Maximum computed kickback angle 45 deg.?

[Oregon Engineer]

My gracious! That is awful......I guess that is a worst case scenario... Is the bar nose hitting a foreign object or another piece of wood usually what causes severe kickback like this?

It was not the most severe encountered on the test rig, some combinations are worse. If you are using professional chains, yellow label, keep your chain brake in good working order. The brake is supposed to stop the drive sprocket before the saw rotates 45 degrees. You may still get hit, but the chain should not be moving. If you are hunched over your saw while cutting and there is less than a 45 degree angle between you and the bar, you may be kissing a moving chain.

The bar nose is hitting a medium density fiberboard block. The MDF board is used in place of wood to keep a consistent test medium. The MDF board is selected based upon density.

 

[pbtree]

Oregon Engineer,

Most excellent video - it brings home how fast a helpful tool like a chainsaw can turn into your worst nightmare.

 

[Ekka]

Kickback kick back video

The attached .mov file shows a kickback on the test rig. The movie started at 9 megs and I got it down to 1/2 a meg. It's short but you will get the point if you picture yourself behind the saw.

I have managed to load up to the AS server a WMV version of this. It also features a SLOWED DOWN view at 10% of the normal playing speed.

 

[Islander]

Any other videos on kickback?

Wow that video is something. I was trying to estimate the time it takes for the saw to lunge backwards...it looks far less that 1 second. Seems like the saw is in completely out of control...a person couldn't possibly respond anywhere near that fast.

I recently got a bigger saw, and could use some education on this subject. I've been completely impressed (safety wise, not cutting performance) with the anti-kickback chains and bars on other saws I've used...I can't get them to kickback no matter what I do to the tip of the saw. One safety chain I have just doesn't cut anything on the tip of the bar. If you bury the bar it just stops cutting on the end, which is annoying but clearly safer. I know there is a big price in cutting speed.

Are there any other free resources to learn about this aspect of chainsaw safety? I'd rather not see a moving chain that close to my face!!

 

[ford832]

Excellent video Oregon Engineer but watching it gave me the heebie jeebies.Cripes,imagine that kissing your forehead.

 

[Erick]

Excellent video Oregon Engineer

So which saws are the worst for kickback the small light saws or the big cube long bar set-ups?????

Seems like it would be the smaller high reving saws would be the worst, but the power of the big boys might be tougher to tame???

What do the tests say?

 

[Oregon Engineer]

.......Are there any other free resources to learn about this aspect of chainsaw safety? I'd rather not see a moving chain that close to my face!!

Here are a few other sources of information. An internet search under Kickback or chain saw safety will bring you another several thousand sources.



http://www.oregonchain.com/precautions.htm

http://www.worksafebc.com/publications/health_and_safety/by_topic/assets/pdf/chainsaw_safety.pdf

http://www.ag.ndsu.edu/pubs/ageng/safety/ae1025w.htm

http://www.osha.gov/SLTC/etools/logging/manual/logger/chain_saw/chain_saw.html

 

[ryno]

Oregon Engineer, does that test rig provide any resistance to the rotation of the saw? Or does it allow it to pivot on its center of gravity with little resistance?

I think if the operator had a weak grip on the saw and it was pulled from his/her hands that is what it would look like.

Very scary!

 

[Oregon Engineer]

......So which saws are the worst for kickback the small light saws or the big cube long bar set-ups?????

Seems like it would be the smaller high reving saws would be the worst, but the power of the big boys might be tougher to tame???

What do the tests say?

1) Biggest factor is professional chains without any safety features.
2) Then comes light weight higher power saws, but don't be fooled the heavier saws have the power to over come their weight.
3) Short bars will allow for an increase in the rotation.



Ever test your chain brake? Once you activate it the chain should stop what appears to be instantly. It should stop the chain before it can contact you.

A little advice from some guys who investigate accidents.
http://www2.worksafebc.com/i/posters/1999/ha9907.html

 

[Oregon Engineer]

Oregon Engineer, does that test rig provide any resistance to the rotation of the saw? Or does it allow it to pivot on its center of gravity with little resistance?

The saw is mounted so its center of gravity is aligned with the axis of rotation of the rig. As the saw rotates back it lifts a weight so the total rotational energy can be measured. If the saw did not lift a weight to slow it down it would rotate so fast it would look like a fan blade.

The carriage holding the coupon is weighted to have the same weight as the saw. As the carriage moves back after the kickback it lifts a weight so the linear energy can be measured.

 

[ryno]

Is the resistance of the weight even close to the resistance that would be input from an alert operator. If its not the test is really only showing us the potential of kickback if the saw was let go or loosly held in a kickback situation. I'm not saying the test isn't a vauleable lesson. It just isn't putting the operator input in the equation.

In that same rig if the saw is allowed to pivot on its center of gravity, how violently does it move if it is reved from idle to WOT without being held. On a good runnig saw with a average size bar (20-24)" there is a lot of centripital force that is generated when accelerating. Once it is at a constant RPM it would balance out.

 

[Oregon Engineer]

Is the resistance of the weight even close to the resistance that would be input from an alert operator. If its not the test is really only showing us the potential of kickback if the saw was let go or loosly held in a kickback situation. I'm not saying the test isn't a vauleable lesson. It just isn't putting the operator input in the equation.

The mechanical test is done to measure the energy exerted by the chain/bar/chainsaw from a kickback event. The test rig itself does not simulate a kickback as if an operator was involved. The information from the test rig is input into a computer program that generates a "computed kickback angle" to give a measure of what would happen if it was in your hands..

From the kickback standard:
"The computed kickback angle is determined through a mathematical simulation of the motion of the chain saw during kickback. This simulation is contained in a computer
program. The computer program contains equations that represent the reaction forces exerted by the operator on the saw during kickback. These equations are based on analysis of high-speed films of simulated kickback tests."