Does anyone know of a good way to trim hollow-core doors without damaging the edges of the cut?
This has always mystified me.
The secret is to use something that is more brissant,...like C-4 or plastique. Ammonium nitrate or dynamite just heave too much....
Use that blue painters tape and place right on the line you are cutting. Get a straight edge/level...score line with razor sharp utlity knife.
Between the tape and the scoring of the door , the door skin will not chip when you cut it.
http://www.woodmagazine.com/
The above magazine actually has a handful of nice woodworking tips.
Depending on how much you're wanting to trim, you might want to consider using a power plane or a router (clamp a straightedge to the door for a guide). These cut perpindicular to the face grain, so you don't have the problem with splintering at the blade exit.
Some of the problem with hollow core doors is the thickness of the veneer on the outer skins. One trick with solid ply pieces is to back-up the bottom side of the piece being cut so that the finished piece is actually sandwiched between the scrap. Most materials fail in shear at about 1/3 the force of static pressure, so when a saw blade tooth is pushing the material, if it doesn't have anything on the opposite side, it will tend to tear along the grains adjacen tto the cut being made. Saw teeth typically change from a cross cutting bit, to a digging bit to clear the cut material out of the way. The finer the teeth, then the finer the cut, although the slower the process and perhaps more heat generated in the cut.
The sandwiching tip is good for solid plywood, but on hollow core doors, there is typically a waffle core or generally hollow void beneath the skin. One can lessen the rough jagged cut by making a scored cut that doesn;t penetrate all the way through, then returning with a finer cut, but say with a jigsaw, the return cut from the blade, still pulls up on the veneer and the veneer can split.
Might try the tape method or scoring the exposed top then trimming with a plunge router so that the cutting is performed 90 degrees to the jigsaw cut pattern, but using the strength of the veneer to back up the cut,..i.e. a straight trimming router bit to make the cut.
If you are comfortable with a skil saw, just score right above the cut. Use a straight edge, and push the blade in as far as it will go. 1/8th inch if you can. That will stop the splintering which makes the edge look ragged.
If not, then use a hand held disk orbital sander with a course "40" grade sand paper. Use a face mask or have ample fluids to protect the throat!