Getting More Life from Bandmill Blades
Question (WOODWEB Member) :
If you have wheels 30" diameter you do not have to be worried about fatigue because blades are bending around the wheels. The old books says the wheel diameter would be 1000 times the thickness of the blade, to be safe. The steel used today is better from that point of view. In my opinion the most dangerous for the blades is too high feed force caused by dull blade, wrong hook angle, blade guides far out from the log, big log diameter, to low blade tension, to small gullets.
All actions that will bend the blade hard (in the wrong direction) by the guides flanges, have to be avoided. The result of such bad handlings is that the steel in the bottom of the gullets is over stressed. If the grinding also is performed to hard, (signs of blue color in the gullets), the blade will crack/break very soon. Every point of the blade passes the guides about five times/sec. The aim point is to have the blade to cut it self-free and be so aggressive that it nearly feed itself. In such good case the blade will go straight (between the guides) through the cut and the steel in the gullets will be more happy. The alignment of the saw and how the blade tracks is also important things to take care of to give the blades a long life.
From the original questioner:
To contributor P: Where are you located and what tree species do you cut? Please tell me what blades you purchase and where, as I would love to try some.
From Contributor P:
I live in Sweden. We cut Swedish oak, Swedish spruce and pine. It is hard for me to say how your wood behaves in the saw, compared to ours. I think it is similar. The size of the logs I have been talking about here is from 15" to 25" diameter and about 15' long. The blades I have used in this and most cases is Munkfors. I have tested other brands of blade during the last years but I can't say how long they will last yet. There are blades with teeth as are much harder, still the same steel in the teeth and body (not bi-metal). That kind of blade is hard to adjust the set. The teeth are so hard it will split by the force when you want to increase the set. Bi-metal blades: easy to change the set but less good steel material to grind.
I've read books that don't have as much information as you put into your response. Well said! One other issue on the blades is the hook angle. Common angles are 10, 7, and 4 degrees. You can adjust this somewhat with the sharpening. Ten degree blades are good for softer woods, since they have a more aggressive cut, and 7 degrees seem to work well for oak. I keep a few 4 degree blades on hand for logs that have been down long enough to have dried out.
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