Troubleshooting a Bowed Bandmill Cut

Blade problems cause a bandsaw mill cut to curve downward. August 29, 2006

My first cutting problem has occurred, two years after I built my mill. Never experienced this before except with a terrible knot in oak. I recently changed the guides with larger diameter bearings.

The mill cuts straight down the log on both sides. At the entry it cuts straight between the guides. The cut starts to bow downward (concave) between the guides, the farther I cut down the log.

I'm thinking my blade is pointing downward, but the guides keep the cut straight. Anyone have this problem before?

Forum Responses
(Sawing and Drying Forum)
From contributor R:
I'm sure you have a blade problem, not a mill problem. I've had this problem with saws that were not correctly set, i.e. more set on one side. You should check out the folks at Suffolk Machinery. They have great troubleshooting info.

From contributor T:
Had same problem… Determined my guides, which are on both top and bottom of blade, were changing set on blade. Changed guides, reset set on blades and okay now.

From contributor H:
Looks like a blade problem to me.

From contributor A:
Probably blade. Check your saw tracking on the wheels. If the blade is sitting too far back or is too narrow after many sharpenings, the set on the side of the blade that rides the wheel will start to straighten, so the other side will walk in the cut, thus the downward movement. If so, the more you cut with that blade, the worse the problem will get. Adjust the tracking to get the gullets off the wheel.

From the original questioner:
It was a new blade from Suffolk Saw and I always have good cuts from their blades. I'll change the blade this evening with another new blade and go from there. Thank you.

From contributor A:
Doesn't matter how new the blade is. If the point of the tooth is riding on the wheel, the teeth will straighten. Will also straighten quicker if the belts are hard. The bottom of the gullet should be 3/16 or more from contact with the wheel. If not, adjust the tracking to move the gullet away from the wheel.

From contributor A:
Actually, contributor T had a similar problem, except the guide rollers were doing it. Regardless, if you check the set on the blade in question, you will probably find that it differs, side to side. The inside set will be straighter (or less) than the outside set.

From contributor D:
Just another thought. I had this trouble with the first mill I owned. Turned out that the blade tension was too low. Upped the blade tension and I was fine. Not sure how you monitor blade tension on your homemade mill, but if the blade and roller guide inspections doesn't yield anything, I'd check this next.

From the original questioner:
It was a bad new blade. After I put another new blade on, it cut like a laser. I'll give you all an "A"! Thank you.