Felling a tree is not simply cutting through the trunk. It is a precise geometric operation that uses a “hinge” of wood to steer thousands of pounds of falling mass. Understanding notch mechanics, hinge function, and back cut positioning separates controlled removal from catastrophic accidents.
The physics is unforgiving. Mistakes measured in inches result in failures measured in property damage and injuries.
Assessing Lean and Hazards
Before the saw starts, fellers must analyze multiple factors.
Side Lean determines whether the tree naturally pulls left or right of the intended target. Even slight side lean can redirect falls significantly over the height of a tall tree.
Forward/Back Lean indicates whether the tree will sit back on the saw during cutting. Back-leaning trees require wedging or rope assistance to fall in the intended direction.
Center of Gravity location depends on canopy distribution. Heavy branches on one side shift the center of gravity away from the trunk centerline, affecting fall direction.
Escape Path Planning must be completed before any cutting begins. The escape route runs 45 degrees diagonally away from the fall line, providing maximum distance from both the falling trunk and potential “butt kick” (trunk jumping backward off the stump).
The Notch: Face Cut Geometry
The notch determines fall direction. Three configurations serve different purposes.
Conventional Notch (45°) angles the top cut downward while keeping the bottom cut flat. The tree falls until the notch closes at 45 degrees, at which point the hinge breaks. This can cause loss of control before the tree reaches the ground.
Open Face Notch (90°) uses one cut angled down at 50 degrees and another angled up at 40 degrees. This large opening allows the tree to fall completely to the ground without the notch closing. The tree remains attached to the hinge (and under control) for the entire descent. This is the modern safety standard.
Humboldt Notch takes the wedge from the stump side rather than the log side. Loggers use this to preserve valuable timber length. The mechanics otherwise resemble conventional notching.
| Notch Type | Angle | Hinge Release | Best Application |
|---|---|---|---|
| Conventional | 45° | Before ground contact | Quick removal, low-value |
| Open Face | 90° | At ground contact | Maximum control, residential |
| Humboldt | 45° | Before ground contact | Timber harvest |
The Hinge: The Most Critical Component
The uncut strip of wood between notch and back cut forms the hinge. This component determines whether felling is controlled or chaotic.
Function mimics a door hinge. The fibers guide the tree’s fall direction and prevent twisting or sideways movement during descent. A proper hinge keeps the tree attached and steerable until it reaches the ground.
Dimension Rules establish that hinge thickness should equal approximately 10% of the tree’s DBH (Diameter at Breast Height). A 20-inch tree requires a 2-inch thick hinge. Hinge length should span approximately 80% of the tree’s diameter.
Failure Modes result from hinges that are too thin (break immediately, losing all steering), too thick (prevent the tree from falling), uneven (cause twisting), or cut through entirely (eliminate all control).
The Back Cut
This final cut from the opposite side of the notch releases the tree.
Positioning places the back cut level with or slightly above the apex (innermost point) of the notch. Cutting below the notch apex allows the tree to slide backward off the stump.
Hinge Preservation requires stopping the back cut before reaching the hinge. The gap between back cut and notch defines hinge thickness. Cutting through the hinge creates a “barber chair” (vertical splitting) or uncontrolled fall.
Wedging provides mechanical assistance for back-leaning trees. Plastic or aluminum wedges are driven into the back cut behind the saw. Pounding wedges with a sledge lifts the tree’s center of gravity past the pivot point, forcing it to fall against natural lean.
Bore Cutting: Advanced Technique
For leaning trees or species prone to splitting, the bore cut (plunge cut) provides safer alternatives.
The Technique follows a specific sequence:
- Cut the notch as normal
- Plunge the saw tip through the tree behind where the hinge will be
- Cut backward and sideways to establish exact hinge dimensions
- Leave a “strap” of holding wood at the back of the tree
- Remove the saw, verify the drop zone
- Cut the strap to release the tree
Advantages prevent barber chair failures because the hinge is fully established before the tree is free to move. The holding strap provides final control over release timing.
Barber Chair: The Fatal Failure
Barber chair occurs when the trunk splits vertically during cutting, creating an explosive upward thrust of wood. The term references old-style barber chairs with footrests that snapped upward.
Causes include cutting trees under heavy side or forward lean without proper technique, cutting back-leaning trees without wedges, and species with straight grain (particularly Pines) that split easily along their length.
Prevention requires proper notch depth (typically 1/4 to 1/3 of trunk diameter), bore cutting for leaning or high-risk species, and never rushing back cuts on stressed trees.
Common Felling Mistakes
Several errors produce most failures.
Shallow Notch (less than 1/4 diameter) doesn’t create sufficient space for controlled hinge release. The notch closes before the tree reaches the ground, breaking the hinge early.
Back Cut Too Low allows the trunk to slide off the stump backward, potentially into the feller’s escape path.
Back Cut Too Deep severs the hinge, eliminating all directional control.
Ignoring Lean and attempting to fell against natural weight distribution exceeds the hinge’s steering capability.
No Escape Path leaves nowhere to go when the tree begins moving.
The physics of felling remain constant. Trees fall according to leverage, gravity, and wood mechanics. Every safe fell follows the same principles. Every accident deviates from them.
Sources:
- Notch mechanics: OSHA logging safety guidelines
- Hinge dimension standards: Forest Service felling protocols
- Bore cut technique: Game of Logging professional training curriculum
- Barber chair analysis: Tree Care Industry Association accident investigations