Sometimes, despite our best efforts, we end up with a gap in our half-lap joint.If the gap is small enough, particularly a hair-line gap, we can fix it during the finishing process with colored epoxy or a wax pencil. But sometimes the gap is significant, say three-thousandths of an inch, and we don’t want a solid line of filler present. In this instance, a wedge with the grain orientated correctly is warranted. Correct orientation of the wedge means aligning the wedge so it goes perpendicular to the grain of the appropriate rail or stile. If it is orientated with the grain, as your eye follows along the frame, you will see a slight bulge in the frame width at the joint.
Small wedges can be made by hand with a sharp chisel and a bench stop. For a consistent gap across the whole joint, I prefer to cut wedges on the table saw. Here’s how I cut and install them:
Step 1: Tilt the table saw blade over two degrees.
Step 2: Using a cross-cut sled with a stop, make a two-degree cut on the edge of a piece of your spare frame stock.
Step 3: Flip the stock over so the opposite face is now up in your cross-cut sled and adjust your stop to make a cut just under a 1/16”.
Step 4: Apply a light coat of glue to the wedge, insert it into the gap, and gently tap until firmly seated.
Step 5: Use a sharp chisel to trim it flush with the frame.
Sometimes a gap is wide enough to require a wedge repair, but it is not wide enough to be glued into place. You’ll know this is the situation if you apply glue to the wedge and the moisture (in the glue) causes the wedge to swell to the point that it is too big for insertion into gap. In this instance, I simply use a friction-wedge. A friction-wedge is just what it sounds like. I insert the dry wedge and gently push it in place with only the tension of the wedge in the gap holding it in place. CA glue can also be used in place of white or yellow glue, but beware, it will leave a dark glue line that may not be desirable on lighter wooden frames.