Reasons for throwing a chain?

I have never seen a chain come off a sprocket or bar but I seen many cases for saws on eBay.. that show scrapes and gouges on the case that must be evidence of a thrown chain. How does this happen?...worn sprocket?.... loose chain? I would like to know because surely this can be very dangerous to the operator… thank you..

Lazyness to keep it tight is prob #1...Bob

Sierraazul said:

I have never seen a chain come off a sprocket or bar but I seen many cases for saws on eBay.. that show scrapes and gouges on the case that must be evidence of a thrown chain. How does this happen?...worn sprocket?.... loose chain? I would like to know because surely this can be very dangerous to the operator… thank you..

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i think that having a loose chain is part of it, but if you are not making a straight cut, in other words your trying to twist the bar while cutting (im not talking about a diagnol cut), then you can throw chain, or if you get pinched and your tryin to yank it out while pulling trigger. maybe other people know better than I . . . but this has been my experience.

Most of the time,when you cut branches,small stuff 1-2 in .even if the chain has the right tension.Ive got chain hit my legs many times only cutting my safety pants.

Cutting small branches or saplings with a chain that isn`t tight will also cause a chain throw.

Also too large of a sprocket that does not match the heel size of the bar causing the chain to travel through mid air before re-entering the bar groove.

My wife calls me "safety pants"

The two main causes of chain throws too long a chain, ie., to much space between sprocket and heel of bar. Also worn tolerance between drive links and bar groove.
John

My wife calls Gypo, "hot pants", and "very, big, tipper"

Bob Wright said:

Lazyness to keep it tight is prob #1...Bob

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Not necessarily. Obviously if your chain is too loose your odds of throwing it are better, but when you are hustling and limbing up a tree many things cause a chain to be thrown regardless of how tight it is or insn't. In brush, many times I will throw a chain sawing it out of my way, limbing up a tree and your tip hits the base of a limb while still moving at high RPMs often you will throw your chain. Of course a good sprocket and tip help. But in my line of work when hustle pays the bills chains get thrown very often, and my equipment is kept up, and I run a properly teniosioned chain.

throw

So THAT is what happened at the get together. And I was blaming the cookie hitting it all this time.

What do you consider too loose chain? If your bar tip and sprocket are OK you HAVE to be somewhat loose to throw it. Only times I have had thrown chains have been on horizontal or diagonal cuts with looser than normal chain. Never thrown one while making vertical bucking cuts...even with a sagging chain...just make sure the saw is up to speed before starting the cut. With small stuff you are starting and stopping more often and that would give you more situations and angles to toss a chain.

Bars and chains wear out. We could throw out abuse, improper maintenance as part of those wear out events.
Ever seen where the bar has been chipped away just prior to the sprocket? Probably run too loose and it was slapping the bar in that area.
That is a spot where a limb could assist the chain on a 2 minute break from work.
Not only does running a loose chain increase a thrown chain risk, but it also can contribute to uneven bar wear that can make it where you can't stop the chain from choosing its own path away from the bar grooves.
One should tighten new chains at least every gas tank and check tension every tank after break-in. Flip your bar periodically. Have a local saw shop take the rails down and bring them back together as needed.
Have a tendency that every time you replace a bar put a new chain on that bar, not an old chain that has acquired bad work habits.
Don't cut above your head unless you want a thrown chain in the face/neck. Unless you want to go out on a medical where the jury doesn't want to contest your claim 'cause they can not look you in the face.
Don't run a saw that isn't oiling, not for a second.
Actually clean the bar grooves just for grins.
How muck to tighten a chain depends on the bar you're running.
Hard nosed (oldest style) have to be run loose.
Roller nosed (a couple decades back but coming to life on ebay) moderate tension.
Sprocket nosed (current technology-the best) can be run fairly tight.
Tight is where you pull the chain (saw not running) up away from the bar and it only rises up until the guide drivers just clear the bar.
Loggers with 36"+ bars like to run their chains really loose and just spring the bar and pop the chain back on. No bar nut/chain tension screw use needed. This is partly because a loose chain is less resistance and it functions about as well as a moded muffler for effective power increase. Don't try this at home, generally.

I agree with most said before. The weared bar, which lost its ellipsoidal shape (some times even has concave) is making correct chain tensioning rather impossible. By the feeling such old weared bar has a decreased cutting speed too. Longer bars (chains loops) should be more prone to the chain throw than shorter

possibly could be the wrong bar oil or even worse the wrong octane gas.

When a customer brings in a saw with a thrown chain, or really loose chain, and the
bar nuts are super tight, almost always I find a wore out sprocket. Convincing them
they need a new sprocket AND a new chain can be difficult, because they think I am just trying to increase sales

The times I've thrown chains came with a loose chain and/or cutting sideways on limbs or cutting hazelbrush. Got "nipped" one time (black & blue) mark on my leg, but that was all.

Both times my saw lost a chain from the bar grooves, (the safety chain-catcher caught it and prevented the chain from slapping around) it was caused by the inertial chain brake engaging. The chain didn't break open (stayed in a loop). Taught me to move slowly and avoid lifting/levering the saw while the chain is moving. Glad that this saw's designers thought ahead about dumbheads like me.
Stihl MS290.

I've sawed a lot of firewood in my day and only had teh chain come loose when itw as not properly tensioned, the chain broke or something of thatnature. The closest I ever came to getting hurt with my saw was when I was making split rails with my 025 and soime ripping chain...I thought the tensionw as enough but I guessit had gotten loose, the chain came loose and hit me in the knee. I just gota little nick from it, but if that had been regular 35LG or 26RS chain like I normally use, I would have had a good cut on my kneecap. Other times was before I knew what I was really doing and had crappy saws and didn't maintain them as well as I should've because of ignorance. One time the liitle homelite let go of it's 63PM1 chain casue the chain broke in some exceptionally hard live oak, no injury to me or the saw, just needed a new chain,