Monday, September 2, 2013

Bandsaw Blade Crack Failure

In my shop I have two bandsaws.  The large 7” one hardly ever sees use any more as I no longer take on large projects.  The inexpensive small 4” one I have raised up on a stand so it is at standing working height.  It sees use every day cutting smaller stock when a need a clean and straight edge.

I use bimetal blades and go through about five per year.  I have noticed that when a blade is at the end of it’s life the saw arm developes a subtle up and down deflection which gradually increases in amplitude until the blade breaks.

The cause of the breakage is invariably a gullet crack.    Sometimes, I can find partial cracks in addition to the complete break.  I have chosen to just live with the situation rather than take the time needed for a full investigation and correction of the root cause, but for those interested here is a link to common causes of gullet cracks.

Apparently cracks also can originate on the blade back side also and here is a link to investigating those.

Loosing blades to crack propogation probably doesn’t cost me as much as making a mistake when trying to cut some tool steel stock.  I have learned to observe very carefully as the bandsaw blade starts to travel across the stock.  If chips aren’t flying off as they usually do, I stop and use my presto marker pen to write, “No bandsaw”, on the stock.  That material will need to be cut with an abrasive blade or possibly with the torch or hot cut with with a hack with my hydraulic forging press.

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