Whether you're working with flat or crown, achieve a professional-looking joint that stays airtight season after season
When two pieces of trim meet at an inside corner, you could miter the joint, but most professional carpenters prefer to cope. An airtight coped joint is easier to produce: It doesn’t require the perfectly square corner that a mitered joint needs. A coped joint is also less likely to open up after a few seasons of expansion and contraction.
Although you need a miter saw for coping, the only specialty tools you need are a $10 coping saw and an assortment of blades. A 15-tooth coping-saw blade is the best all-around performer, especially for simple chair rails and baseboards. But you’ll want 18 teeth (or more) to negotiate the intricate cuts that crown molding requires.
When installing a new blade, make sure the teeth face forward (the same as a standard handsaw) and tighten the blade securely.
Flat molding is straightforward
Step 1: Miter cut determines the profile. Although you can trace the profile from one piece of trim to the other, a 45° inside miter cut achieves the same purpose. An efficient carpenter chops all the profiles for a particular room at the same time, then cuts each piece of trim to length later.
Step 2: Use a pencil to highlight the cutline. To make the profile of the molding more apparent, draw the flat edge of a pencil lead across the inside edge of the miter cut.
Step 3: Angle the cut inward. Start the cut with a few gentle pull strokes until the coping saw finds its groove; then switch to long push strokes.
Step 4: Angle the blade into the work so that the face of the cut becomes slightly proud of the back side. This slight angle is called a back bevel, or back cut.
Step 5: The back bevel allows minor adjustments to be accomplished using a few passes with a wood rasp rather than a belt sander.
Turn your jigsaw into a supercharged coping saw
If you measure your trim in miles rather than feet, you might want to invest $29 in the Collins Coping Foot (Collins Tool Company.; 888-838-8988; www.collinstool.com). The coping foot is simply a curved baseplate that substitutes for the standard, flat base found on a typical jigsaw. The manufacturer offers a coping foot to fit all commercially available jigsaws. Most install with the turn of a screw, though some saws require a shim to position the baseplate correctly.
With the coping foot in place, the saw is operated upside down, which takes a little practice but allows you to see the cutline perfectly. The curved base makes it easy to back-bevel a baseboard, but it was designed for quickly negotiating the intricate twists and turns that crown molding requires. Instructions for coping crown using a simple jig are included with the tool.
Crown molding takes patience and a steady hand
Step 1: Place the crown molding upside down in the miter saw and at an angle between the fence and base. Then make a 45° cut to reveal the profile for the cope.
Step 2: Crown needs a steep back bevel. Because it’s installed on an angle, unlike baseboard, crown molding must be coped with a significant back bevel, or the two faces won’t meet.
Step 3: It’s not easy to turn corners when sawing at such a steep angle, so the best strategy is to cut as far as you can from one end, back the blade out, and sneak up on the cut from another direction.
Step 4: Work inward from both edges to ensure that the last saw stroke separates the meaty center of the molding rather than the fragile outer edge.
Step 5: Close won’t do. If the cope doesn’t fit perfectly, a pencil serves to mark the high spots, which are removed easily with a rasp or some sandpaper.
Step 6: Fine-tune the curves. A medium-grit sanding sponge is particularly effective for shaping curved sections.
Photos by: Andy Engel