Tight Miter joints for crown moulding

I am using an 18 inch true angle from Rockler to find the angle of my corners. The corners are reading 90 degrees, when I use a smaller angle finder the angles are off by a few degrees. The problem is wether I cut for 90 degrees or whatever angle I find I cannot get tight fits. The saw is right on and am using a Rockler jig to hold the moulding. What am I doing wrong?

Mickey:

If you don't get any better advice on what you're doing wrong, you can always resort to a technique called "sponge caulking" as a last resort.

That is, once your crown moldings are installed with all the gaps showing, you can caulk those gaps with a latex caulk and wipe them down with a damp sponge before the caulk dries. The result will be that caulk will only remain inside the gap. When you paint over that, it'll look like there was never a gap to begin with.

This is what cabinet and counter top installers do to hide the gap between the cabinet or counter top and the walls they're mounted to or butt up against.

mickey, if you go up to the search function and type in "corner miter" you will find some excellent tips from Inspector, Glenn, Daryl and others on how to cut a miter with pro type results. And then get some scrap wood and practice on the scraps. Not hard but with a little practice you will get the hang of it.

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. It looks difficult, but don’t worry—with an $8 coping saw, a few special techniques and a little practice, you’ll be cutting perfect copes in no time.





There are few carpentry skills more rewarding than cutting and fitting a cope, but you’ll never know until you give it a try. So grab a coping saw and a chunk of molding and follow along as we show you step by step how to cope an inside corner.
A Simple Hand Tool Performs Magic
Copes are sawed with—you guessed it—a coping saw. You don’t need to spend a lot of money on one, however. The basic $8 version available at hardware stores, home centers and lumberyards works great. Pick up an assortment of blades. Use fine-tooth blades for thin material and intricate cuts. A blade with 20-teeth per inch works well for most copes. Some carpenters prefer to cut copes with a jigsaw. If you own a jigsaw, install a fine-tooth blade and give it a try.

A coping saw is designed to cut on the pull stroke (with the blade’s teeth facing the handle). But many carpenters, myself included, prefer to mount the blade with the teeth facing away from the handle so the saw cuts on the push stroke. Try it both ways and decide for yourself which method you prefer.

Cut a 45-Degree Bevel to Mark the Profile
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. shows you how to position a crown molding in your miter box to cut this bevel.

The Fine Blade Reaches the Tiniest Corners
The technique for starting the cope 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.

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. 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.

Crown and Cove Moldings Are a Little Trickier
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.

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

I wrote all this once but lost it when trying to post. so I found this, courtisy of:
How To Cope Tight Joints | Tools | Reader's Digest

Wow, Trimplus! Awesome first post!

Miters are definitley a tough skill to master. There are many tricks and tips that lots of us have compiled. Here are a few: Put a back bevel of 3 degres on the piece if it's and outside miter you want the 2 outside pieces to meet. Inside corners do the same but you want most of the wood to meet, depending on if you are caulking the top or if your doing built ups. The best thing you can do is visualize how it will look or imagine what will happen. Also cut test pieces say that you cut a test piece of 4 inches and the angles are correct and fit nicely, then all you need to do is minus the 4 inches of the overall length. Thanks and good luck.

The reason miters rarely work correctly in inside corners is due to the fact that they are usually not 90deg. You have the squares and you see this, the angle changes depending on where and how its measured. take a straight edge from corner out. You will see do to the way the drywall is finished you may have a build-up of mud in the corner and a dip out about a foot.

Bottom line. Its almost always best to cope inside. Thanks to trim plus you have a good starting point.

I just installed crown moulding. Had a heck of a time. Ending up over compensating the angles a degree or so to ensure a tight joint. Also cut test peices for every inside and outside corner. I stained mine so using caulk wouldn't work. Good Luck