Variable-speed routers

I'm taking a woodworking class right now in Chicago. I'd classify myself as an intermediate-level woodworker, but am taking this class mostly to learn something about hand tools. While everything we have done to this point has been with mallet, chisel, and saw, we discuss other aspects of woodworking, including power tools. The instructor (a gentleman with an extensive woodworking background starting as a German apprentice 30 or more years ago) commented on his dislike for variable-speed routers. His opinion is that because the variable-speed works by reducing the voltage to the motor, that frequent running of the router at a speed other than the full speed has the long-term effect of damaging the motor, at least with the class of router they have, which is a P-C probably not dissimilar to my 8529. I'd like to know what informed wreck'ers think of that.
todd
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todd said:

The routers I have which are variable speed use PWM to control the motor speed, not harmful at all, and increases torque at low speeds - and are designed to operate that way.
The add-on router speed controller boxes, from what I have seen, are nothing but light dimmers in a box. They could conceivably damage a motor not designed for their use - especially from the cooling aspect.
Greg G.
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Universal motors are designed to be run at varying voltages (hence, the "universal"). They can also run on AC or DC. At lower voltages, they draw less power.
Induction motors (as found in larger power tools, like table saws) must be run at the right voltage and frequency (AC only) or they can be damaged. At lower voltages, they draw *more* power.
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Bull-dunkie to the professor. Some wide bits need slower speed. A variable speed router can give you that. AN external speed control is poor to bad substitute. He is wrong. QED
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I'm aware that large bits should be spun slower and that that is the idea of having a VS router. However, contrary to your "QED", you've said nothing to indicate why the VS control in an average router is not harmful. Someone else posted that his router uses PWM (pulse-width modulation from what I can find out) to vary the speed. If you want to tell me that this, in addition to universal motors, is what all routers use, you'd go a lot farther to proving your assertion. Obviously, I'm dubious to his claim myself, or I wouldn't have posted the question. But if I decide to bring it up with him, I'd like something more than "He is wrong" from JLucas to back it up.
todd
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todd wrote:

Why not ask the various manufacturers? They are the ones that would have to handle warranty work.
Several of my routers have built-in speed controls. So far, none of them has had any problems.
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In fact, I have done so with Porter-Cable. I'm awaiting a response.
todd
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