Why Do Saw Blades Scream

 It does not happen very often.  Nobody likes it.  It really is not anybody’s fault, but some saw blades just scream on some machines.

 Sometimes a good saw shop can retention the blade and solve the problems.  Maybe once every year or two we sell a blade that screams and we just replace them.

Good saw blades are tensioned so that they run straight and true.  In saw blades the inside and the outside a blade run at the same rpm but the outside covers a lot more distance so it runs faster.  This gives the blade a tendency to curl over which is highly undesirable for a variety of reasons.  A tensioned blade will use the inherent and/or induced tension in the steel to counter the tendency to curl over.

Because of the quality of the steel and the tension, they behave somewhat like a tuning fork.  As hard as the industry tries it is so far impossible to make every blade identical.  Currently, the state-of-the-art is at a level where the problem is that no two pieces of steel are identical just as no two places in the same piece of steel are identical.

Every machine is slightly different.  Every machine has a different vibrational frequency no matter how slight.

When the right blade is put on the right machine then you get screaming because the frequency of the blade matches the frequency of the machine.

You can change the frequency of the sawblade with slits or slots or scrollwork or copper plugs at the end of the expansion slots and that may work.

You can change the frequency of the machine.  About the only practical way to change, the frequency of the machine is by altering the shape of the blade guard.  Some guards actually have a little sliding door in them somewhere.  Typically, the operator has no idea what the door is for.

One way to test this is to remove the saw guard, run the machine, and see what the noise level is.  This is purely for testing.  You do not want to run the machine without a guard for any reason.  Running this particular test can give the operator the idea that running the machine without a guard is a good idea.

Saw blades have critical speeds.  When a saw blade hits a critical speed, it wobbles.  Sometimes it is just a plain wobble.  Sometimes it is a more complicated wobble and this is called ‘potato chipping’ because the blade sort of looks like a potato chip in slow motion.  Once you get past the critical speed, the blade straightens out until you hit the next critical speed.

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