Not sayin’ a bar won’t cause the problem you describe, but I can get pretty lax on dressing my bar rails when I’m doing a lot of cutting, they’ve gotten way out’a whack at times and I don’t have curving-cut problems. I’ve even bent a bar, straightened it the best I could in a tree crotch and finished out the day without have a curving-cut issue.
The only times I’ve had my saw cut in a curve (especially to the point where it binds) is because I screwed-up the sharpening job. One thing guys tend to do is file the cutters on one side of the chain just a tiny bit shorter then the other side… it has to do with the way pressure is applied when the chain/bar/saw is flipped around and the angle direction changes. Over a few filings all the cutters on one side get enough shorter to cause one side to “bite” into the wood more than the other side (even if the depth gauges are set for each cutter). Yeah, I’ve been-there-done-that, and I’m still fully capable of screwing-it-up when I’m filing in the field and get in a hurry. Sometimes the difference in cutter lengths is easy to see, but often the left/right cutter angles will play tricks with (older?) eyes and hide it from you. What I do, every half-dozen or so sharpenings at the bench, is grab a micrometer and measure several random cutters on one side of the chain to get an average length, then do the same on the other side… those two averages should be darn close, say around .005 of an inch, give-or-take. And really, if you measure all the cutters on the chain the difference between the longest and shortest should be no more than .020, maybe .025 of an inch (ignoring the occasional random mangled cutter), .015 would be better… if you have a wide variance of cutter lengths some of them will just “float” over the wood without cutting much, and the chain will cut “rough”. Don’t forget to set the depth gauges after “fixing” the cutter lengths. After you’ve had to “fix” a few chains you’ll figure out what’s happening, then modify your sharpening technique, and will only rarely need to “fix” one.
Another filing error that will cause the saw to cut in a curve is getting the angles different on the two sides of the chain, again because of the perspective you get when it’s flipped and filing angle goes from left to right, or right to left. If you’re filing all the cutters one side at, say 28[sup]o[/sup] and the other side at 32[sup]o[/sup] it’ll “bite” more on one side than the other. Same thing if you’re pushing the file deeper in the gullet or tipping the file differently on one side of the chain.
It ain’t so much that every cutter has to be an absolute perfect mate to the next… and they won’t be. But it is all about consistency when going from one side of the chain to the other.
