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Rick Hubbard
03-24-2008, 1:19 PM
I ran into a fellow that I know only casually on Saturday at the local hardware store. I was purchasing some 4 inch pipe hangers and he asked if I was by any chance installing a DC. I wasn’t- I was just anchoring some “iffy looking” duct work, but, in any case the conversation was on. Eventually he asked me if I was using plastic duct and, if so, he wanted to come over and see how I had grounded it. I explained to him that I had NEVER grounded it and that I have virtually NO static buildup. He was incredulous, and insisted to come and look at my set-up. After I demonstrated the absence of static, he mentioned that in his shop when he uses the same identical DC I own, the static charge on the ungrounded ducting and hose is so bad he becomes frightened.

So here is the question- how can this be? It can’t be climate/humidity differences because we only live about 5 miles apart. Both our shops are stand-alone and both use propane heaters (which tend to raise humidity when in operation). It looks to me like we both used similar ducts and the total runs are about the same length. The only thing I can see that is really different is that almost every one of the tools I have are hooked to the DC are resting on cabinets with rubber casters. Could this be the reason I have never had static problems with my DC?

Jason Beam
03-24-2008, 1:28 PM
5 miles is plenty of distance for a climate difference - though it isn't likely to be major.

Dryness is the first thing I thought of. Since the laws of nature state that you can't ground an insulator, your question about the raised equipment isn't the likely reason you don't see it, either.

The reason could be simply the amount of use the system sees. I've heard stories that some folks who use PVC duct work will see the static build up quite a bit at first but eventually disappears over time. This one I don't fully understand, but one theory is that the duct gets an ultra fine layer of dust on it that eventually prevents a static build up.

It's an interesting phenomenon, for sure.

Dick Strauss
03-24-2008, 1:55 PM
Rick,
Sharp bends in the flexible DC hose will build much more charge (because of more collisions per second per sq inch) between the tubing and the wood waste. For example, most folks that have a planer with a mostly horizontal connector that connects to their overhead DC system with an almost vertical connector. This means that most folks come out of their planer and immediately make a 90 degree turn toward the ceiling to connect to the overhead DC system. This "elbow" can generate lots of static charge right where you remove the piece from the outfeed table. I've experienced this one first hand at a friend's shop.

As Jason said, dryness can definitely vary from one building to the next based on the foundation. Higher humidity makes it harder to build a good static charge. My neighbor and I might have different amounts of humidity because imperfections in the concrete or how the base was prepared before the concrete was poured, etc. We may also have different water mitigation strategies (french drains, more slope away from the building, drain tiles, etc).

I don't really have the answers not knowing the details of the two systems but am just suggesting some items to consider...


Dick

Rick Hubbard
03-24-2008, 2:21 PM
Rick,
Sharp bends in the flexible DC hose will build much more charge (because of more collisions per second per sq inch) between the tubing and the wood waste.

Hi Dick

Hmmm- this might be a key issue. I did notice that the other guy had LOTS of flex-hose running from his machines to the PVC duct, although I didn’t pay much attention to angles. By contrast, I use a very limited amount of flex hose and the relatively short runs that I DO use come off the PVC drops at 45 Degrees so that there is very little angle to the machine itself. I'll try to get some pics tonight of what I mean.

Also, now that I think about it, the location issue is probably more consequential than I first imagined. My shop is less than 100 feet from the riverbank while I don’t think someone could even see water from where the other guy is located.

Additionally, perhaps there is something to what Mr. Beam said about increased DC usage resulting in diminished static charges. I use my DC a lot, while my acquaintance is too afraid to even turn his on at all.

Thom Sturgill
03-24-2008, 3:30 PM
I have no idea whether it would make a difference, but what about the moisture content and nature of what is being cut? If Rick lives near a river, might not his wood tend to be a little higher in moisture content, and wouldn't that also affect the collision/static effect?

Jason Beam
03-24-2008, 5:41 PM
I have no idea whether it would make a difference, but what about the moisture content and nature of what is being cut? If Rick lives near a river, might not his wood tend to be a little higher in moisture content, and wouldn't that also affect the collision/static effect?

Excellent point, Thom!

The dryness of the wood shavings themselves has a substantial impact on the level of static that can be generated.

Lots of little factors at play, huh?

Adam Cavaliere
03-24-2008, 10:20 PM
I am sorry, but I am new to all of this - how bad does the static actually get? Right now I just have a long run of flexible hose running, but have been considering other options...

Jason Beam
03-24-2008, 10:33 PM
Some folks report the shock is a little jolting. That's about the only thing that'd worry me - if i had a duct running right alongside my router table or something and i inadvertently got zapped while feeding something through, it could be pretty dangerous. Otherwise, it's more of a nuisance than anything. It won't explode ... no home woodworking shop has ever exploded due to the static :)

Ken Fitzgerald
03-24-2008, 10:44 PM
I live in Lewiston Idaho. I am not wealthy. But when I installed my DC I paid the additional cost of metal pipe (snaplock) just to reduce the chances of static shock. I'm not the least bit concerned about any harm from it but we get 12" of moisture per year annual average. Frankly I don't find the shock pleasant. With a low humidity here, it only made sense to me to use metal.

Keith Outten
03-25-2008, 4:35 AM
For what it's worth I have to wrap my DC hose with a copper wire to drain off the static charge on my CNC router. Without the copper ground wire the static charge will cause the CNC machine to stop in the middle of a job sometimes as the feedback seems to affect the motors and possibly the control box.

The gound wire works, there is no static on the pipe or hose while the DC is running.

.

Rick Hubbard
03-25-2008, 7:28 AM
I am sorry, but I am new to all of this - how bad does the static actually get?

Since I have not actually seen this guy’s shop, or the DC in operation, I’m not sure how bad it gets. He did say however, that the amount of dust clinging to the ductwork when he is using his planer is “frightening.” He has stopped using his DC altogether and rolls his shop vac around when he feels it necessary to collect chips. Maybe one of these days I’ll drop by his place and see for myself what he is talking about.

The mention of moisture and its relationship to static buildup is really intriguing. I think I will invest in one of those el-cheapo hygrometers and put it in my shop to get a semi-accurate reading of just what the humidity actually is in my work area. Right at the moment, I can’t imagine that proximity to the river could make too much difference- there is still 30 inches of ice and who knows how much snow on top of that (there is over 3 feet on my lawn).

Rick

Steven Wilson
03-25-2008, 10:46 AM
I am sorry, but I am new to all of this - how bad does the static actually get? Right now I just have a long run of flexible hose running, but have been considering other options...
Well, take the shock you get by rubbing your feet on carpet and then touch a door knob and multiply that by 5-10. It won't kill you but it can be a rather nasty shock. Overtime, the static will attract enough dust to land on your piping so that you may not get shocked. However, letting dust build up on your DC piping is a fire hazard. Wraping a wire on the outside of plastic ductwork will minimize the static or just use metal which doesn't have the problem at all.