Kickback
When the saw blade becomes pinched or twisted in the cut, kickback
can occur. The saw is thrust rapidly back toward the operator. When
the blade is pinched or bound tightly by the kerf closing down, the
blade stalls and the motor reaction drives the unit backward. When
the blade becomes twisted or misaligned in the cut, the teeth at the
back edge of the blade can dig into the top surface of the wood
causing the blade to climb out of the kerf and jump back toward the
operator.
Kickback is more likely to occur when any of the following conditions
exist.
1. IMPROPER WORKPIECE SUPPORT
A. Sagging or improper lifting of the cut off piece causing
pinching of the blade.
B. Cutting through material supported at the outer ends only
(see Figure 17). As the material weakens it sags, closing
down the kerf and pinching the blade.
C. Cutting off a cantilevered or overhanging piece of material
from the bottom up in a vertical direction. The falling cut off
piece can pinch the blade.
D. Cutting off long narrow strips (as in ripping). The cut off strip
can sag or twist closing the kerf and pinching the blade.
E. Snagging the lower guard on a surface below the material
being cut momentarily reducing operator control. The saw can
lift partially out of the cut increasing the chance of blade twist.
2. IMPROPER DEPTH OF CUT SETTING ON SAW
Using the saw with an excessive depth of cut setting increases
loading on the unit and susceptibility to twisting of the blade in
the kerf. It also increases the surface area of the blade avaliable
for pinching under conditions of kerf close down.
3. BLADE TWISTING (MISALIGNMENT IN CUT)
A. Pushing harder to cut through a knot, a nail, or a hard grain
area can cause the blade to twist.
B. Trying to turn the saw in the cut (trying to get back on the
marked line) can cause blade twist.
C. Extended reach or operating saw with poor body control (out
of balance), can result in twisting the blade.
D. Changing hand grip or body position while cutting can result
in blade twist.
E. Backing unit up to clear blade can lead to twist if not done
carefully.
4. MATERIALS THAT REQUIRE EXTRA ATTENTION
A. Wet lumber
B. Green lumber (material freshly cut or not kiln dried)
C. Pressure treated lumber (material treated with preservatives
or anti-rot chemicals)
5. USE OF DULL OR DIRTY BLADES
Dull blades cause increased loading of the saw. To
compensate, an operator will usually push harder which further
loads the unit and promotes twisting of the blade in the kerf.
Worn blades may also have insufficient body clearance which
increases the chance of binding and increased loading.
6. LIFTING THE SAW WHEN MAKING BEVEL CUTS
Bevel cuts require special operator attention to proper cutting
techniques – especially guidance of the saw. Both blade angle
to the shoe and greater blade surface in the material increase
the chance for binding and misalignment (twist) to occur.
7. RESTARTING A CUT WITH THE BLADE TEETH JAMMED
AGAINST THE MATERIAL
The saw should be brought up to full operating speed before
starting a cut or restarting a cut after the unit has been stopped
with the blade in the kerf. Failure to do so can cause stalling
and kickback.
Any other conditions which could result in pinching, binding, twisting,
or misalignment of the blade could cause kickback. Refer to the
sections on “Adjustments And Set-Up” and “Operation” for
procedures and techniques that will minimize the occurrence of
kickback.
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