Like most carpenters, I learned to cope trim the traditional
way, with a coping saw, a file, and sandpaper. But getting
tight fits for intricate oak trim took forever, so I switched
to a jigsaw fitted with the Collins Coping Foot (888/838-8988,
www.collinstool.com). This was faster, but I still had to use
sandpaper and files — especially on corners and tight
Then, two years ago, I saw a stair builder use an angle grinder
fitted with a sanding disk to scribe treads. I immediately
adopted his scribing technique and applied it to coping trim.
With the angle grinder, I could avoid using files except on
profiles with very tight radii. And after some experimentation,
I found that if I used a pneumatic die grinder along with the
angle grinder, I could quickly and accurately cope almost any
profile — even ones with tight radii — without
using sandpaper or files.
Tools and Supplies
When coping trim, it's best to use an angle grinder that runs
very smoothly. I use a 4 1/2-inch Metabo WE 14-125 Plus, a
solid, vibration-free model that allows me to grind with
precision. It's a powerful, durable tool that I use not only
for coping and scribing, but also for many rougher tasks.
Before you can cope, you must remove the guard from the grinder
and install a 4-inch or 4 1/2-inch sanding disk kit — a
$10 item at most hardware stores. If you're fortunate enough to
have two angle grinders, you can use two different grits of
paper — 24 grit for rapid stock removal and 50 grit for
finer work (see Figure 1). Otherwise, use just the 50-grit
paper; switching grits for each piece takes too much
Figure 1. Instead of switching disks, the
author switches grinders: He puts 24-grit paper on one tool and
uses it for fast stock removal, and 50-grit on the other for
precise finishing cuts (left). Curves too tight to grind with a
disk are cut with a die grinder equipped with a tapered carbide
carving burr or a cone-shaped metalworking burr
Die grinders consume a lot of air — much more than nail
guns — so be sure to use a small one that won't overwhelm
the compressor. I have an MSI-Pro 10029 gearless angle die
grinder, a light model that consumes about 4 cfm. Since that's
more than a small compressor can comfortably handle except in
short bursts, I use my 8-cfm wheelbarrow compressor if I have a
lot of coping to do. Even then, the compressor has to run a lot
to keep up.
Die grinders accept a variety of bits; I like to use a
fine-tooth Kutzall tungsten carbide wood-carving burr (Oliver
with a 1/4-inch shank. It has a long tapered head, which lets
me grind the trim's entire thickness even when I'm doing a
steep back cut.
Because grinders generate a lot of dust, I try to set up
outside — but I've also worked successfully in
well-ventilated indoor areas. Some people prefer to wear a
respirator when using these tools.
To begin, bevel the end of the stock with a miter saw, then
highlight the cut line by rubbing the edge of a pencil along it
(Figure 2). If the trim has a long, straight profile — as
some baseboard does — set the miter saw to a slight back
bevel and cut off the straight part. Remove as much material as
you can without going beyond the cut line.
Figure 2. Highlighting the cope line with
a pencil makes it easier to see.
Grinding the Cope
To cope the curved part, hold the piece face-up on a bench and
cut toward the cope line with a grinder. Always start with the
disk — or burr — in contact with the back of the
trim and then rock it forward toward the face. This makes for
better control because there's more resistance when you're
cutting through the entire thickness of the trim as you
approach the face.
With the coarse disk in place (if you're using one), rapidly
remove wood until you are close to — but not touching
— the pencil line (Figure 3). If there are any tight
curves — radii of less than 3/4 inch — notch them
out with the edge of the disk. Start at the deepest part of the
curve and work slowly toward the edges.
Figure 3. To prevent the disk from
catching an edge, the author starts grinding from the back and
then rolls the tool up toward the cope line (left). He uses
24-grit paper to get close (center), then finishes with 50-grit
paper, which leaves a smoother edge (right).
Up to this point, you can be pretty fast and loose with the
grinder without getting into trouble. Now, though, you want to
come right up to the line — so you need to be much more
careful and controlled. Switch to the finer grit disk and,
starting from the back, gently roll the spinning disk up toward
the face, tilting the grinder as necessary to follow the
contour of the cut line.
With complex profiles, be sure to pay attention to the entire
disk. It should contact the trim at a single point; if you
aren't careful, it may hit somewhere else and accidentally
remove material you didn't want to lose.
Tight curves. If the molding has sharp radii, use the
angled die grinder to carefully spin the narrow part of the
burr around the curve (Figure 4). I like to vary the speed of
the grinder: fast at first to rough out the bulk of the
material, and then slow for the delicate final cuts. Avoid
letting the burr contact too much of the arc at once; the
additional friction might cause it to catch and jump out of
Figure 4. The author uses a die-grinder to
cope the 180-degree curves on cap molding (above) and to
preserve the more delicate parts of a one-piece baseboard
(right). He copes the straight part of the baseboard by making
a stopped cut with a miter saw.
As you enlarge the curve, you can bring the burr up higher so
that the wider diameter part of it comes into contact with the
wood. You can also use the die grinder to touch up areas you
originally cut with the angle grinder.
Back cutting. Once the cope is cut to the line, it's
time to test-fit your work. With crown you usually need to do
some extreme back cutting to get the joint to fit. It's easier
to do this with a grinder than with a saw. If you hold the
grinder so the disk (or burr) is nearly parallel to the back of
the trim, you can remove a lot of wood from behind the face
without coming into contact with the coped line — thus
preserving the shape while getting rid of unwanted
I like to leave a little edge at the top of my baseboard or at
the bottom of crown and notch a triangle out of the noncoped
pieces. I do this to make it appear as though the joint were
mitered rather than butted together (Figure 5).
Figure 5. Normally the small projection at
the bottom of this crown (top left) would be cut off, but
instead the author makes a 45-degree notch in the edge of the
adjoining piece (top right). When the pieces are installed, the
cope fits perfectly and — viewed from below — looks
like a miter (bottom).
Die grinders are very good for coping hardwood trim, but they
work on other materials, too. When grinding soft material like
poplar, pine, and MDF, I switch from the fine Kutzall burr I
use for hardwoods to either a coarser Kutzall burr or a
standard solid carbide metalworkers' burr; the fine burr tends
to clog up and burn with softer woods.
Because I like to get as much use as possible out of my sanding
disks, they're usually so clogged and worn toward the end that
they burn the wood a bit. This isn't a problem for me because
the burn marks are on the back of the trim where no one can see
them — but the smoke can be irritating to breathe.
Using grinders to cope trim has required one alteration to my
normal habits: I drink a little less coffee on days when I'll
be coping, because the grinder technique works best with steady
hands. Also, this is one construction activity that I wouldn't
attempt without safety glasses and earplugs.Chris Kennel works for City Side
Remodeling in Denver.