Chainsaw Cutting Techniques & Physics

Ever wonder why some branches drop cleanly while others pinch your chainsaw? Or why a tree reacts the way it does when you're making a cut? Today we're diving into the physics behind chainsaw cutting—how gravity, compression, and tension all play a role in how we break down this red maple.

So whether you're an arborist, landscaper, landowner, or just someone who wants to work smart with their saw, stick around and we're going to put chainsaw physics to the test. This red maple was cut down as part of a forestry project, and today we're going to be processing it into logs that are suitable to turn into firewood.

Before we get started using our chainsaw, we want to make sure we're equipped with everything we need to work safely out in the woods. Hard hats are going to protect our head from overhead hazards. Eyes make sure we're protected from flying debris. Ears keep our ears safe from loud noises our chainsaw is going to make. Chaps protect us from cuts that might not go where we want, keeping our legs safe. And suitable footwear with steel toes are going to help protect us from falling branches, falling debris, the equipment that's around us, and also give us better footing.

The first force we're going to talk about today is gravity. Because this limb is up in the air with nothing holding on to it below, we can pretty safely assume that the weight on this end is going to be exerted on our cut, making that branch fall right to the ground. This is the easiest cut we're going to encounter out here in the woods.

Knowing that all our weight is out here on the branch end, we can anticipate that this branch is going to fall. When we make our cut, the top of the cut is going to open up, and there's going to be compression on the bottom of the cut. So to safely make a cut like this, we're going to start with just a small cut on the underside of the branch. That's going to allow any of that compression to have a little room to work and not rip our bark. Then we're going to finish our cut on the top.

In this situation, we have a different type of force at play. On both ends, we have upward pressure being exerted up from the ground and from the rest of the trunk of the tree. We're cutting at a low point. The right side and the left side of this are both being held up or pushed up by the top of the tree, the ground, or from the rest of the trunk.

What this is going to do is cause compression on the top of the log that pushes the two parts of our cut together. On the bottom, they're going to be getting pulled apart. This is a very common situation to see someone get their saw pinched. So how we're going to prevent that is we're going to start our cut on the top of this, opening it up just a little bit to relieve some of that pressure and have a spot so that we have a nice controlled drop and the bark doesn't tear. We're going to make the majority of our cut from the underside. This is going to allow us to safely make this cut without pinching our saw, and we should see the bottom of the cut just slowly start to open up nice and controllably.

All right, so we talked about gravity, especially out on longer limbs where the downward pressure is away from us and on the end of the limb where that limb is going to fall down when we cut it. And we talked about compression and forces acting in an upward nature on both sides of the log we're cutting that cause the top of the log to pinch. So we make that underside cut so that the underside opens up.

Even the most experienced sawyer sometimes misreads a log. So what do we do if we start to recognize that our saw is getting stuck and we want to safely proceed with the cut? Here we can see those compression forces working on the top of our cut. The top of the log actually comes together and binds this bar of the saw. It actually pauses the chain from moving and makes it really hard, and that saw starts to bog down.

So what we're going to do is drive a wedge into the top of that cut to open that cut back up so that we can get our saw out and continue our cut on the bottom. We can see the log opened up much more at the bottom here and it's much narrower up top. So we have that compression force up on the top of the log where both sides are putting pressure on the cut downward causing this to close up and the bottom to open.

We recognize that at the top of the cut, and as soon as we started to feel the saw pinch, we're able to put the wedge in. That way we didn't have to fight the log to pull our saw out. We were able to nice and easy drive the wedge in, make just enough of an opening to get those separated enough so that we could easily pull up and out safely on our chainsaw and then finish the cut from the bottom.

So there's a quick overview of chainsaw physics. Stay safe out there and happy cutting.