The secret for a glove-tight fit for trim corners is a coped joint. With this technique you can even make complex crown moldings fit without leaving gaps. Because inside corners are rarely square, simply butting two mitered pieces into the corner almost always looks lousy. The only foolproof method for great-looking inside corners is cutting a coped joint. This age-old carpenter's trick involves cutting the profile on the end of one molding and fitting it against another like pieces of a puzzle. The resulting joint is easy to file and sand for a perfect fit, even on out-of-square corners. In this article we'll walk you through the key techniques, step by step, and you'll be cutting perfect copes in no time.
The 45-degree cut will—through the magic of geometry—provide a perfect profile to guide your coping cut. When you make the miter cut, leave the baseboard a couple inches too long. You can cut it to final length after the coping is done.
Follow the profile created by the miter cut. Relief cuts at tight turns allow waste to fall away and your saw to make turns more easily. You can make straight cuts faster and better with a miter saw (more on that later).
Your coping cut doesn’t have to be perfect. Even the best trim carpenters use files, rasps and sandpaper to clean up their cope cuts. Tight curves, for example, are almost impossible to cut with a coping saw. But a small file rounds them easily.
Keep a scrap of the trim handy so you can check the fit as you fine-tune the cope. With really complex profiles, you may have to check and fine-tune the fit a dozen times before you get it right.
Since the most commonly coped molding is baseboard, we’ll use that as our example. Begin by butting the side that won’t be coped into the corner and nail the baseboard in place. Now you’re ready to cope the other baseboard. There are four basic steps.
You can make perfectly fine copes using just a miter saw, coping saw and file. But there are ways to speed up the process without sacrificing accuracy. In fact, you can increase accuracy and work faster.
Start out straight upBaseboard often tilts inward at the bottom because of the drywall’s tapered edge. And that makes coping tricky. To avoid trouble, make sure the baseboard sits square to the floor. If it tilts, remove it and drive a screw into the framing near the floor. Leave the screw head slightly proud so it holds the baseboard away from the wall. Then check again with your square. You may have to turn the screw in or out a little to get the baseboard to stand straight up.
Brighter is betterWith good lighting, you’ll get faster, better results. So take a minute to set up a work light or move your workstation near a window.
Clamp it downCoping thin, floppy trim is like doing dental work on a snake. A clamp or two will hold your work steady and your result will be much more precise.
Coping saw setup
If you’re using your grandpa’s coping saw—well, actually any coping saw—do three things:
What's a coped corner?
In a coped corner, one molding has a square cut on the end that butts up against the wall. The other molding has a coped cut that fits perfectly against the face of the first molding.
Why do it?
A coped corner fits tightly, even if the walls are out of square (and they usually are). Coped trim also stays tight—even when the wood shrinks, the walls shift or the vacuum cleaner whacks it.
Why not miter?
Cutting both pieces of trim at 45 degrees makes sense in theory. But in the real world, two walls rarely form a perfect 90-degree angle. So getting two miters to meet tight and right is challenging or impossible. And even if you get it tight, the joint will probably open as wood naturally shrinks or swells. Coped corners take these elements out of play.
Cut the “straightaway” with a miter saw for a faster, straighter cope. Turn the molding upside down, set your saw at least 5 degrees to the right and cut straight down until you hit the curvy part. Some pros even nibble away at curved profiles with a miter saw.
Coping cuts often create thin, pointy tips on the trim. Support those tips with your finger as you cut, file or sand to prevent them from splintering off.
A narrow, fine-tooth blade cuts curves much faster than a coping saw. It’s also a fast way to wreck your cope. So practice on scraps before making real cuts.
Tools that match the curves of a profile make coping faster and better. On complex profiles, I sometimes use a file, rasp, rotary tool or dowel wrapped with sandpaper—or all of the above.
With simple ranch-style moldings, you may not need a coping saw at all. Cut the straight section with a miter saw, then cope the curve with the rounded nose of a belt sander. Belt sanders also help out on some styles of crown molding.
When starting a cut, make a few light pull strokes to create a groove before you saw away in earnest. On really hard woods like maple, your blade might skid off the mark. In that case, cut a tiny starter notch with a utility knife.
Always ‘back bevel’
If you look closely at these photos, you’ll notice that all the cope cuts are made at an angle. That leaves a pointed edge along the profile. And that pointy edge has a few advantages: First, it allows the cope to fit tightly in out-of- square corners. Second, sanding or filing the cope is easier because you have less material to remove. Finally, that pointy edge will crush inward a little when forced against the adjoining trim, so you’ll get a tight fit even if the cope isn’t perfect. The best angle for a back bevel varies. On baseboard, 5 degrees is often enough. On crown molding, shoot for 45 degrees or more.
Don’t worry about your backside
Remember: The face of the trim is all you care about. Don’t be afraid to hack away the back with steep back bevels or ugly cuts from different angles. An ugly back side often means a good cope.
Highlight the profile
If you can’t see the profile clearly, rub your pencil across it to create a perfect guideline.
Guide the blade with your thumbnail to start the cut accurately. If your molding has a little flat spot on top like ours, start the cut with the blade of the coping saw held perpendicular to the molding to make a square starting cut.
Angle the coping saw about 30 degrees to remove more wood from the back of the molding than the front. Then slowly and carefully saw along the profile. Concentrate on staying just outside the line. You can always sand or file away extra material.
Restart the cut to saw around sharp curves or to cut out notches. Complex shapes like this may require three or four approaches at different angles.
File or sand off high spots. Use rolled-up sandpaper or a rattail file to fine-tune curved sections. Continue checking the fit, then filing or sanding until the joint fits tight.
The first step in coping is to establish the cutting line. Cutting a 45-degree bevel is the easiest method if the two moldings you're joining have the same profile. The molding shown has a complex profile, making for a challenging coping job. Most of the moldings you'll encounter will be considerably easier. Crown and cove moldings that rest at an angle against the wall and ceiling require a slightly different beveling technique to reveal the profile for coping.
Photo 5 shows you how to start the cope. The technique varies slightly depending on the profile of the molding. Moldings like ours with flat spots on the top require a square starting cut. If you start angling the cut too soon, you'll see a little triangular gap on the top of the moldings when you join them. Cut a practice cope on a scrap to confirm your starting angle.
Clamp the molding to a sawhorse or hold it in place with your knee while you saw. Don't force the blade. If the blade starts to leave the cutting line, back up a little and restart the cut. On steep curves, the frame of the saw may hit the molding. If this happens, back the saw out of the cut and saw in from the opposite direction.
You may be able to complete some simple copes with one long cut, but in most cases you'll have to approach them from two or three different angles to finish the job (Photos 6 and 7).
After a few minutes of sawing, the cut will be complete; now it's time to test-fit the cope on a matching piece of trim. Some copes fit perfectly on the first try. Others require several more minutes of filing and sanding before you get a good fit (Photo 8). If the joint is close to fitting, you'll only need to touch up the high spots with 100-grit sandpaper. Use files to remove larger amounts of material.
Position your crown molding upside down in the miter box at the angle it will rest on the wall (flat spots tight to the bed and fence). Screw or clamp a stop to the extension table to support the crown molding at the correct angle.
Cope crowns at a sharper angle. Recut areas that are hitting in the back. It's common to have to remove large amounts of material in some areas to get a tight fit.
Measure and cut the end of the first crown molding square. Butt it into the corner. Don't nail within 16 in. of the corner. Cope the second piece of crown molding and file and sand it for a perfect fit.
Photo 9 shows you how to position the crown molding upside down in your miter box for cutting the bevel. Attach a wood stop to the extension table to hold the molding at the correct angle. Sawing copes on crowns, especially large ones, requires more effort because the angle of the cut has to be about 50 degrees—much steeper than for a baseboard cope. Even experienced carpenters cut this angle too shallow once in a while. Usually one or two areas will hit in the back and you'll have to remove more material (Photo 10).
Switch to a blade with fewer teeth for cutting thick materials like crown moldings. Then expect to spend 10 or 15 minutes on each joint to get a perfect fit. Before you tackle crown molding copes, practice on smaller moldings like base shoe or simple baseboards to gain confidence. Once you've mastered coping you'll never miter an inside corner again.