Saw Won't Cut Straight -
Bad Bar or Bad Chain?
Chainsaws should cut smooth and make straight cuts, but sometimes they don't. When a saw's cut pulls to one side or the other, it makes it hard to buck, hard to line up undercuts, -- and in general, hard to get a cutting job done. Every professional saw user has experienced this to some degree, and it is frustrating.
Most of the time when a saw won't cut straight, it's caused by a problem with the saw chain.
When a saw won't cut straight, the first component most users look at is the bar. It seem logical a bent bar would cause this, because it is is what guides the chain. If they find a little bend in the bar, they figure they've found the problem. Some will straighten the bar, others will replace it. Unfortunately for most, the saw's cuts still pull in the same direction after the repair.
Most of the time, when a saw won't cut straight, the chain is the culprit. The example above shows top plates that are unequal. This causes each tooth to take a different sized bite of wood. Since a saw chain is a "team" of cutter teeth, the cut will pull in the direction of the side whose cutter teeth take the biggest bites. It is as simple as that.
Sharp On One Side - Dull On The Other
All cutter teeth should be sharp, filed at the correct angle, and be the same length. Usually this is easier to accomplish with a grinder than it is with a file. When hand filing, this must be done by eye. On a grinder, the angle, depth, and length can all be preset. This makes it easier to duplicate each cutter tooth. When filing, it is more difficult. Those of us who are right-handed often do a good job sharpening the left side cutters, yet find in more difficult to sharpen those on the right side. Those who are left-handed have the opposite experience. After several filings, a chain will usually show the effects of this. Teeth on the side easiest to file are usually sharper but shorter. The other side has longer teeth, but may remain dull even after filing.
People who use grinders are not immune to inaccuracy. Adjustments must be checked occasionally to be sure ALL the damage is being removed from ALL the cutter teeth. It is also necessary to check to be sure all top-plates are equal length. Grinders do not make you infallible.
Pulling Problems That Are Hard To Diagnose
Some cut pulling problems are hard for even experienced saw users to diagnose. We occasionally see a fellow with cut "pulling" problems that has a bad bar plate or a dawg bolt that sticks out a little too far. When he puts on a new chain, after a few cuts, his cuts start to pull. Chain after chain, this can repeat itself over and over. What is often the case is at certain speeds, the chain hits the bad bar plate or dawg bolt. The bad part usually dulls just the corners of the cutters on one side of the chain. Since the other side is still sharp, the cuts start pulling in the direction of the sharp cutters.
The message here is: When cuts pull, take a good look at the cutter teeth on the chain before you spend money on anything else. The chain will usually be the problem -- or it will guide you where to look on the saw for the problem.