Breaking bandsaw blade

Occasionally on this forum or ones like it we see a post from somebody who says "My bandsaw blade has a kink in it. How do I straighten it out?" On further dialogue, it turns out that the kink is front-to-back, not side-to-side. The answer to the poster's question is that he should buy a new blade, because the old one is breaking. I caught a blade doing this, and took a picture to show folks who haven't happened to see this.

What is happening is that the blade is work-hardening. Eventually the work-hardening causes a stress crack across the blade. When the crack crosses the blade partway, the blade is continuous only on one edge, but not on the other. However, it is still being stretched over the wheel at both the front and the back, so it kinks at the crack. While it is on the saw, the stress crack is very fine, and very difficult to see. I found this one only because I could see where the kink occurred. For the photo, I coiled the blade up, which acted to open the crack.

To give you a sense of scale, this blade is 3/4", 2 TPI.

often on blades that were improperly annealed after welding. They were just too brittle to begin with. You mentioned work hardening during use. I would venture to say (from years of experience) that 99% of the time it had everything to do with the quality of the weld/annealing process. You blade was a crack waiting to happen. Even the best band-saw blade suppliers let them slip by occasionally. If you have access to a blade welder you can easily reclaim you blade.

Jamie

Thank you for the info, it makes a whole lot of sense!

After having a woodmizer mill for ten years, [since sold] whether the weld or anyplace in the blade that develops a crack, which usually starts in the bottom of the gullet of the tooth, is caused by stress.

Now if I had a weld to break, I always questioned whether it was actually a bad weld, or stress.
I went through the process of having a few blades that broke in the weld, rewelded. But soon found that all I accomplished was, the blade was a 1/4" shorter, and it soon broke in another place.

I normally got 4-6 sharpenings on my blades before they broke.
I sharpened my own, as well as for a few others.
These were 1-1/4"x7/8"TPI blades.