Thanks for filling in for Gypo, Mike.
I have looked a lot of things up just for the sake of doing it, I'm not denying that. In this case I'd looked it up to see why I was seeing what I was seeing in practice. I've gone through a fair number of chains, sprockets, bars, and even saws.
I cringed when I saw that Brian had posted between the time I'd fetched the thread and originally replied myself. It's ironic that we'd unknowingly agreed that it was a result of the chain impacting the bar. The difference was in that I'd said it was because the chain was too loose (implying that it was continuing off on a tangent) and being too violently snatched back to the bar. If there's enough tension in the loop, it doesn't attain that free flight around the tip.
I suppose there could be a situation where the nose sprocket has enough of a mismatch in pitch or tooth/driver fit tht it might tend to "hang on to" the chain, resulting in a violent extraction, but in such a case there should obviously be something amiss when running the loop by hand. Also, I'd think the wear would be in the bar rail right at the interface with the sprocket (pretty much in line with the sprocket axle) as opposed to say a chain-pitch distance back toward the saw that the loose chain would produce.
Brian's claim that a too-tight chain will induce wear on the bar rails might also be valid regarding wear right at the tangential point where the bar meets the varying sprocket pitch diameter.
I guess it comes down to exactly where the damage is being done as to what the cause is.
After leaving the drive sprocket the chain will also hit the bar too hard if it's too loose, for different reasons than at the tip, but it's still not the direct result of some flexible thing which had been travelling captive in a circular motion and desiring to stay in that mode.
Glen
