To cut off a door without splintering the finish, use a guide and sharp blade in a circular saw, and deeply score the cut line with a utility knife.
Put a sharp blade in your circular saw, score the cut line and clamp on a straight edge for a guide.
Set the guide so that you cut slightly to the waste side of the scored cutting line. Lightly bevel the finished edges with sandpaper.
If you’ve just installed carpeting, your doors will probably rub and bind, which means that you have to trim off the bottoms. Trimming a wood door with a circular saw without splintering the wood or damaging the finish is a challenge. Here’s the method that works best for me.
First mark the clearance needed on the door. Then pull out the hinge pins and lay the door on padded sawhorses.
Mark the cutting line on the top face and edges of the door and apply a 6-in. wide strip of masking tape along the line to protect the door’s finish from the circular saw’s base plate.
Next, score the cutting lines 1/16 in. deep with a utility knife. I like to clamp a metal straightedge to the door on top of the masking tape along the cutting line. This helps to guide the knife, and then if the knife slips, it only scars the waste side of the cut. You don’t need to score the underside of the door.
Make sure your saw blade is sharp and has a minimum of 18 teeth. Hold the circular saw against the edge of the door as if you’re ready to cut. With the blade teeth held just to the waste side of the scored line, mark the masking tape along the opposite edge of the base plate.
Position a straight saw guide at this mark, parallel to the cutting line, and clamp it at both ends. A 3/4-in. thick guide is thin enough to provide clearance under the saw’s motor.
Hold the saw against the cutting guide and check the position of the blade’s teeth. They should be just outside of the scored cutting line. Make the cut slowly. The scored line will stop the splintering. The bottom side of the door won’t splinter because the saw teeth cut up into the wood.
Lightly sand all the edges along the new door bottom to soften them, then rehang the door.