Tree Falling Puzzle

[bergerud]

When felling a tree, one first makes a wedge cut about 1/4 of the way into the tree. Then one makes a horizontal back cut above the wedge more than halfway through the tree to leave a small hinge of wood. The tree now falls over in the direction of the small wedge cut. (See the picture I found on the web.)

The puzzle is this: How is it that the tree falls toward the wedge cut when the center of mass of the tree is clearly over the other side of the hinge? It seems that loggers just follow the procedure to cut down trees and are not bothered by this apparent contradiction. I have never heard an explanation of why the tree falls the way it does. Any theories??

[fwharris]

I will take a stab at it.

As the feeling cut is being made it releases the tension on that side of the tree. Since the scarf cut has already weakened that side of the tree and the weight of the tree is already forced that way... TIMBER!!

[unitedcases]

So whichever you want it to fall thats the direction you cut your scarf cut?

[bergerud]

So whichever you want it to fall thats the direction you cut your scarf cut?

Yes, the scarf cut is the direction of fall even thought it is only 1/4 way into the tree.

I will take a stab at it.

As the feeling cut is being made it releases the tension on that side of the tree. Since the scarf cut has already weakened that side of the tree and the weight of the tree is already forced that way... TIMBER!!

That would make sense if the tree leaned after the scarf cut but it does not. The tree only moves after the back cut is made. The cm is still on the wrong side of the hinge.

[MikeON]

I'm hardly an expert but have dropped a few hundred trees. You seldom get a perfectly vertical tree with the weight of the limbs equal the whole way around. Yes, sometimes the tree will try to go back and pinch the chainsaw bar. For this reason, I use wedges on all trees except those with obvious lean in the desired direction of fall. You can even make a tree with a slight lean in the wrong direction go over center and fall in the desired direction, using wedges. When making the back cut, drive in wedges behind the bar as soon as the cut is deep enough.
The notch shown in the opening post is about 45°. The problem is that the tree must fall about 90° to hit the ground. So the notch will close up and the hinge must break to continue the fall. This can cause the trunk to split, ruining good timber. Search for "open face felling notch" and you will see lots of articles about making the notch close to 90°. Here is one example:
http://www.treeservicesmagazine.com/article-1461.aspx

[brdad]

The way I remember it explained to me has to do with vertical compression of the tree. After both cuts are made, the felling cut side of the tree only has the width of the saw blade to compress, while the scarf cut side of the tree has from the top of the felling cut to the bottom of the scarf cut. There was more to it than that which I can't fully recall.

[Smoken D]

#4, main felling cut, I have always come in a downward direction 25 to 30 degrees. Where I live never a tree on a flat surface always hills. But, don't go by me, though has always worked for me. And yes hundreds of trees I have dropped, not one come back.

[bergerud]

The way I remember it explained to me has to do with vertical compression of the tree. After both cuts are made, the felling cut side of the tree only has the width of the saw blade to compress, while the scarf cut side of the tree has from the top of the felling cut to the bottom of the scarf cut. There was more to it than that which I can't fully recall.

That is my theory. The hinge compresses under the weight of the tree. The length of the hinge on the front side is longer and compresses more. This causes a torque which is more than the torque of the cm being on the wrong side. A stump or a small tree will fall backwards because it does not have the weight to compress the hinge. The compression of the hinge causes enough torque to fall trees which are even leaning the wrong way. I have done that many times.

Brdad, I have never come across an explanation of this. Who did you get the explanation from?

[skeeterman]

when i cut trees down you can be guaranteed they usually fall toward something valuable ,such as house , pool or auto lol.

[brdad]

That is my theory. The hinge compresses under the weight of the tree. The length of the hinge on the front side is longer and compresses more. This causes a torque which is more than the torque of the cm being on the wrong side. A stump or a small tree will fall backwards because it does not have the weight to compress the hinge. The compression of the hinge causes enough torque to fall trees which are even leaning the wrong way. I have done that many times.

Brdad, I have never come across an explanation of this. Who did you get the explanation from?

My father worked on logging equipment for a living and I attended logging shows and seminars with him on occasion. At one of these shows at least 20 years ago there was a demonstration explaining the process and why the scarfs are cut a certain size and why the height of the felling cut in relation to the scarf cut was important. It was intriguing because the science of the cut was discussed as opposed to basic techniques and safety which was typical in such discussions.

I looked some online as I am sure you have and can't find anything to back that theory up however. I'm surprised at that...