Light dimmers and controling the speed of power tools.

Hi all. We were discussing controlling the speed of a dremel ( high speed low torque drill ),
http://www.instructables.com/id/SRWK8Q72Y7EZBF9BUX/#CCCHJSHF1U9XVKQ

In the example of converting a sewing machine on this page, http://metku.net/index.html?path=mods/foot-pedal-mod-for-rotary-tools/index_eng the speed controller is a resistor (rheostat) and a capacitor. What is the importance of the capacitor? Does it prevent resonance? Or maybe it adjusts the power factor?
THe question really is : is there a difference between a light dimmer and a speed control ( like on a sewing machine)? When are they interchangeable.
Thanks BoomGuy
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    BoomGuy@no_spam.com writes:

You really need to know what type of motor is being used. Universal motors are quite easily controlled using series resistor or phase control (dimmer-type technology). Phase control probably gives you better control (higher torque at low speeds, and slow starting without uncontrolled jump to higher speed). A crude light dimmer might not be very good though -- something with more than the bare minimum of components for light dimming will probably do a better job and be better protected from the noise generated by the commutator.
Induction motors are harder to speed control -- you will probably need some type of inverter technology.
--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]
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On 23 May 2007 20:23:17 GMT, in alt.engineering.electrical you wrote:

Ok. Confession time:) Last week I was using one of these without a speed control with a tool ( similar to a bit ) that was not rated for that speed. The bit broke, hit me in the arm, causing me to throw the dremel into some rags on the side. The shaft got caught up in the rags and the motor blew. Now I'm debating replacing it, or getting a different model. For the money, this is the best one that I can get except for the ability to adjust speed ( plus eventually I do want to modify a sewing machine pedal as a speed control for this ).
The upshot for this is that I have a broken model and I am thinking of a getting the same model. Talking to B&D was no help. Despite lots of ads saying "compatible with most Dremel parts", they said it should never be used with any nonB&D parts. ( I hate when companies do that, and it is borderline illegal ).
HERE IS THE IMPORTANT PART. First off, the dremel is rated at 2A and spins at 30000, Since B&D is of no use I am taking apart the fried dremel for spare parts and to identify the motor. The circuitry inside is simple. there is an SPST switch ( for on and off) , there is a PCB with one small black box labeled SB604G with four pins, two are labeled S ( probably badly made ~s ) one l;abeled + and the other labeled -. On line I've identified the part as a bride rectifier. The + and - pins have leads running to the motor. The ~ leads:one runs to the 120V plug, the other runs to the switch , the other end of the switch runs to the 120V plug.
I haven't had a chance to take apart the motor fully yet, but here is what I do know. There is a metal plate wrapped around the motor. It is D65028 and 3C2844. I was unable to use this to identify the motor itself. The outside of the motor. is magnetized, but that could have happened when it fried.
I can't see much inside.yet, There are strips of carbon in a circle around a rotor on the lower half. There seem to be a pair of carbon brushes pushed up against the strips so when the motor turns the brush touched a diffe3rent strip. More when I get to take it completely apart.
I don't know much about motors, So if this helps identify the type of motor can someone please help?
BoomGuy
-- Thad
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writes:

http://cgi.ebay.com/VINTAGE-POWERSTAT-10-AMP-VARIAC-NICE-NR-L-K_W0QQitemZ280116430142QQihZ018QQcategoryZ40067QQrdZ1QQcmdZViewItem
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boomguy@no_spam.com wrote:

Do yourself a favor - buy a new Dremel tool already equipped with variable speed. It will be cheaper and safer than trying to jury rig something. If you must jury rig, you want to do it on the DC side if the bridge rectifier with PWM control.
Ed
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