Safe Chainsaw Use -- Kickback (Preview)Feb 23, 2022
that was a serious
kickbackaccident the worst thing that could happen to you if you are working with a
chainsawsince people started using
chainsaws in the 1940s and 1950s thousands have been injured or killed in accidents like that sure chainsaws are a lot
safer today, but bribery is still just as dangerous, people still get hurt and people still die, what can we do about it? Let's start by looking at exactly what bribery is and how it works. There's really nothing very mysterious or terribly complicated. its a matter of force and momentum in a chainsaw the force of the motor acts as much on the saw in one direction as the chain in the other but the chain is lighter and you hold on to the body of the saw so the sauce stays put and the chain spins now let me show you something a little more secure when we start the motor the force acts on both the body and the chuck but the chuck is lighter and i am gripping the body so the chuck turns around and the body stay put, but look what happens if we suddenly stop the moving part, all that force has to go somewhere to get the other part to start turning and you'll find out it's going backwards, that's momentum transfer, equal force, opposite direction, that's exactly what happens in a chainsaw
kickback, normally the chain spins, but when something grabs a chain and stops it when it's running under power, the same momentum transfer occurs cu When the chain is forced to stop the saw has to move in the opposite direction now when that happens there are only two variables we need to worry about the amount of force and the direction of movement the amount of force on the Kickback can be very little if the chain does not come to a sudden or complete stop the saw can just give a bit or bounce in the cut it happens all the time while cutting if the chain gets too tight or slows down even though the kickback is more severe and The saw can bounce out of the cut, which happens once or twice a day, but it's still pretty easy to handle if you hold the saw correctly, but it's when you're cutting at full power and something like that.
It happens that the chain stops suddenly and all the energy in a system goes into kickback and that's when the consequences can be really bad. That's where the second variable Direction comes in if you stop the string at the top of the bar. where it runs forward the saw goes in the opposite direction straight back if you stop the chain at the bottom of the bar where it runs towards you the saw jerks forward and here at the tip of the bar the chain runs in an angle forward and down at the same time if you stop here the saw will go up and back so that's really all there is to it when the chain is forced to stop and all that energy has to go somewhere and where it goes is correct. back to the saw and back to whoever is standing in the wrong place when you get there, now the next question is what can stop the saw so suddenly that it causes kickback. there is a pinch in the bar usually the most serious is the first what happens is that the cutters those cutting links in the chain are going around the nose of the bar that means they are pointing away from the bar at an angle if you let for that part of the bar to touch a solid wood branch behind the one you're trying to cut, for example, then that cutter can bite into it at an angle and go too deep, sometimes in fact it goes in so deep that it gets stuck when it's stuck, it stops the chain in an instant and when that shifting comes to a slam, we know what happens. its worst when the cha digs on the tip, the force is usually high and that's bad and the direction of course is up and back and that's very bad if that's where he's standing.
The second way the chain can be forced to stop is if it gets pinched by the wood you are cutting if you try to cut through a log from below in one motion for example you will see what happens when the log starts to break the two ends swing down the cut opens more at the bottom and closes at the top above is that closing at the top is a problem as it closes all the weight of the two halves of the trunk are pushing together and can pinching the chain so hard it stalls and then to the right the saw kicks back out of the cut the same sorts of things happen all the time really when you're cutting branches spring poles tend to be under tension being forced to bend when you've partially cut they start to break and start to pinch like so so kickback happens what we want to know is what can we do about it?
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