Tip 1: Use a sharp saw blade
There are perfect miters—and then there are miters that have been
tweaked to look perfect. You can learn how to do both with the right
tools, a few pro tips and a good dose of patience. We can’t help you with
the patience, but we can show you tips and techniques for cutting, fitting
and joining perfect miters, along with a few tricks for making those less-than-
perfect miters look their best.
Choosing the right blade for your miter saw, and making sure it’s
sharp, are crucial for cutting tight-fitting miters. You can’t cut perfect
miters with a dull blade, one with too few teeth or one that’s
designed for ripping. Check your blade for sharpness by cutting
a 45-degree miter on a 1x3 or larger piece of oak or other
hardwood (photo). If the blade cuts smoothly with
very little pressure and leaves a clean,
almost shiny cut with no burn marks,
it’s sharp enough to cut good miters.
When you check your blade or shop
for a new one, here’s what to look for.
First, it should be labeled as a “trim” or
“fine crosscutting” blade. A 10-in. blade
should have at least 40 teeth, a 12-in.
blade at least 60. If the blade is for a
sliding miter saw, be sure the teeth have
a hook angle of zero to negative five
degrees. Teeth with a neutral or negative
hook angle are less aggressive and
safer for sliding miter saws. Expect to
spend at least $50 for a carbide-tipped blade that’ll perform well and last.
Sharp vs. dull blade comparison
Sharp Blade vs. Dull Blade Comparison
Sharp blades have crisp, keen points and edges. Dull blades have worn or broken teeth and often a crud build-up.
Tip 2: Tweak the cut
Even on perfectly square corners, 45-degree angles won’t
always yield perfect miters. Wall corners can be built up
with corner bead and compound, and window and door
frames can slightly protrude or be recessed behind surrounding
drywall. That’s when you have to start fiddling
with the angles to get a tight fit.
In most cases, you’ll be making adjustments as small as
a quarter of a degree. If the gap is small (about 1/16 in.),
recut one side of the miter (Photo 2). If the gap is larger,
you’ll have to recut both boards or the trim profiles won’t
line up. For more tips, type “tight miters” into the search box above.
Tip 3: Glue and sand for a seamless fit
Here’s a trick to make miters look great, but it only works
if you’re installing raw trim that will get finished after
installation. It’s easy. Glue the joint, then sand it smooth.
The sawdust from sanding will mix with the glue to
fill any small gaps. Sanding the miter will also even out
any slight level differences and make the job look more
professional. Don’t try to fill large gaps, especially in trim
that’ll be stained. Glue-filled gaps absorb stain differently
than the surrounding wood and will stick out like a
Tip 4: Burnish the corner
You can make less-than-perfect miters on outside corners
look their best with this tip. If your baseboard or crown
molding has a slight gap in the outside corner miter, you can
hide it by rubbing the tip of the miter with the shank of a
screwdriver or nail set. The bent fibers will disguise the gap,
and the slightly rounded corner will be less likely to get
chipped or damaged.
The best way to prevent this problem is to cut your outside
corner miters about 1 degree sharper than the actual
angle so the tips of the miters touch. This will leave a tiny
gap at the back of the miter where it’s barely noticeable.
Tip 5: Fit one miter at a time
Whether you’re edge-banding
a tabletop as
we’re showing here, trimming
out a window or
door, or installing baseboard,
it’s always best to
fit one miter at a time
whenever possible. Start
with a scrap of molding
with a miter cut on it as a
test piece. When
you have the first miter
fitting perfectly, mark the
next one (Photo). Then
cut and fit the adjoining
miter before you nail
either piece. For edge
banding, work your way
around the project using
the same process for each
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Tip 6: Guess and test
There are all kinds of
ways to find odd angles,
but most carpenters simply
make a guess and then
cut a pair of test pieces to
see how lucky they are.
The angle of these two
walls looks to be less than
45 degrees. A good guess
would be about 30
degrees. Divide 30 by two
to arrive at the miter
angle, and cut a couple of
scraps at 15 degrees. Here
there’s a gap in front, so
we need to increase the
angle slightly and recut
the scraps at 16 degrees.
When you’ve zeroed in on
the correct angle, the
scraps will fit perfectly,
and you can then cut the actual moldings.