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How-to Tips for Tight Miters

We demonstrate 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.

By the DIY experts of The Family Handyman Magazine

How-to Tips for Tight Miters

We demonstrate 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.

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 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 sore thumb.

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 edge piece.

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.

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Required Tools for this Project

Have the necessary tools for this DIY project lined up before you start—you’ll save time and frustration.

    • Miter saw
    • Finish nail gun
    • Wood glue

Required Materials for this Project

Avoid last-minute shopping trips by having all your materials ready ahead of time. Here's a list.

    • Sandpaper – 120-grit

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