The Notch: How Angle Affects Function

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The safe and controlled removal of trees by arborists in urban settings, requires a fundamental understanding of the notch and how it functions. Whether you’re removing a treetop, rigging, or felling an entire tree, the notch is central to achieving safe and predictable results. This skill requires both knowledge and experience, allowing professionals to maximize safety, control, and precision on every cut.

What Is a Notch?

A notch is an opening cut into a piece of wood that creates an angle. Technically, this opening is known as an aperture.

There are many types of notches, but the three most common in tree work are:

• Humboldt

• Conventional

• Open-face notch

  
  

Despite their variations, all notches create an angle between two cuts: the top kerf and the bottom kerf. Where these two cuts meet is called the apex of the notch.

Cutting the Notch

During a felling operation, an operator may choose to cut:

1. The top kerf first

2. Then the bottom kerf

This is because looking through the kerf provides a clear sight window, helping the operator avoid by-passing the apex and enabling precise alignment using the chainsaw’s sight lines. This visual guide is essential for aiming the tree in the intended direction of fall.

A good rule of thumb: The apex should be approximately 80% of the tree’s diameter. This ensures your hinge has a greater likelihood of sitting within the living sapwood—where flexibility is greatest—and outside decayed or brittle heartwood. This has the added benefit of providing room to create the back cut.

Why the Angle Matters

The angle between the top and bottom kerfs determines how long the hinge can function before breaking. In most felling situations, an angle of 70–90 degrees, between the top and bottom kurf, or greater provides the operator with maximum control through the arc of the trees fall.

Most straight trees on level terrain must arc 70–90 degrees before hitting the ground, though slope and tree structure can change this. The branches of trees with wide canopies tend to touch down sooner—often at about 70 degrees.

The open-face notch is a prime example of how to maximize hinge function with a open angle. With its wide aperture, it keeps the hinge intact throughout more of the tree’s arc of fall. This extended hinge function is what enhances safety and predictability.

To understand why angle matters, we need to look closely at the notch’s components and how they work together.

The Back Cut and the Hinge

After the notch is placed, the next step is making the back cut, which has two main purposes:

1. Deploy the piece (initiate movement)

2. Set the hinge thickness

   
   

Back cuts commonly fall into two categories:

• Conventional back cut

• Bore back cut

The back cut must be:

• Level

• Equal and even on all sides

• Positioned to create a well-proportioned hinge

  
  

The hinge is a uniform strip of uncut wood left between the apex and the back of the back cut. Its role is critical: it maintains control of the piece throughout the arc of its fall.

The thickness of the hinge is situationally dependent and generally ranges between 5-10 percent of the tree's diameter. It is important that the hinge is not too thick or thin and is left relatively level and even.

As the tree or section tips and the notch aperture closes, pressure builds on the hinge. Eventually, the hinge must break when the top and bottom kurf's meet together and the notch aperture is fully closed. The length of time it functions—and how predictably it breaks—depends on the angle created by the notch, wood quality, type and condition.

Situational Awareness: Choosing the Right Angle

No single notch angle fits every scenario or is exactly identical to the previous notch cut. This is because tree size, wood quality and many other site and tree characteristics are always changing. Operators must do their best and gain experience in safely, efficiently and effectively evaluating site conditions and tree characteristics such as:

Height

Lean

Slope

Structural shape

Species

When felling a whole tree with the goals of precision, safety and maximized control, the hinge should remain intact for the entire arc of movement, typically 70–90 degrees. This maximizes control and reduces risk by allowing the hinge to stay intact during the arc of the tree.

In negative rigging or treetop removal however, the hinge should break at a point where force is applied as evenly and in-line with the main stem of the tree as possible. The overall objective in these scenarios is to minimize dynamic movement down the main stem of the tree being removed. In these situations, estimate the angle which best minimizes dynamic movement when negative rigging or removing a top.

Arborists may also leave specifically selected limbs intact—known as mass dampening limbs—to help disperse energy and stabilize any dynamic movement down the stem.

Always Consider: What’s Your Angle?

When cutting a notch for felling tree, rigging, or removing a treetop, your safety and control start with one simple but essential question:

What’s your angle?

Understanding how notch angles influence hinge function—and ultimately the movement of the tree—empowers arborists to operate with precision, confidence, and safety.

Thank you for taking a moment of your valuable time to gain this deeper understanding of the notch—one of arboriculture’s most important techniques. Arboriculture Canada Training & Education is excited to continue supporting you soon, whether in the classroom, the field, or both! Until then...

Stay Safe & In Control!