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Mondo shows you how to use a PIC to control the speed of a Dremel... - "The Dremel drill fitted with a mini drill-chuck on a stand is a great setup for drilling circuit boards. The problem is that it does not do low speeds very well. My unit had a failed internal speed controller, so I just wired around it and connected it to a regulated 24 volt DC supply. This worked OK, but I would like a slower speed when drilling boards. Slowing down with a lower voltage, however, causes it to stall out completly when it begins drilling. What I needed was a circuit to actually increase power to the motor under increasing load." [via] - Link.
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Hmm.. I'm really curious though, why low speed can be preferred for drilling circuit boards? Fiberglass isn't the kind of material you want to drill or mill slowly, I get nice, sharp holes at ~10krpm, perhaps I lower it down to 6krpm when using large drill bits (like for mounting holes).
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I believe commercial PCB drills often run at 100-200k RPM's, and subjectively, carbide PCB drill bits definitely perform better at higher speeds. Then again, there's always a tradeoff between performance and noise; a dremel running at max speed is not something pleasant to put your face next to while you're lining up the board during drilling. The faster the better, to the degree that you can stand the noise. But, it sounds like this circuit is running it a lot slower than it should be run.
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Agreed, on a setup like this carbide bits at top speed are just the doctor's recipe. Too bad they're often hard to find.
As for the noise, it's not so bad with PCB's. But it never hurts to put some protective gear on.
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This is just the project I've been looking for. I have a dremel that has a bad speed control and I couldn't figure out the circuit well enough to build a new one. The current control is a definite plus as well. I'd be tempted to add variable speed control and a tachometer as well.
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