The process of safely and efficiently cutting a felled tree trunk into manageable segments is known as “bucking.” This differs significantly from “felling,” which is the act of cutting down a standing tree. Bucking presents its own distinct set of hazards, primarily related to the unpredictable movement of the log when internal wood stresses are released. Understanding the forces at play and adhering to strict procedures is paramount to avoiding dangerous situations like chainsaw kickback, saw binding, and log rolling.
Essential Safety Gear and Work Area Preparation
Before approaching any log, proper personal protective equipment (PPE) is essential. Head protection must include an ANSI Z89.1-rated helmet, often integrated with a face shield and hearing protection to guard against flying debris and sustained noise levels. Leg protection is mandatory, requiring chainsaw chaps or pants constructed with interwoven layers of cut-resistant material designed to stop a moving chain upon contact.
Footwear should consist of steel-toed, high-top boots to protect against dropped logs and provide ankle support on uneven terrain. Wear cut-resistant gloves that balance protection with the necessary dexterity to operate the saw controls. Preparing the work area involves clearing all surrounding brush, debris, and potential trip hazards to establish clear, unobstructed escape routes.
The log must be stabilized before any cut is initiated. Use cribbing—short lengths of lumber or small logs—to elevate the trunk slightly off the ground, which prevents the saw chain from striking dirt and dulling. Ensuring the log cannot roll is important, and you should always begin cutting from a position that allows rapid movement away from the log’s path should it shift.
Identifying Trunk Stress: Tension and Compression
The challenge in bucking is managing the internal forces of tension and compression, created by the log’s weight and support. Tension occurs where wood fibers are stretched, causing the kerf (the slot created by the saw) to open when cut. Conversely, compression occurs where fibers are squeezed together, causing the kerf to close and pinch the saw bar.
A simple visual assessment of the log’s support points is the first step in determining these forces. If a log is resting on the ground but is only supported at its ends, the middle section will sag. In this common scenario, the top surface of the log is under compression, while the bottom surface is under tension. If a log is cantilevered—supported at one end but hanging free at the other—the forces reverse: the top is under tension, and the bottom is under compression.
Identifying the compression side is important because cutting there first will immediately bind the saw bar, potentially leading to kickback or trapping the saw. A tension area can be confirmed visually where the log appears bowed outward, or by watching the kerf; if it begins to open as you cut, you are in a tension zone. The goal is to cut in a sequence that releases tension or prevents compression from pinching the saw.
Execution: Step-by-Step Bucking Techniques
The correct cutting sequence depends entirely on the stress analysis of the log. The general principle is to always cut the compression side first and finish on the tension side. This procedure prevents the weight of the log from closing the cut and trapping the saw blade.
When the log is supported only at its ends (compression on top, tension on the bottom), the technique is a two-part cut known as “underbucking.” First, make a cut from the top, or “overbuck,” going about one-third of the way through the diameter. Then, finish the cut from the underside, or “underbuck,” aligning the second cut to meet the first. The initial top cut prevents the log from splitting when tension is released, and the final upward cut releases the tension without pinching the bar.
For logs supported along their entire length or free-hanging at one end (tension on top, compression on the bottom), the technique is “overbucking.” Make a partial cut from the bottom, approximately one-third of the way up, and then complete the cut from the top.
Using Wedges for Stress Management
In situations where the log is too large or the stress is uncertain, use a plastic bucking wedge. The wedge is inserted into the kerf of the top cut as the cut deepens and is tapped in with a non-metallic tool to keep the cut open, counteracting compressive forces. This allows the sawyer to complete the cut from the top without the bar binding. This method is also effective for logs resting directly on the ground; a bore cut creates a notch, allowing a wedge to lift the log slightly and prevent the saw tip from hitting the dirt on the final pass.
Selecting and Maintaining the Right Tools
The chainsaw is the tool for bucking, and selecting the correct guide bar length is important for efficiency and safety. The bar should generally be at least two inches longer than the diameter of the wood you plan to cut most often. For very large trunks, a bar that is double the diameter is often necessary, requiring the log to be cut from both sides.
Several accessories streamline the bucking process. Plastic felling or bucking wedges are necessary for safely managing wood stress and preventing saw binding. A cant hook or peavey is useful for rolling and repositioning large logs, reducing the need for awkward cuts and keeping the saw chain out of the dirt.
Consistent maintenance ensures the saw operates safely and effectively. A dull chain requires excessive force, increases the risk of kickback, and slows the cutting process. The saw chain should be sharpened regularly, and the chain tension must be checked frequently to prevent derailing. Use the correct fuel-to-oil mixture for your two-stroke engine to ensure proper lubrication and a long service life.