How to Make a Window Frame

Set the trim on the wall next to the left side of the window. The long edge of the trim will be flush with the side of the window.

Move the trim so both ends protrude past the window edges. You want to have enough space on both ends of the trim to cut 45-degree angles. For example, if your trim is 4 inches wide, you want the trim to extend past both the top and bottom of the window by 4 inches.

Make pencil marks on the bottom and top of the trim where it meets the corners of the window.

Put on your safety goggles and gloves, and position the trim on the miter saw.

Cut the wood on a 45-degree angle with a miter saw, following your owner's manual for the proper instructions. The mark you made will be on the inside edge of the frame and the inside corner of the angle. Cut the 45-degree angle from the mark you made on the inside of the frame going out to the outside edge of the trim.

Cut the other end of the wood on a 45-degree angle in the opposite direction; this means changing the direction of the 45-degree angle on the miter saw. When the two cuts are done properly, the length between the top points of the wood are longer than the length between the inside points.

Sand the edges of the wood if they are rough.

Set the trim back in place on the left hand side of the window, and secure it in place with finishing nails and a hammer. Repeat steps 1 through 8 for the right side of the window.

Turn the trim for the top of the window upside down; this piece is called the header. The decorative side of the header should be facing you. Rest the header on the pointed ends of the trim previously put on the sides of the window. Turning the header upside down before marking it will ensure the that the miter cuts will meet properly inside the trim design when the frame is complete.

Make a pencil mark on the header. While the header rests on the trim points, you mark where the outside edge of the trim meets the header.

Turn the header so it is no longer upside down, and using the miter saw, cut the 45-degree angles on each end. The marks you made will become the outside points of the cut. Just like the side pieces of trim, the higher points on the outside of the header will be on the outside of the window frame.

Glue the ends of the header, and slide it between the two pieces of trim already in place. Nail it into place. Glue will help keep the joints together.

Wipe the excess glue off with a damp rag.

Repeat steps 9 to 13 to make the bottom of the window frame.

Fill the joints and nail holes with wood filler. Sand the filler when it is dry. See manufacturer's instructions for drying time.