It’s a standard symbol of self-destrucitve stupidity; someone is sitting out on a branch of a tree, sawing off the limb behind them, and of course when they cut through enough the limb breaks and they fall to the ground.
One TV show has as a symbol someone doing the same thing on a board sticking out from some construction.
But can it actually be done? My experience in sawing tree limbs or boards is that once you get even partially into the limb, or board, it flexes downwards and clamps the saw, making further sawing nearly impossible.
I’m not asking for volunteers, but has anyone ever heard of this actually being done (in the classic sense?) Any opinions on if it even could be done?
(Restriction - I’m talking about a vertical sawing motion ; a horizontal sawing motion might work, but that’s not how it’s ever shown.)
If your weight, and the weight of the limb, is not compressing the cutout, it won’t bind the saw. For a limb that could support a person, you should be able to get far enough through the branch without any binding for the branch to snap under your weight if you are sawing vertically, or horizontally across the top.
If you support a board or tree limb on both ends and saw in the middle, it will tend to flex to close the saw cut. But if the limb is supported at one end (the tree) and your sitting on the other side of the cut, it will tend to flex to open the cut.
It’s possible in as far as you will cut until the structure you are on fails and it breaks. If you are sawing the top, compression will happen below the cut. Actually your weight would facilitate non-binding.
It can be done with a chainsaw, because every now and again, people do it, often dying in the process.
I’ll see if I can dig up a cite, but within the last few years, I’m pretty sure there was a news story about a man cutting off the branch on which he was sitting, technically surviving the fall to ground, but being killed after the chainsaw and the branch fell on top of him.
It probably isn’t possible to cut all the way through a branch, but it should be possible to cut sufficiently far through that the remaining uncut timber at the bottom breaks or tears under the weight of the branch plus idiot tree surgeon.
Some of this will depend on the type of tree - some species have timber prone to snapping, others have flexible wood with long fibres that will mean the cut branch breaks and flexes downwards, but remains attached by the uncut portion.
Additionally, in pruning tree branches, the convention is to cut a little on the underside first, to prevent tearing of the bark, then start a cut from the top - two things will happen as a result of this:
-The lower cut will close up a bit, tending to allow the second (top) cut to open, preventing binding
-Cutting will proceed to a point where the branch *suddenly *detaches cleanly.
The limb can twist and bind the saw, and you probably are not sawing level with the ground anyway. Sawing at an angle between 45 and 90 degrees seems more likely.
You better test it OP, and have your next of kin report the results.
If you are in management, then surely you have minions you can get to try it? Then you can report back in person, rather than having your next-of-kin post the results.
I’d say it’s a form of poetic license. Yes, a horizontal orientation of the saw would work nicely, but it would be quite awkward, if even possible, for someone to do that while actually sitting on the limb. It would be distracting to the viewer to see the sawyer in the contorted position necessary for physical accuracy in the cutting. So the poor schlub is depicted in a natural pose, with the saw being close to vertical. Wouldn’t work well in practice but it gets the point across.
I’ve never sawed off the limb I was sitting on, but I did once get quite a scare when the limb I was sawing sprung up after the weight of the detached part was released, causing it to pop up higher than the ladder it had been supporting until that point. I was left holding on to the limb with one hand and holding the still-running chain saw with the other hand until my neighbor stood the ladder back up underneath me.
To answer the OP’s question, it depends entirely on where the center of mass of the part of the limb being sawed is. If the sawer is sawing vertically with a hand saw, the part being remove can swing one way, opening up the kerf, or it can swing the other way, pincing the blade. It just depends on where the limb wants to go.
Unless the part on the side of the cut away from the tree is being supported some how (other branches perhaps) or curves back on itself above the branch, it can only swing down and open the kerf. The center of gravity of the whole branch doesn’t matter. Only the center of gravity of the part outside of the cut matters. The branch could of course twist and bind the saw.
I believe that is what I said. I will be more specific:
If the center of mass of the part of the branch that is being cut is offset from the longitudinal axis of the branch, it will create a moment about the longitudinal axis of the branch. That moment, coupled with the vertical force translated to the vertical planar surface where the cut is being may result in a twisting motion that is resisted by the part of the vertical plane that remains uncut. That coupling may result in a translation in the axial direction of the branch. The direction of that axial translation is dependent on the direction of the moment. If the axial translation is in the direction of the saw blade, the blade will be pinched. If the sign of the moment is reversed, the axial translation will be away from the blade and the kerf will open. If the branch is symmetric about its longitudinal axis, then there is no moment and only the vertical force need be considered. In that case, a vertical sawing motion will result in a kerf equal to the set of the saw’s teeth until the shear strength of the remaining cross-section of the branch is exceeded, then vertical translation will occur.
This whole discussion ignores any internal stresses in the wood. Branches pinch quite often when you’re sawing them. Although, most of the time I’ve had them pinch, it was because there was another force acting on the other end.