The biggest problems one has when cutting plywood are:- the final inch of cut splintering
- the danger of saw kickback and resulting personal injury
All
of these problems can be avoided if you support the plywood so that as
the cut is made, the plywood does not fall or drop. Keep in mind that
as the circular saw blade moves its way through the wood, it cuts
safely and efficiently when there is minimal or no stress on the
spinning saw blade. A circular saw blade that gets pinched for any
reason becomes unsafe and can kick back resulting in serious personal
injury.
Saw-blade stress happens by default if you push the saw
blade too hard as you cut. But unnecessary and unwanted stress can
happen if the wood you are cutting starts to pinch the sides of the saw
blade. This side stress happens if the plywood sheet starts to drop or
fall as the blade cuts through the plywood.
Think of what
happens when you cut down a tree. After a notch is made to help guide
the fall of the tree, the saw starts to move through the wood. As the
tree falls, the gap at the notch gets smaller and the tree starts to
tear apart at the other side where the cut is not yet complete.
The
same thing happens on a smaller scale when improperly supported and/or
unsupported plywood is cut. As the saw cuts through the plywood one
part of the plywood is pulled to the ground by gravity. The gap along
the bottom of the cut line gets smaller and the top edge is stretched
and starts to tear apart the remaining wood that has yet to be cut.
This
bending motion of the wood pinches a spinning circular saw blade. If
the saw is still cutting while the plywood start to fall, the blade
gets pinched, it starts to make a whining sound and it is difficult to
continue the cut.
A basic way to support plywood while it is
being cut is to use four plastic garbage cans that have been turned
upside down. This makes the cans more stable. Space the cans so the
entire sheet of plywood is supported, and make sure the cans are not
under the saw-cut line. You may get better results using six cans with
three cans under the plywood on either side of the cut line. Six cans
are usually only necessary if you are cutting the plywood equally in
half either width or lengthwise.
Avoid using just a couple of
saw horses to support the plywood. As the cut is made, the piece of
plywood on each side of the cut line acts like a teeter totter and both
pieces of plywood may start to tilt. If this happens, the stress builds
on the blade.
For safe, trouble-free cuts, the plywood must be
supported in numerous locations so that as you cut it, the plywood does
not move up or down or left or right.