Installing a short amount of 4” rigid ducting with a few blast gates to a table saw, thickness planner, and drill press. What is the latest and greatest material of choice? PVC, metal, some type of clear tubing, etc?
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Metal. https://www.oneida-air.com/dust-collectors
Thank you. Very helpful!
Metal is the best material but not home center snap lock duct material. Quality ductwork sold by Oneida or similar sources is what should be used if cost is no object. HVAC distributor spiral metal duct is also a good choice and often cheaper than that sold through wood working outlets.
That said my ducting is green drainage pvc pipe but I did wrap it with bare copper to drain some static charge just incase, but that concern is debated and may depend upon your local climate. Static electricity is probably more of a concern in a dry arid locale than the pacific northwest. Standard sch 40 pvc is more expensive and can be problematic with common dust collection fittings because of differences in diameters.
I used the same PVC drain pipe as Esch. Installed it about 30 years ago. It was cheap and readily available. Before I did it, there was an article in FWW advising to ground the pipe by running bare copper wire along the outside, with sheet metal screws every 4-6 inches, holding the wire and penetrating the pipe at least a bit (the pipe itself acts as an insulator to keep the static charge inside it.)
I have a friend who owns a sawmill/planing mill. He started with metal ducting, and got tired of it wearing out, so switched to plastic pipe, which he says lasts much longer (in fact, I don't think, from what he said, that it has ever worn out on him.)
With the plastic blast gates, the groove that the gate runs in tends to get clogged up with dust, making it impossible to close all the way. We learned to orient the gate with the gate opening downward when possible, and to close it with the system still running, to pull any dust out of the groove. We also drilled small holes in the corners of the groove where the gate closes, so we could blow the area out with compressed air. I don't know if the metal gates avoid this problem, but I suspect that they do. If any gates try to fall down and open when the system is off, we make a giant rubber band from a strip of old inner tube to hold it up. For flexibility in case of machinery changes, we used very little glue when installing the system. We made sure that the joints had at least one of the grounding screws thru them, to secure them. We also taped any joints that indicated a tendency to leak (which were few.)
By the way, the plastic pipe is also much quieter than the metal.
I am also using drain PVC from the garden section. I have also added a ground wire but, I have metal blast gates. The ground wire just goes to the gates at every machine and also to the metal garage can used as a separator.
4 inch pvc is best. You DO NOT need to ground it. It is plastic. It does not transmit the charge. It is impossible to create the conditions required for an explosion in a home workshop.
I use plastic blast gates but cut just enough off them that the gate pushes dust out, which is very effective. Yes I lose a tiny bit of suction. Maybe it makes a difference. I've never noticed - the benefit of having gates that always close properly far outweighs the small loss anyway.
I don't glue my pipe fittings. Just a push fit is enough and a small screw to secure where needed.
I would not be totally dismissive of the need to ground the pvc, although I think the odds are in ones favor, but I think it depends on several factors, how dry the air is, the size and type of dust collector you have and others. If you are using a typical 1½hp 1000 cfm in a humid environment you would probably be fine. On the other hand if you were using one of the new Oneida high static pressure units which has vacuum like suction and high speed air movement in the Mojave Desert you could have a problem. I will tell you from my personal experience there is a fine layer of dust around my ductwork after several years of use... Everywhere except for about an inch on either side of the grounding wire.
Another point is while yes, a dust explosion from a static charge is not high on my list of concerns in my shop, I also don't want to be suffering a static shock every time I touch my blast gates or ductwork and there is always the risk that such a spark could ignite solvent vapors that are often present in shops.
So for the little bit of trouble it is to wrap a pipe with bare copper wire I recommend you do it.
Interestingly, the humidity is of very low relevance in terms of the risk of explosion, and the high suction power actually reduces the risk as it's even harder to get the necessary proportions of very fine sanding dust and air for an explosion to happen. Air and wood dust are only explosive in a very precise mixture - too much of either and you get no bang.
The only circumstance where this might occur in a home shop would be if cleaning up large piles of sanding dust - I can't recall the exact amounts but you need something like 1 pound of dust per minute (shavings won't explode so planers are safe) and I don't know any home shop machine capable of that.
Earthing really does not stop the static issue (which is pretty trivial anyway) as being an insulator, charge is not transmitted through the plastic, so although it may be reduced very slightly in the region of any conductors, it will be the same as it would have been anyway right next to it - as a good example, you are able to induce a static charge on a polyester sweater simply by removing it, yet you are still connected to it. Ditto a balloon rubbed on your hair. The charges in these are static and remain local as transmission through the plastic is very slow. You yourself have noticed this - your grounding wire removes the charge only in the immediate vicinity of the wire. Everywhere else you have the same static build up.
Wrapping with copper wire is of course harmless, but it is also pointless, as you have demonstrated!
Not directly related and has nothing to do with dust collection.
Over the summer I installed, sanded and finished new floors at my daughter's house. Solid birch. I used a random orbit floor sander with 4 6-inch discs, because the floor was new.
They had a fireplace going outside, and I took the dust collection bag and emtied it on the fire. I've never seen such a fireball. There was likely 4 pounds of sanding dust, and it went up in one big whoosh.
Yes, I knew dust was flammable, and I'll never be doing that again. But it was a stark lesson.
So, no fire of any kind in a woodshop. Period. And no, I don't think dust collection duct can start a fire or explosion.
Rob_SS I have hesitated to reply to this because I generally respect and agree with your opinions but when it comes to understanding static electricity you are simply wrong on most of your points.
Before I get into the details; I will agree that the likelihood of a home shop dust collector having an explosion due to static charge is very low. That doesn't change my feeling that plastic duct systems should be grounded.
Regarding the value in grounding (earthing as you call it) in removing static charge, it absolutely does, which is why when I assemble a computer it is done on a anti-static mat that is connected to an earth ground to drain off static electricity as is the anti-static wrist strap I wear. Your argument that the fact that my pipe has dust on it everywhere except for the area around the wire proves your point actually proves mine. To understand that you need to understand how electricity works and the difference between conductors and insulators. First off electricity doesn't flow through anything, it isn't like water flowing through a pipe it flows on the surface of things. The difference between a copper wire and a piece of PVC is electrons move freely on the copper surface like skates on ice while the PVC is like trying to skate on the beach. So what ends up happening is the electric charge builds on the surface of PVC because it can't flow anywhere and is called static. On a copper wire the electric charge is merrily skating along and is called current. The static charge wants to get to ground but can't because of the resistance so it just keeps building up on the surface of the PVC until it has enough potential energy to overcome the resistance and bridge a gap to ground. This is when the sparks fly and things can get painful. What my simple copper wire wrapped around my duct does is provide an easy way for the static charge to bridge the gap to ground for all those electrons stuck on the surface of the PVC. So as soon as the build up of potential energy is great enough the electrons leave to ground and keep the potential energy level along the PVC to reasonable painless and safe levels. In essence it works like the spillway of a dam, if the water builds up past a certain point it simply flows over rather than bursting the dam.
It has taken way too long to type this so I hope you are willing to take the word of a man who once, a very long time ago, studied electrical engineering (I do confess most of the brain cells that held that info died many years ago), that fast moving dry air does transfer electrons to the PVC surface at a much faster rate than slow moving humid air. If not there is always Google.
Thanks - I will bow to your greater experience - my training is medical, just with a strong interest in theoretical physics.
I am of course in the n of 1 trial state where despite using my DC for reasonably long periods of time, I've never noticed a static build-up despite being in a pretty dry climate. You are quite right of course that air transfers electrons and you get a build up on plastic. Ditto round air duct outlets. It is simply unable to concentrate sufficiently to cause a spark internally.
I too sometimes use antistatic precautions for electronics - this though is because static voltages are sufficient to break down CMOS chips - generally I don't bother unless the item is expensive though, as experience suggests zorching is actually quite rare - I've certainly never had it happen to any chip I've been using, but unlike pvc pipe explosions there is both credible science and reports of it actually happening.
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Article about fires in a commercial dust collector:
https://www.woodworkingnetwork.com/news/woodworking-industry-news/dust-collector-explodes-lumber-company-four-months-after-catching
Metal is the “best” material is you’re pockets are deep and you’ve bought the hype.
And static in PVC is real. I’ve never gotten a bad enough shock to bother me.
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