Measure the bottom width and length of your air conditioning unit. Add three inches to both the width and length dimensions of the unit.
Mark both dimensions on the four by four foot piece of sheet metal. Shear the piece of sheet metal to length and width. Cut all four sides of the metal to make the finished cut piece square.
Set the combination square to one inch. Use the awl with the combination square to mark one inch on both sides of each corner of the sheet metal. Remove the four corners from the piece of sheet metal. Place the bulldog ships at the point where each one inch line contacts the edge of the sheet metal. Use the hammer to flatten the cuts at each of the corners you removed.
Place a center mark on one of the shorter width sides of the sheet metal. With the combination square extend the center mark from the edge of the sheet metal in three inches. Two inches in from the end that has the center mark, place a mark with the awl. Place the center punch on the location where the two inch mark and the centerline mark cross.
Insert the 1/8 inch to 1/2 inch step down bit into the drill. Place the tip of the drill bit on the mark left by the center punch. Run the drill bit through the sheet metal to create a 1/2 inch diameter hole. Clean the drilled hole on both sides with the grinder. Mark one inch in from the edge of the sheet metal on the centerline mark.
Set the piece of sheet metal into the sheet metal brake. Place one edge of the clamping die on the centerline mark on the width side of the sheet metal. Push the other end of the sheet metal into the brake the clamping die is aligned with a notched corner. Secure the sheet metal by locking the clamping die. Pull the bending die up slightly to create a five degree crease in the sheet metal. Unlock the clamping die. Align the other corner of the sheet metal with the clamping die, while holding the centerline mark in place. Perform another five degree crease from that corner.
Line-up and break the one inch flange on one of the long sides of the sheet metal. Spin the sheet metal and bend the one inch flange on the other long side of the sheet metal. Make the final two one inch bends on the box and pan brake.
Weld the corner of each flange. Smooth the corners with the grinder. Spray cold galvanizing onto each ground weld. Plug the 1/2 inch round condensate drain hole. Put water into the condensate pan to check the welds for leaks.