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i was just looking at another thread that talks of using "router speed controller" for controlling a heating blanket. i am curious, 1)what is the purpose of running a router at less than full speeds, 2)i thought running an electric motor on low voltage was harmful to the motor, and 3)could i use a 10 amp variac to control my router if i want to? i love the idea of slowing it down a bit, the thing really rips
i assumed the router controller is the same as a variac, but, it (the Grizzly)looks a lot smaller, and yet it can handle double the amperage? how does that work......

Slower speed for larger bits.

A router speed controller isn't a lowered voltage like a variable resistor. This works by sending full voltage in timed pulse. You use this to match a cutting speed to a feed rate. Assuming that faster is better is not always correct. Some woods will burn at higher speeds than others.

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

Many modern routers are "soft start". A speed controller won't work with them.

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wow i didn't know you could "pulse" power to an electric motor. interesting. i definitely won't use the variac then. my router is not modern, and not soft start. definitely burns wood too, but i attributed that to bad technique and possibly dull bits, though they have never seen much use. only thing i ever really use it for is to round over edges on electric guitar bodies, which is probably a "full speed" application anyway.
i acquired a heater controller a few years ago, and it switches on and off and pulses power. but it is slowwww pulses...

Many motor controllers use something called pulse width modulation. Motors run most effectively (power and efficiency) at a particular voltage so what you want to do is send in a pulses of a particular voltage into the motor. The more frequent and longer the pulses, the average energy it receives is greater, thus making the motor spin faster while maintaining power and efficiency.

Things you learn paying a school $100k over 4 years to learn and then end up using Powerpoint and Outlook for the rest of your career... lol!

A simple motor controller would probably help out your router issues before sharper bits, but I can't say that about bad technique.