Tip 1: Cut plywood sheets on the floor with full support
I've cut a lot of plywood on sawhorses
with pretty good results, but when I want
really smooth finish cuts on an expensive
sheet, I always cut on the floor. That way
you're sure to get solid, stable support so
the plywood won't move, even if you
have to climb on top of it to complete
your cut. It also ensures that the cutoff
piece won't splinter, break or fall off as
you finish the cut.
Lay 2x4s under the plywood perpendicular
to the direction of the cut. The 2x4s
will be “sacrificed” just a bit when the
blade passes over them, but that won't
affect the quality of the cut. The system
works well for both rip cuts (parallel to
the grain) and crosscuts (perpendicular
to the grain). The more stable the plywood,
the better your chances for a perfectly
Tip 2: Set the blade depth to just clear the plywood thickness
Adjust the depth of your blade so that no
more than half a carbide tooth falls below
the bottom of the plywood (photo).
That may seem unnecessarily fussy, but
blade depth makes quite a difference in
achieving smooth results. This setting lets
the teeth shear the wood fiber rather than
chop it, and it helps stabilize the blade (less
vibration). Both factors minimize saw
tooth marks. The deeper you set your saw
blade, the more marks you get.
Set the saw along the plywood edge, lift
the guard and look closely as you set the
depth. It's also a good time to check the
blade for chipped or missing teeth. A
blade with bad teeth or wood pitch
buildup won't cut cleanly. Also note that a
circular saw cuts on the upstroke, which
often splinters the top edge (veneer)
slightly. The bottom edge usually remains
splinter-free. So always cut plywood with
the good side down.
Tip 3: Clamp on a solid straightedge for a guide
You can buy straightedges at home centers
and hardware stores, but for long cuts
I almost always use the “factory cut” edge
on a strip of 3/4-in. plywood. For one
thing, the factory edge is usually perfectly
straight (sight along the edge to make
sure). In addition, the 3/4-in. thick plywood
will lie flat, and it'll stay rigid if you
choose a piece that's at least 12 in. wide.
You only have to clamp the ends.
The tricky part is clamping it in the
right spot for an exact cut. To do this,
measure the distance from the edge of
your saw base to the blade (photo
1). Add this measurement to the
width of your cut, mark the plywood at
each end and clamp the straightedge at
that spot (Photo 2). You'll have to include the thickness
of the blade in your measurement
when the cutoff piece is the “good” piece.
Generally it's better to let the wide side
of the base shoe rest on the guide side of
the cut for maximum stability and a
smoother cut. That also allows the smaller
cutoff piece to move aside slightly as
you finish the cut, so you can finish the
cut cleanly, without binding.
Tip 4: Test the guide for accuracy before making the cut
Here's where you fine-tune the cut. Draw a fine pencil line about 2 in.
long marking the desired width of your piece. (We made a dark line for
photo clarity.) Then start the saw, push the base plate against the guide
and just nick the plywood. Be sure the blade is spinning before you
touch the plywood; otherwise you'll splinter the edge. Then measure to
the edge of the nick to double-check your measurements. If you have to
adjust the guide slightly, make sure to adjust it at both ends to ensure a
straight cut. Be fussy here. Retest until the guide is positioned just right.
Tip 5: Make the cut at a steady speed without stopping
Cutting speed depends on many factors, including the type and sharpness
of the blade and the type of plywood you're cutting. In general, a
sharp blade should flow through the wood with little force, as if it's
melting the wood away. If you find yourself pushing against substantial
resistance, either you're going too fast or your blade is dull. Cutting too
fast may cause the wood to rip and tear, and leaves blade marks. Going
too slowly may cause the blade to overheat and burn the wood.
You'll get both blade and burn marks if you let the blade spin in one
place, so it's important to keep moving. This is where working on the
floor pays off for long cuts. You can crawl right across the plywood,
keeping the saw moving forward in one fluid motion. And you don't
have to bend or stretch into an awkward position.
But the cord can do you in. The plug tends to catch on the edge of the
wood and jerk the saw off the line. Sometimes the saw even comes
unplugged. (I've had that happen more than once!) Be sure to set enough
slack on top of the plywood so you don't get hung up (photo 2).
Finally, be sure to keep the saw going all the way through the end of
Tip 6: Choose a blade with more teeth for smoother cuts
As long as they're sharp, any of these four 7-1/4-
in. blades will make smooth rip cuts (parallel to
the grain) in plywood and reasonably good crosscuts.
In general, the more teeth, the smoother the
cut. The disadvantage of the 140-tooth plywood
blade is that the teeth will dull much faster than
the teeth on the three carbide blades. This is especially
true if you cut particleboard. My favorite is
the 40-tooth carbide blade. I keep one in reserve
and use it only when I need a fine cut. However, if
you have a project that calls for a lot of fine cuts
in expensive plywood, don't hesitate to buy the
special 56-tooth laminate-cutting blade. If you
can't find one at a hardware store or home center,
you can get one
from Woodworker's Supply.
Tip 7: Tape crosscuts to reduce splintering
Crosscuts, that is, cuts perpendicular
to the grain, will splinter the top
veneer, even with a sharp blade. This
is a bigger issue when both sides of
the plywood will be visible. The best
solution is to buy an expensive laminate
blade (photo, above). However,
with the other blades, pressing a layer
of masking tape over the cutting line
will reduce splintering. Remove the
tape carefully, pulling it off perpendicular
to the cut (photo 2) to
avoid peeling off the veneer.
Tip: If you have to cut with the good
(finished) side up, reduce
potential scratches by taping
the bottom of the saw base
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Video: How to Cut Plywood
Spike Carlsen, an editor for The Family Handyman, will show you how to cut construction grade plywood and finish grade plywood with a circular saw. After watching this video, you will be able to make plunge cuts and full width cuts with out leaving rough edges.