Archive for August, 2010

Back-Cuts, Hinges & Control (Article 6)

Monday, August 2nd, 2010
 

This is the last in a series where I have been discussing a sequenced planning method to tree felling.  When read in sequence, the articles combine to describe an effective tree felling planning process. It has been my intention to encourage readers to think about many aspects when felling trees – with the focus being on tree faller safety.

It is important to remember that some tree felling techniques developed from years of trial and error and in field practice and in all cases deserve our respect and acknowledgement. It is difficult to produce conclusive scientific data that verifies certain aspects of tree felling techniques, due to the many variables that are at work when dealing with living organisms such as trees.

Remember that new tools cannot get into a toolbox when the lid is closed.  An open mind is like an open toolbox and new tools when tried and proven are a wise addition.

In most cases, the back-cut is the final step when felling a tree.  The back-cut removes the wood left preventing the notch from closing, it also forms the hinge wood. The hinge wood is the wood left uncut behind the notch and is what provides control and guidance to a felled tree. It is important to understand that the hinge can only offer control as long as it can work; when the hinge fails, control is lost.

Cutting & Forming the Hinge
 

Traditional Back Cuts

A crosscut saw was the tool of choice and for generations back-cuts were cut by hand with a crosscut saw, cutting from the back of the tree towards the notch.  The modern chainsaw and tooth design offers us alternatives to this traditional method. The notch selected should be considered when deciding where to place the back-cut. Traditionally it has been recommended to raise back-cuts above the apex of the notch.  This technique (called the stepped back-cut) forms a step or back stop and minimizes a tree from sliding backwards off the stump causing great risk to the faller. It is important to raise back-cuts whenever felling a tree with a small notch opening such as 45 degrees or less. In these cases, the hinge will have to break when the face notch closes. After all a notch with a 45 degree or less notch aperture will have to break the hinge and as a result will lose control when the tree in most cases is only half way to the ground. A limitation of a small notch aperture is that it forces hinge failure before the tree reaches the ground, thus causing loss of control and gravity takes over before the tree is on the ground. If limb tying or felling obstacles are present that could snag the falling tree a stepped back-cut is also advisable regardless of notch opening.

Open Face Notch

Tree Felling Notches (Article 5)

Monday, August 2nd, 2010

Many times when workers discuss tree felling notches, the conversation ends up being about what kind of notches are used and what they are called.  Typically your hear about a common notch, a Humboldt notch, an open notch, and less frequently a v-notch, or swing notch. It is important to give techniques names because it helps identify one from another; however, it can also cause some problems. Typically when you learn a notching technique you identify the notch with a name and the learner connects the sequence of cuts and angles to that specific notch. This is typical basic training, however, I believe it is equally important to include an educational component that explains the ‘why’ behind the ‘how’. This leaves a worker with an understanding and the ability to make wise choices in order to achieve specific results.

Education is understanding how something works; training is knowing how to perform a technique that works. I find in many cases individuals who have been falling trees for a long time were never educated about the origins or reason why the technique was developed and simply repeat the same traditions, not giving thought to what the notch is, what the notch does and how it can be cut to enhance and achieve desired results. The fact is we learn so much about falling trees and cutting notches by doing and we tend to follow what we saw from those that cut before us.

A powerful example of this is the common notch.  The common notch is typically cut with a 45 degree opening.  Why a 45 degree opening?  The explanation of why lies in history. The modern day chainsaw has only been in use realistically since the 1950’s, which means for many years prior the tools available for cutting notches were different. The tools most commonly used in North America since the arrival of the white man was the crosscut saw and axe. In order to cut a notch in a tree with a crosscut saw and an axe, the first cut is sawn perpendicular to the grain of the tree with the crosscut saw. Next, an axe chips the wood out using downward angled strikes; it is interesting to observe that an axe chips out wood best at a 45-degree angle to the wood grain. It is reasonable to deduce that the 45-degree common notch is a result of the limitations of the tools available at the time. Many cut the same notch today as it was done hundreds of year ago. Some consider that this notch was technically developed yet history suggests otherwise, the 45-degree notch is largely the result of tradition and older equipment limitations.

What is a notch and what does it do? A notch is an opening made into a tree trunk by making two angled cuts into the trunk with the intention being that the notch starts the tree falling in the desired direction of the fall and dictates how long the hinge can work and when it will have to break. From a mechanical point of view this notch in the tree changes the gravitational load forces on the remaining wood fibre, and the wood fibre left behind the notch is referred to as hinge wood.  I will discuss hinge wood and tree falling control further in my next article.

Therefore rather than focusing on what a notch is named or called, let us look at what we want the notch to do for us when falling trees. Whenever I ask students if they would like to learn techniques that would improve safety and control of falling trees they all raise their hands or nod their heads in agreement. I must say that I am speaking in this article about notches that specifically focus on maximizing safety and control. The notching technique I am speaking of in this article is not a typical production falling notching technique. The technique has many technical considerations that are necessary to allow other important aspects of the tree falling process to work better and longer, such as the hinge. This notching technique is not based on tradition and equipment limitations as it requires fallers to think and plan and not simply follow a cookie cutter routine.                                             

In order to improve safety and control when falling trees it is important to aim notches in the desired direction of fall and ensure that the completed notch opening or aperture should be of sufficient degrees to allow the hinge to provide control all the way to the ground. It is also important that the two cuts made to form the notch meet evenly and have no by-pass as this can encourage premature hinge failure. 

The following simple three-step notching plan can help anyone achieve consistent and repeatable notching results.

Step 1

Determine the angle formed by the trunk and the ground level; this angle should be the same as the angle or aperture of your notch opening. This will ensure that your hinge has every opportunity to work all the way to the ground giving a greater degree of control. Trees grow nearly perpendicular to level ground so often an opening of 70 to 90 degrees is common. However, trees growing on heavy slopes will always try to grow parallel to the force of gravity, this plant response is called geotropism, and in some cases the angle created by the trunk and the ground level is well over 100 degrees or well under 45 degrees.

Open Face Notch

Step 2

Stand beside the tree and behind your saw, with your chainsaw positioned to begin cutting the top cut of the notch aiming the sights in the direction you want to fall the tree. The felling sights are raised ridges, indentations or black lines and are located on the top and both sides of the saw body on most professional model chainsaws. Wherever these sights are pointing when cutting the notch should indicate the direction the tree should start to fall. (NOTE: many factors dictate where a tree will fall and an aimed notch does not guarantee the tree will fall in that direction.)

Line up your felling sights

Step 3

Make the top cut first, and then the bottom cut of the notch. By doing this you can use the kerf created as a window to know when to stop cutting when making the final cut in order to avoid by-pass or mismatching. It is important to have even alignment where the top and bottom cut meet.

Make your top cut first

Following these three simple steps can improve your safety and control when felling trees.  As often is the case with working with trees, chainsaws and gravity, there is no substitute for hands on practice, coaching, training and education. I always encourage people to attend hands on courses and attend seminars – after all education is a journey. It is my intention to stimulate thought with this article and get fallers to think about why they make the particular notches they make, where the techniques originated and why it developed. I have never seen one tree the same as another so why should we use a notching technique that is the same for every tree. In most cases it makes sense that techniques evolve that are similar and have common trends and that is a good thing.  Just remember that repetitive complacency is a silent killer. Avoid mindless routine, challenge yourself daily to think through your work and make adjustments regularly even though they may seem minor. This engages your mind and stimulates learning.

In closing I want to tell you the name of this notching technique; it is called ‘the open face notch’, I think the name in this case says a lot, ‘open face, open mind’.

In my next article I will explain how the back-cut and hinge work together with the notch.