Thread: Power tool noise

Hi,
It is the speed series wound motors run at. A router does not even have gears, it is direct drive. They run at about 20,000 to 30,000 RPM, induction motors on 50~ run at 750, 1,000, 1,500 or 3,000 RPM depending on the number of poles.
Hope that answers your question.
Regards

Look up Induction (typically machine motors) V Universal (typical Power tool motors) on Wikipedia

I concur with the above comments, but wish to expand on them.

Many of the tools with universal (high speed) motors are used for making interrupted cuts of some sort (circular saws, routers, portable planers, bench top thicknessers, drop saws, direct drive tablesaws, etc). With this, there is a short period with a tooth actively cutting material, followed by a period where the gap between the teeth is in the cut allowing dust or swarf to clear the kerf, then the next tooth engages the material being cut and the cycle continues. This is a major source of the increase in noise between the tool operating unloaded and under load.

A lot of the noise associated with universal motors is created by the need to have brushes in contact with the commutator on the armature, (at least 2 brushes and 20-30 segments on the commutator so a lot of transitions each revolution). Further noise is created by the fan needed to pump a significant amount of cooling air through the motor. If the unit has gearing in the system, (saws, grinders, polishers etc,) they will contribute a significant amount of noise also, but as mentioned, this won't happen with a router as they operate as direct drive.

Noise from power tools remind you that it is not a toy to mess with. I am very excited about the new Makita oil filled impact driver that operates at 70ish dB.

Cooling fans in tools can shift a lot of (noisy) air: in the blurb that accompanied the release of a new range of mini grinders one manufacturer recently quoted a cooling airspeed of 400km/h (over Mach 0.5!) across the windings!