure 3. And we know that this is
a 45° angle.
©2004 Gary Katz, OnSite Productions, LLC
fence to the blade. [Fig. 2] If you
swing your saw to 45°, you’ll be
decreasing the angle between the
fence and the blade and cutting an
acute angle. [Fig. 3] As you swing
the saw toward the fence, the
angle gets smaller, more acute,
right? So why do the numbers on
the gauge get bigger?
Let’s not go there — yet!
Instead, remember that your fence
is set at 90° to the blade (when the
miter-saw gauge reads 0), which
means that the more you swing
your blade toward the fence, the
more you’re subtracting from 90°.
To resolve the confusion forever,
take a permanent marker and write
down the correct angles on your
www.garymkatz.com
page 1
Figure 4. True Miter-saw Angles
To avoid confusion, write the correct angles
(shown here in red) above the numbers that
appear on a standard miter-saw gauge.
Miter-saw fence
Blade
30
60
30
60
4
45 5
45 5
4
67 1
22 1 ⁄2
⁄2
6
30 0
60 0
3
miter-saw gauge, above the ones
that are already there, ie.: 0 = 90;
10 = 80; 20 = 70; 30 = 60, etc.
[Fig. 4] There are a few saws on
the market that are manufactured
with the correct angles; the new
Bosch 10-in. 44-10 is one of them.
And yes, that’s right, the
221 ⁄ 2° mark on your gauge is
really a 671 ⁄ 2° angle! That’s one
of the reasons we’ve all been confused for so long. In the future,
when you see an angle like the one
in Fig. 5, try to think of it as a
135° angle — the miter angle is
671 ⁄ 2°.
And remember, if you want to
cut a sharper, more acute angle,
swing your saw past 45,° where
the angles get sharpest. [Fig. 6]
Most saws will cut at least to a 40°
angle. My Bosch miter saw will
cut 30° to the right and 40° to the
left.
So, what happens when you
put an acute-angle jig on your
miter saw? You’re simply changing the angle of the fence to the
blade. [Fig 7] With an acute-angle
jig made at a 45° angle, the saw
fence is set at 45°, so the more you
swing the blade toward the fence,
the more you’re subtracting from
45°. You can even use the “confusing” numbers supplied by the
saw manufacturer by doing the
math backwards: If you want to
cut a 15° angle, subtract 15 from
45 and set your saw at that difference: 30.
75
15
90
0
Figure 5. We’ve all learned the hard way that
this angle requires 221 ⁄ 2° miters. But this is
really a 135° angle and requires 671 ⁄ 2° miters!
75
15
1 ⁄2
67 1 ⁄ 2
22
Figure 6. After all, a 221 ⁄ 2°
angle would look like this!
Figure 7. This acute-angle jig effectively shifts the angle between blade
and fence from 90° to 45°.
From Mastering the Miter Saw DVD
©2004 Gary Katz, OnSite Productions, LLC
www.garymkatz.com
page 2