Q: I am replacing an interior door that needs to be cut down. Either I
bought the wrong size door or the opening for it is not a standard size.
The door is hollow and I need to cut it down by about an inch in height
and one-quarter in width. What is the best way to do this, and does it
severely weaken the door?
A: If you bought your door from a home center, chances are you will have
to trim it for width.
You say you need to cut "one inch" off the height? That sounds excessive.
My guess is that the opening may not be standard or maybe the height of
your flooring is taller than most.
Anyway, cutting the door is not big deal; you just can't cut too much off
of it.
Let's face it, a hollow core door is a cheap door. If you were to peel the
veneer off of one, you would see a wood frame around the perimeter of the
door (there is some additional wood around the hole for the doorknob). To
support the veneer sides inside of the wood perimeter are cardboard
supports that wander throught the door. This explains why hollow core
doors are so light and inexpensive, as well as being inexpensive.
Needless to say, since you are working with only one frame of wood to
trim, you have to be careful about how much to cut. The amount you need to
cut from your door is fine with a few caveats.
When cutting the width of the door, cut it on the hinge side. If you cut
material away from the doorknob side, it will change the backset (the
distance from the doorknob to the edge). If that happens, the doorknob
latch will be exposed, it won't fit correctly, and then you'll have to buy
a new door. So cut your sliver from the hinge side, but make it clean,
square and thin.
A tablesaw is ideal for this, but a circular saw will also work. If you're
using a circular saw, clamp the door to the work surface and make sure the
blade is set to 90 degrees. If you have even the slightest bevel on the
hinge side, when you mount the door, you will put stress on the hinges. In
turn, that puts stress on the now-thinned-out frame and you will have
problems.
Use a straightedge and clamp it to the door. Finally, run a piece of tape
along the area where the blade will cut. This will help prevent tear-out,
as the blade comes up through the door.
If you take too much material from the hinge side, the screws that secure
the hinge to the door won't have enough wood to bite into. That could take
away the needed support for the weight of the door. The long and short of
it is that if you need to cut a good amount of wood from the width of the
door, you may need to order a custom-size door. Expect to pay double and
wait 7-10 days to get it.
Cutting the height of the door is not nearly as risky. Generally, a door
gets cut on the bottom due to the tall carpeting that may rub on it. But
take a few measurements before you cut. If you door has a pre-cut hole for
the knob, make sure it is going to line up with the stike plate on the
jamb. If it doesn't, you may consider taking a little off the top as well.
You can cut the height of the door in the same manner as the width
described above.
If you have a significant amount to cut, you are going to cut beyond the
frame and into the hollow of the door. This is fine, but you should
replace the frame piece back into the hollow to strengthen it. You will
have to chop the veneer from both sides of the frame to get it to fit back
into the hollow.
Use a chisel and a hammer and cut the veneer away. You may have to sand
the frame piece to get it to slide smoothly back into place. Slather the
frame piece with wood glue and slide it into the hollow area and wipe away
the excess glue before it dries. Then clamp it together until it dries.
The only thing left now is to hang the door. Line up the hinges and cut
out the mortises for the hinges (the hinges lay in the mortise so the
entire edge is flat). Mark lines for the hinges and chop out the area
using the hammer and chisel (or you can buy a template and bit). Pre-drill
holes for the hinge screws and screw the hinges to the door and then the
jamb. Remember, don't crank the screws completely tight until you are
happy with the overall fit of the door.