Saw Setting and Yield Strength

© Eugene Brennan

 

My bow saw blade is years old. I've cut up loads of logs and full trees with it and I sharpen it every so often (an extremely boring and tedious job, because there's probably over a hundred edges to do.) However, it was binding, because I reckoned, the faces of the teeth were worn and there was no kerf remaining. The teeth of a saw blade are alternately set to the left and right, so that they point slightly away from the blade. This gives the saw a kerf, making the width of the cut wider than the body of the blade behind the teeth so the blade doesn't bind. Without a kerf, a blade would stick in damp timber. I used a saw set tool on the blade (one of several old hand tools belonging to my grandfather) and it's working beautifully now, no problem cutting logs up to 5" thick. (Handier than taking out the chainsaw and good for upper body exercise.)

I tried using a saw set on a carpenter's hand saw once and it broke one of the teeth. So I'm wondering can only some modern saws/saw blades be used with a saw set because the teeth are so hard and the ultimate strength of the steel isn't much higher than the yield strength. I.e. once the elastic limit is reached, teeth don't deform plastically and just break? The engineering aspect of this post is that materials have a yield strength which is the max strain they can undergo elastically without permanent deformation. After that they deform plastically and don't spring back into shape. The ultimate strength, measured in units of newtons per square metre or pascals (a pressure measurement) is the point at which a material will fracture.