Troubleshooting a Dished Sawmill Blade
Heat build-up at the center of a circular blade can distort its shape. July 28, 2006
Question
I've been sawing cottonwood and pine with no trouble. I cut into an oak log and right away I noticed that my blade began to wander off track. I backed the log out and I saw that the blade was dished. I shut it off and the blade was rather flexible. As it cooled down, it straightened out and was rigid again. I put my hand on the hub of the blade and it was warm, but not hot. Any ideas why this happens?
Forum Responses
(Sawing and Drying Forum)
From Professor Gene Wengert, forum technical advisor:
Heat in the eye (assuming you have a circular blade) is the most common cause. Could be a piece of wood caught or bearings that are heating. Also, how sharp are the shoulders in the gullet? With oak, you probably slowed down and made fine sawdust that could spill out with dull gullets and cause heating.
From contributor J:
The sawing of a hardwood requires you to maintain saw speed, and not have a loss of rpm in the cut. My own mill can cut cedar at an idle with no problem, but when cutting hardwoods, I run at the speed where the engine is developing torque, and probably the blade is hammered at. The other thing to pay close attention to is the condition of the bits. If they are rounder on the corners, especially to the side that it is running to, then you need to sharpen the bits, preferably in the saw. Blade heating in the rim can be caused by wood rubbing at the center, but also the leading of the blade, since the "flexing" takes place toward the hub, working the blade and warming it up. The times this has happened to me, I let it cool awhile, and it always returns to correct, slightly dished shape, with the dish toward the log.
From contributor G:
When going from softwood to hardwood, I have to change the lead-in on my saw blade. On softwood I run the blade almost straight with the carriage. On hardwood I set the back of the blade 1/4 to 3/8 out on a 50" blade.
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