Why a Circular Saw Blade Cracks

There are numerous reasons why a circular saw blade will crack, or rip, at the shoulder.  The most difficult part is determining with certainty the reason for a specific application.

When independent labs have analyzed the steel and performed a failure analysis the reason given in almost every case is “metal fatigue”.  It is a phrase open to some interpretation.  The steel in a circular saw blade will eventually wear out and be useless.  It can only handle so much stress.    Variables that have an impact on the life of the steel are:

 ·         Sharpness of the tool – Are the blades pulled out of service before or after they get dull?

·         Impact or force being applied to the body in its application.

·         Machine alignment.

·         Species of wood (or type of metal, plastic, etc) being cut.

·         How well was the carbide brazed?  There are many subsets to this topic which include critical temperature of the steel & how well the steel was annealed.

·         Gullet capacity issues.

·         Proper hardening and tempering of the saw plate.  In short, is the plate the proper hardness and does it have the proper martensitic structure?

Quite often it is hard to gather all of the information needed to make a determination with any certainty.  That being said, most of the items mentioned above can fall under “metal fatigue”, it’s just a different method of wearing down the steel until it can no longer handle the demands of the job.

Metal fatigue doesn’t always result in cracking, either.  New saws can be used in many cases for at least an eight hour shift in sawmill gang application.  Blades will hold tension for this period, run true and lumber deviation will remain consistent.  As the bodies get past their useful life they may begin to lose tension after a period of 4-5 hours.  At this point the mill may see greater deviations in their product toward the end of the shift.

Special thanks to Steve for providing this information.

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