A 45° miter joint is the perfect means for joining two pieces of molding in a 90° corner (such as case molding around a window). Unfortunately not all such corners are exactly 90 degrees, so the miter joint has to be adapted to fit tightly. Here’s how to go about it:
- Nail the top piece of molding in place with a 45° angle cut.
- Line up the side molding so it’s even with the frame and overlays the top molding.
- Mark the inside and outside points on the side molding where it intersects the top miter joint.
- Connect the two points with a straight line and make the cut along that line.
- The result should be a tight fitting miter that matches the existing corner.