I’m replacing my trim around the windows and doors and also replacing the baseboard. What is the secret in getting good fits in both places? -Raymond
In a perfect world, all corners would be square, floors level, walls plumb, and lumber straight. Unfortunately, that is seldom the case. Like any good illusionist, a trim carpenter knows that it’s what you see that matters most. Often it’s better to leave a slight gap on the backside of a joint than attempt a perfect fit. This is particularly true of coped joints, where the back of the joint is cut away with only the front edge of the molding touching.
To install trim you’ll need a good miter saw with a quality blade, some thin strips of wood to act as fence shims, a block plane, a utility knife, and a coping saw. Start by making a few test cuts to fine-tune the angles and vertical alignment of your miter saw.
For window and door casings, miter one of the side pieces and the matching end of the top piece, checking to see if they fit tightly together when aligned to the frame. Minor adjustments can be made with a sharp block plane set to take a very thin shaving. Always plane with the grain of the miter joint, from the short edge to the long.
Larger adjustments are made by recutting the joint slightly on the miter saw using a thin shim of wood held against the fence. Position the shim near the blade end of the fence if the gap in the joint is on the short inner side of the miter, and toward the far end of the fence if the gap is on the long outer end. After you have a good fit on one side of the casing, repeat the process for the other end.
Baseboards have miter cuts on outside corners and coping cuts on inside corners. Fit the longer runs first, that way any scraps can be used for shorter sections. Work from the inside corners out, installing wall to wall pieces first and saving those broken by doorways or outside corners until last.
If there’s a gap on the straight cut of a coped joint, hold it in place and trace a line the width of the gap along the joint then trim to it. After the baseboards have been installed, gently tap along the sharp edge of outside miter joints with a hammer to round them over slightly and hide any gaps.