New source for chip/swarf vacuum?

[grooveguy]

Decades ago I was faced with finding a vacuum pump to pull the chip away from my hot stylus. I'd already burned-out my mom's Eureka canister vacuum and needed something to replace it... both my mom's Eureka and one for my own 'smelly experiments,' as she called the delightful aroma of freshly-cut lacquer. I finally settled on a castoff shop-vac, but on a Variac so that it could run full-throttle to grab the chip, and then at reduced capacity once the 'end of the groove' was safely into the institutional mayonnaise bottle. Cutting back the vacuum saved the motor from burning itself out because of low airflow.

Although I was satisfied with what I'd made, I nevertheless wondered if a constant-displacement pump of some sort might serve the purpose better than a high-speed fan. One idea that came to mind was use of a "smog pump," by then required in new cars on California roads. These vane-type pumps worked like many of the Gast Co. designs:
https://www.gastmfg.com/products/211/0211-103a-g8cx
(or like a Wankel engine) and develop pressure/vacuum at relatively low speeds. A smog pump from a wrecking yard was mounted and belted to some old motor kicking around, but the motor didn't have enough oomph so that idea went nowhere.

Recently, while surfing eBay pages, I came across this 21st Century version of the smog pump:
https://www.ebay.com/itm/194785825400

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These are not vane-style, constant-displacement devices, but very similar to shop-vac motors, except that they apparently have multiple stages and are meant for hard usage under the hood of a car. These can be very expensive as a factory-replacement part, but the eBay offering is obviously for DIYers who perhaps are going to sell the car shortly . Anyway I got one and hooked it across my car battery, and wow... this thing sucks! ...which is good.

With 12V across it, it draws over 10 amps, so we're talking over 100W of power required. Returning to eBay I found this power supply that ostensibly delivers 15A:
https://www.ebay.com/itm/373875046402?var=642886662240

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Well, maybe 15A in another life; it went into overload and wouldn't even start the smog pump. However, with a 0.75-ohm resistor in series, the motor did run, albeit at reduced speed, drawing about 6A with between 5 and 6 volts measured across the motor. This is an inefficient way to drop the voltage, so next I'll try making that power supply variable. A 5V, 10A supply ought to run the pump well enough for chip-sucking, but especially with polycarbonate and other static-y plastic blanks full suction might demand a better power supply and full voltage... at least at the start of a cut.

In automotive use these pumps don't run continuously, just during cold-starting and at engine idle. But the pump is of rugged design and could be housed in a soundproof box without fear of burning it out with 'throughput starvation.' Anyhow, this is just offered as an idea, an alternative to more expensive solutions perhaps.

[markrob]

I wonder can if you avoid the supply going into current limit if you short out the limiting resistor after the pump comes up to speed?

[grooveguy]

That might well work; motors always pull a hunk of power when they're stalled. Alternatively, if that supply can be made variable, it could start out at 4 to 5 volts, which will make the motor turn, and then ramp up to full, or to whatever current the 15A (HA!) supply will put out. Same goes for shorting out just part of a series resistance, too. For pulling chip, 5 to 6 volts is plenty and would allay any fears about burning out the motor with long-term use. As I understand it, these things run intermittently under the hood of a car, and at a price of $25, when a factory-replacement runs hundreds, I'd be inclined to let it loaf.

Here's another alternative:

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I've got one of these, and boy are they powerful. They're blowers, not vacuums, and can inflate an air mattress to near-bursting very quickly. The air inlet at the bottom is about the same diameter as the big end of a small kitchen funnel and could be adapted easily. A bit expensive, and I don't know how they'd hold up to continuous use (motor with brushes), but might be worth a try.