Does rattling mean it's broken?

Sunday, November 4, 2007 | Reader Comments | How-To | Saws

Did You Know The "Rattling Sound" From Your TS-Series Saw Means It's Working, Not Broken?

MMC Electronics

The "strange noise", often described as a rattling sound, is caused by the MMC electronics in the tachometer regulated speed control sending power to the motor in a stream of various sized bits.The motor is constantly being turned on and off to keep the saw blade rotating at a constant speed.

Most of the sound is being produced by "gear backlash" between the small pinion gear on the rotor and the larger gear that drives the saw blade. The saw blade behaves like a flywheel and has inertia that keeps it rotating while the small gear has slowed down. The opposite sides of the gear teeth tap against the mating teeth of the large gear and the vibration conducts to the saw blade, where it becomes sound which radiates from the blade like a speaker. Some of the noise is created by the field coil wires and plates vibrating from the pulsing magnetism as they energize and de-energize. These pulses get longer and longer as the saw is put under load.If the machine is run without a blade installed, there are no unusual sounds. In this case, the pulses are short, but there is no inertial resistance from the blade flywheel.

The "strange noises" heard from a Festool circular saw are normal... I would be more concerned about a saw that did not make these noises. It might be an indication that it's speed control is malfunctioning. The Festool saw is unique. If other manufacturers used similar Pulse width modulation speed control in their saws, customers would come to expect such "strange noises", and they would not be so strange. The noises would be the "familiar Festool sound".

Now that's...

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