how to bypass dremel tool internal variable speed control?

I'm on my second electronic variable speed control inside my Dremel model 395 tool. This one just crapped out with the same temperamental
symptoms as the last one. I need to use the tool tomorrow night, and would like to bypass the internal variable speed circuitry to simplify it; maybe buy an external control later.
There aren't any wiring diagrams I could find on the Dremel site. I'm thinking if I had one for the model 275 tool (single speed) and the 395 (electronic variable speed), I might be able to make the 395 into a 275 by just jumpering some wires. I'll probaqbly need to at least retain the variable speed assembly, since the brushes fit into it.
Can anyone help?
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snipped-for-privacy@emailaccount.com wrote:

Obvious, it's junk! Buy a new model dremel. or better yet, by one of those no name brands like I did, looks like it's made in the same place but cost much less! $29.00 for a complete set of cutters, stones with variable speed unit. I think it was "All Trade" or "TradeAll" or something like that.
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snipped-for-privacy@emailaccount.com wrote:

Hi
Just take it apart, I'm pretty sure it's just a "potentiometer" (variable resistor) so it would only have 3 leads, one from the external wire to the pot., one from the pot to the motor, and one from the other external wire to the other lead of the motor.
Cut things off, plug the external leads directly to the motor.
You can make yourself something that would do the same with a variable light controller (those you have to control your house lights) Get one of these, one wall plug unit and one extension cord.
PWR IN (1) to VARIABLE (1) VARIABLE (2) to PWR OUT (1) PWR IN (2) to PWR OUT (2)
it would be an awesome idea to tape everything together to cover the connections once you're done so you don't get shocked everytime you want to slow it down or speed it up :)
Have fun
(PS I also have one of the new Dremel units and it smokes too ... Uh.)
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Unfortuantely it doesn't seem that simple. The speed control has what looks like a some kind of semiconductor/IC (3 leads), a diode, and maybe a fixed resistor in addition to the slide pot. I don't know if they're doing pulse width modulation or what.
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snipped-for-privacy@emailaccount.com wrote:

I doubt they have put a stepper motor in there, they wouldn't sell for 20$ each! -- You still should only have two leads coming out of the motor. Confirm?
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Claude Desjardins wrote:

Btw you said there was a IC ... how many pins does it has, can u give out the ID (in case it's a bridge or something so your motor would be DC (Uhm?!) and wouldnt be a great idea to plug it right into a wall outlet!
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Claude Desjardins wrote:

Every Dremel tool I've had apart used a universal motor, and the speed control was a simple dimmer circuit. This one might be PWM, and run the motor on DC.
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Michael A. Terrell wrote:

Most of the cordless drills these days use PWM power FeT drivers.
I modified a cordless drill with a mini PIC and Bridge to perform regulated torque control, auto reverse and then forward again until maximum torque was no longer peaking. Did this so that the drill would have a TAP mode in it. I stuck a mini pot on the back side of the handle to set the torque level.
if his dremel is also cordless, It may also be using it a PWM? who knows. how ever, with the part count, I'm guessing he's using a corded unit with a phase control.
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Jamie wrote:

None of those I've seen used an IC in the speed control. Also, he didn't mention a filter capacitor, so id may be a simple dimmer circuit. It's hard to tell from such a vague description. Part numbers would have been a big help.
BTW, have you seen the small DC powered clone at Harbor Freight? It runs on 12 VDC, and comes with an AC adapter. I was thinking about using one (or more, with different sized drills) with a homebrew CNC machine to drill PC boards.
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Michael A. Terrell wrote:

Hmm, No, I haven't checked into Harbor Freight in some time how ever, I think you'll find that a lot of named brand tools we know are now being made by the same people that make the no-name brands from China. For example, I have a rotary tool that in all respects is a dremal. bu t the name isn't of course. As far as drills with PWM, the Craftsman 1/2 drive chuck cordless uses PWM driver board which is mounted as part of the trigger. the speed pot slider is on the board. It employs an IC chip with a logic level Power Fet.
We have some electric real movers that are still being modified by the manufacturer because they can't seem to get one to last any longer than 2 months in our shop. First they had drive problems where it wouldn't start half the time. This was an elaborate board with a micro driving what looked like a Mosfet H-bridge.
Any ways, we sent them back, the next set that came our way, they modified with the speed control in the handle of the unit. All they did was employ a speed control trigger slide switch from some existing cordless drill system. Those were very simply units, a single Power Fet with a 555 timer driving it. Not sure if it was variable freq pulsed or PWM? Anyways, those have a switch in the slide that initially connected the + batt lead to the Vcc and Drain of the Powerfet. the Minimum speed was too much on initial start. Those would burned them self's up in the switch.! oh well, so much for engineering.
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Michael A. Terrell wrote:

I took a look at google images for his model and the dimmer really is just a dimmer ... providing they sell brushes kits (2) for his model, the principle was ok from the first post; plug it right to the input.
If the person who originally posted the question still follows the discussion; it is strongly suggested that you do NOT use the tool wired that way for too long as the motor will overheat and break (or some of its internals will melt down)... take it as a temporary fix only.
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On Mon, 10 Sep 2007 21:39:17 -0400, Claude Desjardins

Or do like I did. I took a 600 watt dimmer and put it in a project box with a cord on one end, and a receptacle on the other. I use it to control the speed of dremel type tools (anything with universal motor under about 400 watts) and to regulate output of my soldering iron. Also comes in handy to dim the occaisional lamp.
As long as you don't run it wide open for long periods of time it will last as long as if you had the built-in speed control. My luck with Dremels has been terrible. The cheap chinese crap lasts just as long, for 1/4 the price. Much as I hate chinese crap.
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clare at snyder.on.ca wrote:

I was like that once - long ago.
Then I got my first DIE GRINDER!
OOOOOoooohhhh Baby.
Atomic powered Dremel.
What a TOOL to have in hand. Oh, The POWER!
But warning - this dude ain't for balsa wood, kiddies.
And you probably outta practice on something else before trimming those gnarly toe nails...
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On Tue, 11 Sep 2007 01:38:45 -0500, cavelamb himself

I've got a good air powered one of those for the "serious stuff" but the crappy dremels don't even stund up th the "balsa and toenails" type jobs.
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clare at snyder.on.ca wrote:

Well, balsa is no problem, byt dam, Clare, those toenails....
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cavelamb himself wrote:

Pneumatic rotary tool at 120psi, should fix a stereo in a matter of seconds ;) It's a "I fixed it, now go back to radioshack"
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On Mon, 10 Sep 2007 23:01:45 -0400, clare at snyder.on.ca wrote:
<snip>

More China crap...
You can get a Router Speed Control from Harbor Freight for ~$13 on sale pretty often.
"ROUTER SPEED CONTROL
Get better results and longer bit life when routing tough woods, plastics, even aluminum. Plug your router into the control unit and you instantly have a variable-speed tool. Works with any universal AC/DC brush type motor, 15 amps and under. Will not work with soft- or slow-start motors.
ITEM 43060-1VGA"
See:
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?ItemnumberC060
I have one and it works okay with my die grinder, drill, table saw (cheapo, has universal motor), 4 inch angle grinder...
Your going to have a hard time building one cheaper than this and have it look and work as well.
--
Leon Fisk
Grand Rapids MI/Zone 5b
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On Tue, 11 Sep 2007 16:44:37 -0400, Leon Fisk

Built mine about 15 or more years ago in a $2 surplus project box, using the cord from an old iron and the receptacle from an old stove-top with a dimmer I picked up in a box of stuff at an auction. I think total cast was $5 or less and it STILL looks and works just fine.
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wrote:

I have one of those HF pseudo-dremels. Not very torque-y at all. Bogs down very easily. A very light touch is required.
Jerry
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Plus the collets are brass and wear out in no time. Good for a one or two time use project, no substitute for a pneumatic die grinder. Bearings suck on them, too. Whadda ya want for $6 anyway? Spend a couple of bucks more and get the mini-pneumatic die grinder. Some of the ones I have accept Foredom collets, too.
Stan
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