Kickback causes many chainsaw accidents. Kickback can occur whenever the upper part (quadrant) of the tip of the guide bar has contact with, but does not cut through, an obstacle while the chain is moving. The chain is moving away from the operator at that point, so contact transfers the power to the bar, which quickly propels the guide bar upward and backward in an uncontrolled arc—often right toward the operator.
Kickback can happen with lightning speed. With a saw at full throttle, the chain can reach speeds upwards of seventy miles per hour. This speed, transformed to the saw’s rotation, means the tip of the bar can reach the operator in 15/100 of a second. No one can react that quickly and an accident is very likely to happen.
The chain brake was designed to prevent such accidents from happening. An inertial chain brake (sometimes called an “automatic chain brake”) can stop the chain in 6/100 of a second. A manual chain brake that must be pushed forward with the left hand can stop the chain in 11/100 of a second. It is easy to see the importance of these safety features.
Avoiding kickback
Most chainsaw accidents result from kickback: when the upper part of the guide bar tip—known as the kickback danger zone—contacts any solid object, the guide bar will jump back toward the operator.
Although some chainsaws have safety features to prevent kickback, handling the saw correctly is the best insurance. Always be aware of the guide bar tip’s location, and never cut with the tip. Watch for objects behind the one you are cutting; such hazards may be obscured by branches or leaves.
Three (staged) photos show how kickback happens:
After touching the upper tip of the guide bar, the kickback motion has started.
The downward motion of the chain around the saw nose starts the saw rotating clockwise.
The speeding chain may strike the operator in the head or shoulder. The saw in this photo is turned off.
Kickback occurs if there is an unexpected or sudden contact with wood in the upper quadrant of the bar nose.
This saw is liable to kick back when the upper part of the tip meets the wood.
Pay attention to where the bar nose is. The upper quadrant of the tip should not be touching the wood. And cut with full throttle in a slow, steady, controlled motion.
Kickback Danger Zone
If you stand directly in line with the guide bar, and your saw does kick back, you are almost guaranteeing an accident.
Always position yourself so you are not in line with the guide bar, as shown at left below. If the saw does kick back for whatever reason (center photo), it will bypass your head and shoulders (right).
Stand off slightly to the side of the cut.
A saw can kick back so quickly that you will not have time to react.
If you are standing to the side, the saw will bypass your head and shoulders. The saw in this photo is turned off.
Kickback can occur when the cutters of the chain bite too much wood and cannot cut it. Two things can cause this:
■ The depth gauges in the chain are too low, exposing too much cutter. (See the sharpening information in Chapter 6, here.)
■ The depth gauges are not rounded, causing them to bite.
■ Use a depth-setting gauge to file the depth gauges (see Chapter 6).
■ Round off the depth gauges.
■ Have your chainsaw sharpened by a professional.
Kickback can occur if you strike a branch that can move, a small twig, rock, or nail.
Cutting small branches that move when the saw hits them can cause kickback.
Do not cut small branches that can move unless you can reach the stable base of the branch where it meets the tree trunk.
Kickback is less likely if you trim small branches near the tree trunk.
Tip can contact trunk. Better to turn around and cut from other side, as shown above.
Avoid situations that can cause kickback:
Top or blade nose touches bottom or side of kerf during reinsertion
Blade nose strikes another object