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Fitting a countertop between two side walls and a back wall is one of the
most challenging installations you will ever face. Experienced cabinetmakers
can do this with ease by marking and scribing straight to the
countertop, but they have years of experience. I take a more roundabout
approach, but it’s virtually goof-proof.
I prefer to make a template of the opening and rout my top to match. This
prevents trimming too much from any side, which would create a gap that can’t
easily be repaired. I’ll show you a simple method for making this template
using a kitchen desktop that butts against a cabinet, a side wall and a back wall
as an example. I installed this desktop with no backsplash. If you intend to
install a backsplash, you don’t need a precise scribe on the back edge.
Materials
You’ll need a piece of plywood or MDF slightly smaller than the countertop
opening—about 1/4 in. less at each side and the back is sufficient. This board will be your template’s base and will rest
on top of the base cabinets or wall cleats.
You’ll also need three guide boards of
any 1/4-in.-thick material. Cut them
about 4 in. wide. Make two a couple inches
longer than the countertop’s depth
and one a few inches shorter than the
countertop’s width.
Make the template
Lay the template base on top of the
cabinets or cleats and temporarily secure
it with a couple of screws (Photo 1).
Position one guide board on either the
left or right end and push it up against
the side and back wall (Photo 2). Next,
you’ll need a washer whose rim is big
enough to span the widest gap between
the wall and the guide board. Put your
pencil tip in the washer’s hole and draw
a line on the guide board, letting the
washer follow the wall’s contour (Photo
3). Clamp the guide board to your workbench,
and use a belt sander to sand
down to the line (Photo 4). Check the fit
against the wall. When you’ve got a snug
fit, screw the guide board to the template
(Photo 5). Repeat the same steps on the
guide boards on the other side and on
the back. Cut the back guide board so it
fits between the two side guide boards.
Make a mark on the side guide boards
to indicate where you want the front
edge of the countertop to line up (Photo
6). Then, remove the template assembly
and set it on the countertop to be
trimmed. Line up the marks you made
with the front edge of the countertop,
and clamp the template in place (Photo
7). Note: Build your countertop about
3/8 in. larger in width and depth than
the opening.
Rout the top
Using a top-bearing pattern bit with a
cutting length at least 1-1/2 in. long,
trim around the template (Photo 8; see
Sources, below). Stop short of the
front left corner so you don’t blow it out,
and carefully finish the cut with a belt
sander (Photo 9).
Tilt the countertop into place (Photo
10). It should fit snugly, but if it’s too
tight, you may need to adjust the fit
slightly. To do this, reattach the template
slightly off center and rout the exposed
edge to gain a little clearance. If you follow
these steps carefully, you’ll end up
with a perfect fit.
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Click any image to view a larger version.
1. Three-wall scribes
are tricky because
both ends and the
back of the countertop
all have to fit snugly.
My technique
removes most of the
difficulty by starting
with a loose-fitting
template base. I’ll
scribe three guide
boards, one for each
wall, and screw them
to the template base.
2. Position the first
guide board on
the template base by
sliding it up against
both the side and
back wall. It must be
long enough to overhang
the front of the
template base by a
couple of inches.
3. Along the side
and back wall,
mark a scribe line
on the guide board
using a pencil and a
small washer. The
washer follows any
bumps or curves in
the wall. Repeat this
step with a second
guide board on the
other side.
4. Clamp the guide
board on your
workbench and carefully
sand to the pencil
line. When you’re
done, check the fit
against the wall. The
beauty of this
method is that if the
fit’s not quite right,
you can just mark
and sand again.
5. Screw the scribed side guide
boards to the template base.
Mark, sand and attach the back guide
board last, because it butts between
the two side guide boards.
6. Mark both side guide boards at
the exact point where you want
the front edge of the countertop
located. This mark will be used to
accurately align the guide boards on
the countertop.
7. Use a square to align the countertop’s
front edge with the marks on
the side guide boards. The countertop
must be slightly larger than the template
assembly.
8. Rout the countertop’s finished
shape using a topbearing
pattern bit. Start at the
countertop’s front right corner
and rout counterclockwise.
9. Stop routing short of the
front left corner and use a
belt sander to remove the
remaining material. This prevents
the router bit from chipping
out the front edge. A piece
of masking tape provides a clear
mark where to stop sanding.
10. Tilt the counter into place. Fasten it with screws from underneath through the
top of the base cabinet. A wood cleat screwed to the right-hand cabinet supports
this top on the right side.
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