Chainsaw Binding

Consider the physics, and prevent chainsaw binding while in the woods.


| September/October 2017



chainsaw

The log is a beam, subjected to the forces of compression, tension, torsion, and shear.

Photo by Getty Images/inagorny

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 (Figure 2). 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 (Photo 1).

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 (Photo 2). 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 (Photo 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).





mother earth news fair

MOTHER EARTH NEWS FAIR

Feb. 17-18, 2018
Belton, Texas

More than 150 workshops, great deals from more than 200 exhibitors, off-stage demos, inspirational keynotes, and great food!

LEARN MORE