How to Cap Window Trim With Aluminum Using a Brake

Lock a scrap piece of aluminum in the sheet metal brake. Mount the slitter on top of the brake. Cut the scrap piece of aluminum to determine the offset on your brake. Add the offset to the desired width of your drip cap. Clamp a sheet of aluminum into the brake and push the slitter along the rails, using one fluid motion, to cut the metal to the desired width.

Create the hem seam: Remove the slitter from the brake and insert the cut piece of aluminum into the brake. Lock it into place by pulling the top handle forward while lifting up the bending place as far as it will go. Use the clamp to compress the hem seam, creating a fold at the bottom of the metal. Finish the hem seam by flipping the piece, locking the seam into the brake and lifting the handle of the bending plate by 30 degrees. This creates the kickout.

Complete the drip cap profile: Insert the metal into the brake with the kickout facing upward and with about 1½ inches between it and the leading edge of the clamp. Lift the handle of the brake to an angle that matches the top of your window.

Repeat Step 3 with the middle fold of the drip cap facing down. Leave a space equivalent to the width of the space at the top of the window. Bend the cap to create an edge that will partially cover the window face. Create a second hem seam on the raw edge of the cap.

Place the drip cap: Use a pair of sheet metal snips to cut the drip cap to 1 inch wider than the top of the window header trim. Place the cap on the header trim and mark a small tab on the front and back where the cap meets the side trim. Snip away the front tab -- but make a slit at the back -- then bend the rear tab at a 90 degree angle to the rest of the cap.

Secure the drip cap: Fasten the cap using three 1¼-inch nails. Place one nail in the center and one on each end, about 1½ to 2 inches from the edge.