By Michael “House” Tain
The result after a bore cut has been used to set up the hinge in a felling operation.
Start of a bore cut to set up the hinge in a felling application. Note angle of bar to start with “go” corner.
The bar inside of the wood continuing the bore cut now prevented from kickback by the slot that encloses it.
A bore cut being used on wood already on the ground to release pressure.
All photos by Michael “House” TainThe bore cut, also often called the plunge cut, is a chain saw cutting technique that, once understood and practiced, is an invaluable addition to tree care professionals’ mental toolboxes both aloft and at ground level. It may be used in a variety of ways including setting up the felling hinge of an upright tree while allowing additional time and safety, releasing tension or compression forces in downed wood in a controlled manner, or even simply saving energy while bucking up a log by allowing the operator to let the weight of the saw and their own body mechanics do the work. As valuable as the bore cut is, it is a technique that requires an intimate understanding and knowledge of the reactive forces of a chain saw; and is definitely not one that should be implemented into everyday work practices without some level of training and practice. Luckily, there are few tree care companies that do not have multiple pieces of large woody debris around their yard, thus allowing new learners the excellent opportunity to understand and practice the bore cut under controlled conditions. In addition, professional training organizations such as Arbor Canada Training and Education, ArborMaster, and North American Training Solutions all offer the opportunity to learn and practice the bore cut in their felling/cutting or chain saw courses. In any case, some level of training and practice coupled with basic principles can allow tree crews to start using the bore cut on a daily basis with safe profitable results.
The chain saw has four basic reactive forces which are typically described as push, pull, kickback corner, and starting corner. The kickback and starting corner can be even more simply described as “no” and “go.” The push force is the one experienced by the saw and operator when cutting with the top of the bar. As the chain is moving forward, away from the drive sprocket toward the tip of the bar, the saw tends to be “pushed” back into the operator. The pulling force is when cutting with the bottom of the bar, and the chain is moving back toward the drive sprocket, “pulling” the saw into the wood and away from an unwary operator. Although kickback has often been described as occurring at the tip of the bar, often with the instruction to not use the tip of the bar due to that danger, it more accurately occurs in the upper quadrant or corner of the tip. This is due to the fact that as the cutting tooth rolls over on its travels toward the bottom of the bar, the depth gauge is no longer properly setting up the cut, and the cutting tooth will take too big a bite and “grab” too much wood. This overly ambitious bite will cause the tooth to stop, and the resulting force will cause the saw to “kickback,” usually upward and backward depending on saw orientation. The lower corner or quadrant of the bar does not present the same problem; and if used properly, cannot kickback — thus giving it the name starting or “go” corner. Understanding and using these forces to operator advantage is a key component of bore cutting.
A bore or plunge cut must always be started with the lower quadrant/corner of the bar, to not do so will result in some form of kickback. As can be seen from the accompanying photographs, the cut is started with the bar at an angle to the wood being cut to ensure that only the starting or “go” corner is in contact with the tree or branch. As the tip of the bar bores into the tree, the operator slowly changes the orientation of the saw until the bar is going straight into the wood. Once a slot has been properly formed, though the operator may feel the saw jump and shimmy a bit as it goes into the wood, it cannot escape to kickback as it is contained within the slot. The intended purpose of the bore cut is going to designate where on the tree or piece of wood it is started, though it will, of course, always be started with the “go” corner. For example, when using a bore cut to set up the hinge in felling, and obviously when the tree is large enough to make it viable, the bore should be started well back from the face or felling notch. Starting too close means that the smallest mistake may have large consequences, such as cutting completely through the intended hinge. Starting further back will not only allow room for possible errors, but allow the luxury of correcting them with no, or very little, adverse effect. When using the bore cut to release tension or compression forces in downed wood, care should be taken to examine the tree or piece closely to determine where the forces are, and use ACTE’s valuable acronym CUT. Release compression wood first and tension wood last.
Once in or through the wood, cutting may proceed in the manner that is best suited for the situation. The top or bottom of the bar will both cut equally well in a properly maintained chain saw, thus operators should use whichever one allows them the safest and most comfortable operating position. In conditions or circumstances that call for precision cuts, where the bore cut needs to be as parallel as possible to an existing or intended cut, “heel and toe” cutting (in which the saw is rocked back and forth) should be avoided. Although, chain saws are meant to cut at full throttle, some “feathering” of the throttle is not only acceptable but desirable when cuts are getting close to one another, and precision is required, for once that wood fiber is removed it cannot be reinstalled.
The possible uses of the bore or plunge cut are many and varied; and there are few cases, once it is understood and practiced, that it cannot help but make felling and bucking safer and more efficient. Its use in felling allows the operator to set up a hinge of the desired thickness, leave an appropriately sized strap on the back of the tree, remove the saw and check the work area for clearance and safety, and then fell the tree by severing the strap, while also having the opportunity to quickly exit the danger zone around the base of the tree. The bore cut’s use in bucking up large wood on the ground under pressure also allows users the opportunity to set up all the cuts in a manner that will keep the wood in place, though all fibers are severed; and allow them to get safely out of the area prior to the wood being pulled or pushed apart.
The bore cut, besides some basic training and experience, does require a few things to work properly. A poorly maintained or poorly sharpened saw will, in all likelihood, not perform bore cutting well. In particular, saws in need of carburetor adjustment that “bog” or die when put in different positions will not be able to generate the chain speed needed to carry out a plunge cut. Chains on which operators have removed or excessively filed down all the depth gauges will certainly chatter or “bark” during bore cutting, making any degree of precision difficult. Non-professional chains, often called anti-kickback chains, with a large ramp in front of the cutting tooth, can make bore cutting a challenge.
These few basic principles provide a general introduction to the technique of bore or plunge cutting, a method that can be quite a help in the wide variety of situations and scenarios that tree crews find themselves confronted with on a daily basis. Once understood and practiced, this technique will hold a prominent place in any climbing arborist’s mental toolbox, helping them to get wood on the ground safely, efficiently, and with a measure of control they would not have had otherwise.
Michael “House” Tain is a contract climber, splicer, educator and writer associated with North American Training Solutions www.northamericantrainingsolutions.com and Arbor Canada Training and Education www.arborcanada.com. He is currently located in Lancaster, Ky., and can be reached via e-mail at email@example.com