I've been asked a lot of questions about ducting...is PVC better than metal?Where do I get it? What fittings do I need? How do I install it. What about static?

Ok, I'm going to try to answer some of the questions here.

1. PVC vs. Metal pipe: I personally like PVC pipe for several reasons. It's usually less expensive than metal pipe, it's usually readily available from plumbing supply houses and it's easy to work with. Metal pipe has more fittings available than PVC pipe, but for our hobbyist systems, we don't need them. Only 2 fittings are really required for these systems; 6" "Y's" and 6" 45 deg elbows.
2. Designing & installing your ducting: I've included the same two layouts that I used for the Shop Layouts page. They show running the ducting in a typical shop layout. I have shown the ducting with all 45's and Y's. What you want to do is run 6" pipe as close to the machine as possible, put a blast gate where it's easy to reach, and then reduce to 4" if necessary and run flex hose for as short a run as you can. Flex hose will reduce air flow, so you want to keep it short (3-4') if you possibly can. Because hobbyist systems are designed to run one machine at a time, there is no need to reduce pipes to 5" and then 4" etc. when designing your system. Each machine will get maximum air flow if you run 6" pipe as close to it as possible. There are several machines that need two pickups on them: Table saws, Bans saws, Radial arm saws, Router tables are on the top of my list for two pickups. Usually you want to run a 6" line to them, put a blast gate, then a 6" "Y" and then reduce to two 4" lines. Several machines like a 6" jointer or a 12" - 15" planer will work with a 4" pickup. For these machines, run the 6" as close as possible and then reduce as close as possible to the machine. When you run the PVC pipe, don't glue it together (like I did on my first system). Instead, fasten each fitting with a short #6 or #8 sheet metal screw through the fitting and into the pipe. This will keep the fittings from working loose, but if you want to change your layout later, your pipe will easily come apart. There is no need to seal the joints on PVC slip fittings. They don't leak! And, if they do, it won't be enough to matter in the least. i.e. If you are sucking 1400 CFM through your pipe and it has a 1 CFM leak in it, it really won't hurt anything. Again, because you WILL take it apart later, make it easy on yourself.
3. Reducers: The one fitting that I didn't talk about in our system is the "reducer". For good air flow you need a tapered reducer that will give the air a nice smooth transition from 4" to 6" pipe. Unfortunately, these tapered fitting are hard to come by in S&D pipe. What I have done is make a flat reducer bushing out of MDF or plywood. It leaves a little ledge inside that will catch dust, but it really doesn't hurt anything other than a slight reduction in air flow. I take a short piece of 6" pipe and a short piece of 4" pipe. I trace around the inside of the 6" pipe on a piece of plywood or MDF. I put the 4" pipe in the center of that circle and trace around the outside of the 4" pipe. Then, I cut it out on a band saw. I cut through to the inside circle and cut it out. That leaves a donut with a slot in it where the band saw cut to the center. Slip this ring over a 4" pipe and put three small screws into the ring from the inside of the pipe. Then slip the ring into a 6" pipe and screw it in from the outside of the 6" pipe. Run a bead of silicone caulk around the pipes and along the slot. You can make 10 of these on a band saw in 15 minutes. It might be quick and dirty, but it will save you hours of searching for tapered fittings.
4. Static Electricity: First, if you like to read, go here: http://mywebpages.comcast.net/rodec/woodworking/articles/DC_myths.html. This is an article by Dr Rod Cole that discusses the myths surrounding static electricity and PVC pipe. In my own experience (I've been using PVC pipe in my dust collection systems since about 1990) I only have a couple of concerns. First, the wire in flex hose will take on a good static charge and if you touch it you will get a shock! This will usually occur if you are close to a flex hose that is carrying product because the product (dust) will cause the static buildup in the system. Because the wire is a conductor, it will release that charge to you if you touch it. So, I strongly recommend that you ground the wire from any flex hose. Second, there isn't much of a chance of getting a shock from plastic pipe, it's an insulator, BUT, if the pipe has a layer of grinding dust on it, or it has impurities in the inside or outside of it, these things can cause the surface of the pipe to become a conductor. Therefore, especially if you live in a dry climate, I suggest running a wire on the outside of the pipe, attaching it with short sheet metal screws every couple of feet (short screws through the pipe will help dissipate any static charge on the inside of the pipe too.) and then grounding the wire. Although I haven't had any problems with my systems, that doesn't eliminate the possibility so I would suggest that you error on the side of caution and run the ground wire.

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