Re: CNC and grounding ... and dust collection
Dave Hempy
It should go without saying (but yet I say it!) that the DC (-) ground is isolated from the chassis ground. Correct?
For your vacuum hose ground wire, does it matter which end you ground it to? Dust control end or router end?
Oh that reminds me...I bought the dust collector accessory kit from Harbor Freight last week, including 10' of flex hose. It is under the router table. Feel free to crack it open and start figuring out how hook it up. I'm pretty sure we'll need some more hose to complete it, flexible and/or rigid. We have yet to make/buy a dust shoe to fit around the router. Anyone want to find some drawings for a dust shoe we can cut ourselves and save a hundred bucks? I think there are some on Joe's forum.
-dave
-----Original Message-----
From: coll...@googlegroups.com [mailto:coll...@googlegroups.com] On Behalf Of michael culp
Sent: Monday, May 21, 2012 10:32 AM
To: coll...@googlegroups.com
Subject: CNC and grounding
I was working on my cnc this weekend and a thought occurred that I should warn you guys about, Make sure your machine and your dust control system are grounded correctly.
When we hooked up a shop vac to our cnc the static caused by it zapped me and fried our controller board. To fix this we ran a grounded wire through the hose from end to end and ensured that the computer and the power supply for the motors & their power supply were all fully grounded.
-michael
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Michael Culp
Yes ground the metal table. Yes seperate from dc ground of you can manage it and ground the hose at the vacuum end.
Michael
Sent from my iPhone
Dave
> From: Dave Hempy <DHe...@ket.org>
> Subject: Re: CNC and grounding ... and dust collection
> To: "coll...@googlegroups.com" <coll...@googlegroups.com>
> Date: Monday, May 21, 2012, 2:32 PM
>
> So we're talking about a common ground to the AC wiring ground, right? Does it
> matter if the dust control and router are on different circuits? Should this
> be tied to chassis ground? (e.g. should the steel table be tied to this ground?)
One should probably check the NEC (National Electric Code) for the final word.
I don't believe that it matters, though, if the grounds are on different circuits,
since all of the grounds are required to be tied together.
Basically, you want it so that any static, on any part, which arcs to any other
part, doesn't zap any sensitive electronic equipment. And, note that, during
machining and dust collection activities, rather incredible static voltages may be
developed (e.g., >100 KV!).
There is a concern, while machining flammable materials, that a spark/arc may ignite
the flammable materials. Has any consideration been given to fire suppression?
> It should go without saying (but yet I say it!) that the DC (-) ground is
> isolated from the chassis ground. Correct?
Good question. And, the answer is?
> For your vacuum hose ground wire, does it matter which end you ground it to?
> Dust control end or router end?
For the static/DC case, it shouldn't matter. It shouldn't be carrying very much
current, so you shouldn't have any ground loop situations. It's more of a static
bleed wire than anything.
> Oh that reminds me...I bought the dust collector accessory kit from Harbor
> Freight last week, including 10' of flex hose. It is under the router table.
> Feel free to crack it open and start figuring out how hook it up. I'm pretty
> sure we'll need some more hose to complete it, flexible and/or rigid. We have
> yet to make/buy a dust shoe to fit around the router. Anyone want to find
> some drawings for a dust shoe we can cut ourselves and save a hundred bucks?
> I think there are some on Joe's forum.
There probably needs to be a bit of instruction/caution on the subject of
dust/chip collection. I'm not exactly sure what materials are planning on
being machined/worked, but it's usually a good idea to separate the waste
streams such that differing materials are not mixed.
One incident that I'm aware of, that happened in the machine shop of a particular
military base (which I won't mention the name of!), involved steel and Aluminum
parts being machined, with the waste chips from both being dumped into a 55 gallon
drum. When the drum filled up, it was set out on the loading dock, where rain
entered it. This caused the steel/Iron to rust. Even more troubling was the fact
that the oxidation reaction of the steel was causing the drum to heat up. I pointed
out that they had just made an impromptu 600 pound Thermite bomb. Whoopsie!
http://en.wikipedia.org/wiki/Thermite
> -dave
Other Dave
Derek Eggers
2) Regarding making the dust shoe, I have a little 12" duct angles leftover that I'm happy to drop off if useful. And I have a tin cutter and rivet puller that I can bring down if it will help.
Derek Eggers
michael culp
I'm not sure that I have great response to your questions about static and grounding but I'm going to give it a shot.1) While using a shop vac in my boat hull I've been zapped several times. Shocking at first, but not so bad after a while. The static didn't seem to have a specific pattern, so I wonder if it's reasonable to run a small grounding line down the whole tube, zip=tied at several locations?