Learn how to cut a tree on the ground with a chainsaw while considering the physics of preventing chainsaw binding in the woods.
Just about anyone who has used a chainsaw has been there: One moment you’re happily cutting a log, spitting out a nice plume of wood chips, when suddenly, everything comes to a sudden stop. The log moved one way or another and wedged the saw tighter than the lid on a pickle jar.
Your first response is to see if you can wiggle it out. But that almost never works, and you just wind up stretching the chain. Next comes a string of expletives that would make a drunken sailor blush. Offhand, the only thing I can think of that is more annoying (and humiliating, if someone else happens to be present) is when you wedge a second saw trying to cut out the first one. I suppose, with enough saws, you could eventually cut your way free, but with a little forethought and a couple of plastic wedges, that first one won’t get stuck in the first place. Here are a few tricks I use out in the woods to keep from getting all in a bind.
First, let’s take a look at the problem from an engineering perspective. The log is a beam, subjected to the forces of compression, tension, torsion, and shear. Shear is good — that’s what you want the chainsaw to do. Tension is trying to pull the log apart, compression is trying to push it together, and torsion is trying to twist it. We’ll deal with torsion later. Unless the log is flat on the ground, it will have both tension and compression. A beam supported on both ends has compression on the top of the log and tension on the bottom (Figure 1A). A cantilever (supported on one end and the other end hanging) has tension on the top and the compression on the bottom (Figure 1B). Either way, it is the compression that pinches your saw. To make matters more complicated, it is often hard to tell which kind of beam you are cutting. Even an experienced logger won’t get it right every time. But if you pay attention, you’ll get through it without any problem.
Let’s start with a log supported on both ends. If you start cutting from the top, at some point the cut will close up and pinch your saw. The best way to deal with this situation is to cut down about two-thirds of the way through the log — or until the saw kerf just starts to close up above the bar. At that point, stop, engage the chain brake, pull out the saw, and drive a plastic wedge into the top of the kerf to hold it open. You can use the heel of your hand, or tap it in with another wedge just enough for it to stay put. With the wedge in place, you can proceed with confidence.
Often, you can use the wedge even if you cut too far and the saw gets stuck — great for helping someone else to free their saw without putting yours at risk. This takes more force. I usually drive the wedge in with the flat end of a single bit axe. Sometimes, it takes a second wedge driven in at a different angle, so always bring a couple out to the woodlot with you.
A log supported on one end (cantilever) should, in theory, be no problem, since the kerf opens away from the chainsaw bar as you cut downward. Practice is a whole ‘nother matter! Everything goes fine until the end of the log drops down and binds against the bar due to compression (Figure 3). This often happens on the first cuts after a tree has been felled, and the branches are pushing against it. Usually the saw is easy to dislodge, since you have your wedges and single bit axe handy. If the free end of the log is high enough off the ground, it can split before you cut all the way through, wedging the saw in place like a vise (Figure 4A). To avoid this, cut upward from the bottom about a third of the way through the log, then finish the cut from the top (Figure 3). Be careful: The log will hit the ground fast! For more control, you can make a “V” notch on the bottom, and the log will come down more slowly (Figure 5).
Torsion (twisting) is the toughest to work with, because you usually cannot see it, and it works in some very unpredictable ways. Usually this stress is caused by branches creating an uneven force on the log. It is also very common when cleaning up after a tornado. The biggest hazard here is that the log can roll. Any time you are cutting a log still attached to the top, this is a possibility. Keep a close watch for any twisting as you cut. The best way to deal with this stress is to have a wedge handy and drive it into the saw kerf before the wood starts to move on you. As always, if you feel you’re out of your league, don’t try it.
Sometimes, you can also use wedges if you misjudge the lean of a tree. Drive a wedge into the back cut kerf to try and lift the tree off your saw. Then drive it on in to persuade the tree to fall in the intended direction. You may need to stack two wedges to fell the tree, but you’d be surprised at what they can do. Plus, it is much safer than tying a rope or chain to the tree and pulling it with your old pickup truck.
The techniques in this article will prove much more useful if you practice them so you can use them with precision when necessary. And if all else fails, you may want to remove the chainsaw from a hopelessly pinched bar before you head in for the day.
One last note: logging — or even firewood cutting — is dangerous work. Wear full safety gear — boots, chaps, logger’s helmet, and eye and ear protection — and spend time with an experienced woodsman for appropriate training.
Wedges
Most places that sell chainsaws also carry plastic wedges. Make no mistake, they can take a real beating, plus they are designed not to pop out of the saw kerf when you hit them. Don’t use steel wedges. When (not if) you hit the wedge with the chainsaw, it is much better to cut into plastic than hit steel and have metal shards flying out at you and destroying the chain. I usually carry three 6-inch wedges with me. When in a bind, I’ll even cut wood wedges out in the woods, though that has to happen before getting the saw stuck. Sometimes I have to sacrifice a wedge and cut it with the chainsaw. That’s just part of the job. But save the heirloom steel wedges for the splitting station or another use with maul instead of saw.
Critical considerations for choosing the right chainsaw, with Hank Will.
Dave Boyt manages a family tree farm and operates a portable sawmill in southwest Missouri. He is a certified Master Logger and has cut all the firewood to heat his home for more than 30 years.
