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From the pages of Fine
Woodworking Magazine
Tablesaw Kickback
Many have
experienced it, but few know why it happens
by Lon Schleining
On the
first day of class I ask my woodworking students if they've had a kickback
on the tablesaw. I always get a fair number of hands in the air, but few
of the students can tell me what happened. And often those who have had
the unsettling experience of carving a nice, deep furrow in a piece of
wood and having it fly across the shop don't usually know what caused it.
It all happens so fast that it's over by the time they realize it's
occurred.
Before I let my students get
near a tablesaw, I do a little dog-and-pony show to demonstrate the
dangers of kickback. Using styrofoam to represent a piece of plywood, I
show how the cut should be made and then what occurs if the piece drifts
away from the rip fence. Crouching out of the flight path, I simply let go
of the piece for a second, and off it goes.
A kickback occurs when the leading corner of a piece being
cut rotates away from the rip fence. The piece then gets caught up between
the back of the blade and the fence. As the back of the blade -- the part
that cuts upward--begins to gnaw into the freshly cut edge of the piece,
the piece quickly rotates, getting caught diagonally between the fence and
the blade. The corner of the piece closest to the operator and against the
rip fence is the pivot point around which a radius cut is made. The piece
then acts like a pole-vaulter. Rotating further and moving faster now, the
piece rides up and over the blade and is hurtled into the air to the left
side of the blade. If you're lucky, it will fly over your left shoulder.
If you're not lucky, a board with a few horsepower of force behind it will
hit you. This is also why it is such a bad idea to stand to the left of
the operator and watch him work.
Afterward, you'll usually spot a crescent-shaped cut on
the bottom of the piece. This crescent cut is the result of the piece
rotating as it crosses over the top of the blade. It's as if you drew a
circle with a compass, putting the center point at the corner closest to
the operator and against the fence.
Certain types of cuts are more prone to kickback than
others. A square piece being trimmed is the most likely to cause trouble,
because any drift away from the fence will cause the piece to bind. Any
piece cut against the rip fence that is either square or rectangular (with
a width approaching at least half or more of its length) is a very
hazardous cut. Typically troublesome pieces are drawer bottoms and small
parts.
But if the piece is kept solidly against the rip fence and
pushed all the way through the cut and beyond the blade, it's unlikely
that a kickback will occur. Keep your eyes on the rip fence just past the
blade to make sure the piece is firmly in contact with the fence
throughout the cut. The critical time is often just after the front of the
blade has cut all the way through the piece. The waste lies on the table
rattling against the blade, distracting you from the very real task of
keeping the piece firmly against the rip fence until it is well past the
blade. A moment's inattention and ...
After the class understands
the danger of kickback, I repeat the operation with the splitter and blade
guard in place. When I let go this time, nothing happens. Then I use a
push stick to force the piece away from the rip fence and into the blade.
Again, nothing happens. This is because the splitter prevents the rotation
of the piece away from the fence.
Lon
Schleining teaches woodworking and builds custom stairs in Long Beach,
Calif.
Photos: Joe Romero; drawing: Vince Babak
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and more accurate
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