Things You'll Need
Baseboard molding is fairly easy to cut and install, but because mitered angles are involved you have to be exact in your cuts if you want the molding to align. A miter box is designed to let you hand-saw a piece of wood using a pre-set angle. Miter boxes may have several available angles, but the outer angle will always be 45 degrees, which is the angle you need to cut your baseboard. When you cut baseboard for an outside corner, you need to cut both pieces to fit together. When you cut baseboard for an inside corner, the right side of the corner remains uncut, so you just have to cut the left side in your miter box and then cope the edge.
Place the baseboard that will go on the left side of the corner into the left side of the miter box, with the outside face of the baseboard resting up against the wall of the box that is closest to you. Align the spot on the baseboard where you want to start your cut with the rightmost gap in the box, but keep the majority of your baseboard on the left side of this slot. Secure the baseboard to the box, either using the built-in locking mechanism in the box, which is normally done by inserting dowels into holes in the bottom of the box, or by clamping the baseboard to the front wall of the box.
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Insert your backsaw into the rightmost slot in the closest side of the miter box. The tip of the saw should be lined up to the leftmost slot in the furthest side of the box.
Push down on the saw as you move it forward and backward, using long strokes. Continue to saw the wood until you have gone through the entire baseboard.
Remove the baseboard from the miter box and insert the baseboard that will make up the right side of the outside corner. Repeat the same process, except now use the leftmost slot in the miter box and have the baseboard extend out the right end of the box.
Place the piece of baseboard that will make up the left side of the inside corner into the miter box. Place the outside face of the baseboard against the inside face of the edge of the box that is closest to you. Align the spot you want to cut with the leftmost opening on the miter box, but keep the majority of your baseboard sticking out the left side of the box. Secure the baseboard to the miter box.
Insert your backsaw into the leftmost slot in the miter box, with the other end of the saw aligned with the rightmost slot in the other side of the box.
Saw back and forth, using long strokes, until you have cut through the baseboard.