Dust Collectors...

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Lobby Dosser wrote:

I could probably do that... Isn't the wheel on top of the bit there so your wood can use it at a guide. Plunge in and push forward...
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wrote:

The incorrect idea is that by "grounding" the plastic piping, static charge can be eliminated.
When two things in contact with each other are separated, electrons can be stripped from one of them and deposited on the other. In this case, the objects are 1) the piping and 2) air/dust. If either or both of the objects are insulators then the resulting electrical charges have no place to go and thus remain in place, i.e. they are "static."
If the process is continous, as it is when air/dust is flowing through the piping, the charges continue to build. They cannot build without limit however because there is no perfect insulator so when the potential difference (voltage) becomes high enough the insulative properties will be overcome and the charge will discharge. This can happen rapidly, via a spark (think lightning) or more likely, by gradual discharge.
The myth in woodworking is that "ungrounded" piping will generate static charge buildup sufficient to create a spark inside the piping that will ignite the combustible dust. There is no documented evidence of this ever happening.
Furthermore, even if there was, there is no way to "ground" an insulator. It's an "insulator", by definition a poor conductor of electricity, and attaching a wire to it, or running a wire through it cannot prevent the buildup of charge in areas not directly in contact with the wire. The best this wire can do is to insure that the equipment at each end is at the same potential, something that should already be the case due to the equipment-grounding conductor in the power wiring.
Can you be shocked by static charge buildup in your shop? Sure. I'm in AZ where the RH can be under 10% and dry air is a better insulator than damp air. If I'm wearing rubber soled shoes and vacuum up a large volume of dust, using my all-plastic (double insulated) vac, the vacuum and I get charged up. If I then touch the metal frame of a piece of grounded equipment I will get a shock. There might even be a tiny spark. Does anyone think that this spark will ignite the dust in the air and burn down my garage?
If I turn off the vacuum and wait just a few seconds, I can touch the grounded equipment and not be shocked. This shows that the insulators are not perfect and that the charge is slowly dissipated. Note that this is a continuous process, which is why you don't get shocked every time you run a vacuum; if the charge buildup is small, for example when you're not sucking up sawdust, but just air, the charge is dissipating as fast as it is generated.
Tip: If possible (and I remember to do it) I just keep one hand on a piece of grounded equipment when I suck up a pile of stuff. Absent that, I bend over and touch the concrete floor with a bare hand before touching anything else. This dissipates the charge slowly and painlessly.
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"It gets very dry here in the midwest during the winter. This is NOT urban legend"
Here we go again. I too, live in the mid-west and have had an ungrounded plastic piped system about 20 years, no sign of static problem. We are talking home shop here, not commercial shop. A post a couple of year ago, using Gov. figures, estimated that you would have to reduce a 6" pc of Oak 4x4 to dust in about one minute to get a great enough concentration to cause an explosion.
Walt Conner
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