Step by Step Instructions:
Step 1. Tape the template:
Position the template so it's in the center of the door. If you have a panel door, it should be a few inches above the door's bottom rail. If you have a door with a high bottom rail and and a small pet, you may want to use a different door.
On a flush door, keep the template about 4 inches above the door's bottom. Tape the template to the door. The bottom of the pet door should be parallel to the bottom of the door.
Step 2. Bore the corner holes:
Bore a 1/2-inch hole just inside each corner of the template so you'll have a starting point to insert your saw blade.
Step 3. Cut from hole to hole:
Use a jigsaw or keyhole saw to cut from hole to hole. After you cut three sides of the opening, apply duct tape across the cuts to support the scrap piece as you complete the cut.
Step 4. Mark the bolt holes:
Use a torpedo level or tape measure to position the frame, then tape it in place. Mark the holes with a pencil, then remove the frame and drill the bolt holes (one bit-size larger than the mounting bolts' diameter) through the door.
Step 5. Assemble the door:
Insert the mounting bolts though the inside frame, then the door, then the outside frame. Tighten all bolts finger-tight, then finish with an adjustable wrench. Saw off the excess bolt length with a hacksaw. Use a file or coarse sandpaper to remove any sharp burrs on the bolt ends.
If your pet resists using its new door, open the flap and tape it open. After a few days, lower the flap halfway. Gradually your pet will figure out that pushing the flap opens it.