In my prior blog I focused on vibration causing the blade tips to change positing as it goes thru the kert. In this blog, I want to focus on the "run out" of the blade.
How many times have you tested the "run out" of your blade? Would you believe that most brand new blades have over 0.010" of "run out" or TIR, "total indicator reading". Most blade manufacturers start with reasonably flat plate stock. Due to the fact that "cold rolled steel" has built up stresses, when the blade is cut out, many of these stresses are relieved allowing the blade to warp. This means that the blade tips will not always go thru the kerf in the same position. The spinning of a blade that starts out with "run out", creates its own white noise. It is like a car tire that might be balanced, but is out of round. It is still going to give you a rough ride.
There are a few companies who "true" their blades before the final sharpening. It is not easy to "true" a blade because you have to bend the blade to the point of "yield" before you get in into a new permanent position. I have watched this being done and was very surprised how much force and how far the blade had to be bent in order to "true" it. The saw blade behaves like a spring that always comes back to its original position when stretched or compressed. To lengthen or shorten a spring, you need to stretch or compress the spring beyond its yield point. A key property of high performance steel is that it has a very high "yield" while all steel has the same modulus of elasticity as mentioned in a prior blog.
The next time you purchase a new blade or get a used one resharpened, make sure that they "true" the blade and tell you how much run out that it has. It is very difficult to get the blade run out down to zero, but you should expect is to be at least below 0.005" TIR.
How many times have you tested the "run out" of your blade? Would you believe that most brand new blades have over 0.010" of "run out" or TIR, "total indicator reading". Most blade manufacturers start with reasonably flat plate stock. Due to the fact that "cold rolled steel" has built up stresses, when the blade is cut out, many of these stresses are relieved allowing the blade to warp. This means that the blade tips will not always go thru the kerf in the same position. The spinning of a blade that starts out with "run out", creates its own white noise. It is like a car tire that might be balanced, but is out of round. It is still going to give you a rough ride.
There are a few companies who "true" their blades before the final sharpening. It is not easy to "true" a blade because you have to bend the blade to the point of "yield" before you get in into a new permanent position. I have watched this being done and was very surprised how much force and how far the blade had to be bent in order to "true" it. The saw blade behaves like a spring that always comes back to its original position when stretched or compressed. To lengthen or shorten a spring, you need to stretch or compress the spring beyond its yield point. A key property of high performance steel is that it has a very high "yield" while all steel has the same modulus of elasticity as mentioned in a prior blog.
The next time you purchase a new blade or get a used one resharpened, make sure that they "true" the blade and tell you how much run out that it has. It is very difficult to get the blade run out down to zero, but you should expect is to be at least below 0.005" TIR.
