Cutting Coped Joints

Cutting Coped Joints, Saw along cut line with coping saw

Intro

Use coped joints instead of miters for an inside corner. You might have difficulty fitting inside miters because the wall surfaces tend to give slightly as you nail the pieces in place. Thus a miter joint that looks perfect when held up for a test fit is likely to gap when nailed in place. A coped joint, on the other hand, accommodates such variations.

A coped joint is essentially a butt joint in which one piece of molding runs right into the corner. The end of the adjoining piece is cut to match the profile of the first piece and butts up against it. This is not as difficult as it may sound; coped joints are much easier to cut than they look, and they are fairly forgiving of inaccuracies. The principal tool used is a coping saw.

Even the pros don't cut perfect copes every time. The trick is to take your time and leave the moldings a little long to begin with so you can sneak up on the perfect fit by fine-tuning the cut.

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Purchasing Molding by the Numbers

Each standard molding has a number (such as WM 51) assigned by the Moulding & Millwork Producers Association (MMPA). This number indicates a specific profile and its width. Some suppliers will provide you with a catalog of the moldings they stock, but for a comprehensive listing of all molding styles that are manufactured, you'll have to purchase a catalog from MMPA. There are currently two catalogs: one for softwood and another for hardwood.

When shopping, specify your moldings by the WM number rather than by a name such as "2-1/4-inch colonial casing," which might describe several different profiles.

As you calculate how much molding you need, don't simply measure the room and come up with a total number of linear feet. It is better to figure out how long of a piece you'll need for each wall and list the moldings that way. This minimizes the number of midwall splices you'll have to make. When listing the lengths needed, add a few extra inches onto each piece to allow for mistakes.

Even when you specify the molding by its WM number, two pieces of the same molding from different suppliers may not match exactly. If possible, select moldings from the same lot number so the profiles match at the joints.

Step 1

Start a coped joint by butting one of the pieces of molding into the corner and fastening it in place. When deciding which piece to cope, choose the one that will be least visible as you enter a room.

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Step 2

To reveal the line you will cope, miter-cut the end of the piece as though you were going to make an inside miter.

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The Line You Will Cope: Making the Line Clear

If the molding is prefinished, the profile cut line will show clearly when you make the miter cut. For unfinished molding, it can be helpful to run a pencil along the profile to help guide the cut.

Step 3

In a perfect world, a coped joint would be cut square to the surface (shown by the red line). In reality, a coped joint is undercut (black line) to accommodate any irregularities in the joint.

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Step 4

Saw along the cut line with a coping saw, angling the blade slightly to produce the undercut. Brace the molding on a bench or sawhorse. Clamping the molding is an even better idea.

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Step 5

Check the fit of the cope against the molding in the corner. If necessary, trim the piece with a utility knife.

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