As any tree industry veteran knows, controlling a handheld internal combustion engine with any degree of precision and consistency is much more difficult than it looks to the casual observer.

One of the primary reasons for this is the reactive forces — or physics — generated by the chain saw itself. An understanding of these forces, and, even better, a knowledge of how to employ these forces to accomplish whatever “tree” task might be at hand, can help tree professionals be not only safer chain saw operators, but more efficient ones.

Once understood, the newly enlightened operator should take some time to practice his or her knowledge on scrap wood and cement into place the “muscle memory” required to control and employ chain saw reactive forces.

Push: Cutting with the top of the bar will generate a pushing force upon the saw and operator. Photo: Michael Tain

Pushing force

Though Salt-N-Pepa may have us think differently, pushing isn’t always “real good,” particularly if this chain saw reactive force takes the operator by surprise.

The pushing force affects both the chain saw and the operator when the top of the bar is employed to make a cut, or inadvertently comes into contact with the wood. The cutting teeth on the bar’s upper side are moving forward very rapidly toward its nose; should they be used to cut up into wood, or just come into contact, they are slowed with a corresponding force pushing the saw backward into the operator’s grasp and body. Operators in a strong, stable body position with both hands on the saw in the appropriate locations will absorb this “push” readily, although it can be quite powerful with larger chain saws.

“Appropriate locations” in this instance mean not only both hands on the saw, but right hand firmly on the rear handle controlling the throttle or “trigger,” and left hand grasping the top or side handle with thumb locked. Chain saw users not prepared to absorb the energy of this “push force” or not holding the saw correctly will quickly find themselves in a dangerous situation.

Pull: Cutting with the bottom of the bar will generate a pulling force upon the saw and operator. Photo: Michael Tain

Pulling force

Tree crew members do a lot of pulling through the course of their day, whether that is pulling lines up into trees, pulling cords to start motorized equipment, or even pulling the chain of a certain supervisor or fellow crew member to irritate them. However, the chain saw’s pulling force will instead pull an inattentive crew member.

This force is experienced by the saw and its operator when cutting with the bottom of the bar, the typical manner in which chain saws are used. At this point the cutter teeth discussed earlier in the pushing force have “turned the corner” at the tip of the bar and are moving rapidly back toward the saw. Any contact with the wood, intentional or otherwise, will “pull” the saw away from the operator and into the cut.

This close-up of the bar’s tip illustrates how the depth gauges affect the size of the bite the cutter tooth can make, generating the respective forces. Photo: Michael Tain

This “pull force” also is readily dealt with by operators in a strong, stable body position with appropriate hand location, but users unprepared for this “pull” will quickly find themselves in a dangerous situation. Once again, both hands should be in those “appropriate” positions to control the force.

Chain saw operators aloft should always keep in mind both the pulling and pushing forces, as the respective movement may very quickly move them from a stable cutting position to one that’s unstable, and dangerous.

No corner

While many new chain saw-users are often told that using the tip of the bar causes kickback. This is only partially true, and, in short, an unfair indictment of a very useful part of the chain saw bar.

Kickback occurs when the saw’s bar is thrown backward and upward toward the operator at high speed and with great violence, and it is certainly extremely dangerous. In reality, although kickback does occur at the tip of the bar, it is only possible at the upper quadrant of the tip, commonly called the kickback or “no” corner.

Looking closely at how the cutter teeth “turn the corner” at the nose of the bar illuminates how the violent chain saw reactive force of kickback — and how to avoid it. The cutter tooth’s depth gauge, also called a drag or raker, “sets up” how large a bite of wood the cutting surface takes. As the tooth turns downward through the upper quadrant, the depth gauge goes first, allowing the tooth to take way too big a bite to swallow.

A close-up of the bar’s tip, diagramming its “no” and “go” quadrants. Photo: Michael Tain

The saw experiences a violent reaction, stopping the cutter tooth for just a fraction of time and transferring that energy or force into a movement that “kicks” the saw and bar “back” toward the operator. This is described as a rotational kickback, in which the chain saw rotates upward and backward toward the user.

A different type of kickback can occur when the bar of the saw is “pinched” between the two surfaces of wood being cut. This pinching causes the saw to “push” back toward the user, at which time the “no” corner can hit the wood and create rotational kickback.

Operators must always be aware of the bar’s “no” or kickback corner, and do their best to avoid contact with material.

Go corner

While the upper quadrant of the nose of the bar should be avoided at all times, the lower quadrant can be very useful. In the first place, this area holds no potential for kickback as can readily be seen by examining the actions of the cutter teeth again.

As the tooth turns under the center tip of the bar, the depth gauge or raker goes down first, thereby eliminating the possibility of the cutter tooth getting too much of a bite, or, really, a very large bite at all. This design feature can be used for any number of advanced cutting techniques, such a plunge or bore cutting, and is particularly useful in advanced felling/cutting methods, such as key notches.

Read more: Proper Chain Saw Techniques

An illustration of using the lower quadrant of the bar’s tip, or the “go” corner, to start a bore or plunge cut. Photo: Michael Tain

For this reason, along with its use in beginning bore or plunge cuts, the lower quadrant of the bar’s tip is commonly called the starting or “go” corner.

While bore or plunge cutting would require much more detail to explain completely, the starting point is the lower quadrant of the tip of the bar in which a slot is formed into which the saw is then slowly, and with control, rotated.

A key notch, one of the advanced cutting techniques in which the use of the bar’s tip, along with understanding chain saw reactive forces, is imperative. Photo: Michael Tain

This method fairly effectively eliminates the possibility of kickback and allows the operator to remain stable while cutting through the heart of a tree or log.

Editor’s note: This article was originally published in Tree Services in April 2015 and has been updated for accuracy and comprehensiveness.