I was all set up to hang 4 inch PVC in my new shop to run the dust collection through based on the recent FWW article. Recently I saw this letter to the editor from the head of Oneida saying very politely that the author of the article was all wet and PVC is a fire hazard.
Any one out there with experience with PVC as dust collector pipe?
Where can I get the cheapest steel pipe. I need about 60 feet.
Thanks
Frank
Replies
I believe the reason plastic pipe (of most any kind) is a fire hazard is the risk of building up static electricity and the potential for an explosion from the fine wood dust. The trick is to get it grounded, and grounding platic pipe is more difficult than metal.
When I build my new shop I intend to use plain old heating sheetmetal pipe that's available from most home supply places like Lowe's or Home Depot. It's easily grounded, comes knocked down (you have to snap it together which isn't a big chore), there are plenty of cheap fittings available, and so forth. Unless someone knows of a good reason I shouldn't use it.
[email protected]
I read the book by Sandor Nagy... (not gonna try and spell his name from memory) about dust in the shop. He pretty much stated that PVC is okay if it's grounded properly. If you choose to go with heating pipe, make sure it's the heavier guage so it doesn't collapse on itself when the dust collector is turned on.
Michael
As long as you properly ground the PVC (single continuous strand inside, wrapped exterior) you should have no problem. I've seen several scientific studies over the years that support this. I didn't read "Mr." Onieda's response - did he present any independent studies?
Additionally, I'm a woodworker using a PVC system, I know of several other workers using PVC (and metal), and guess what - I don't know ANYONE that's ever had a problem with either.
How did you mount the ground wire to the inside of the PVC pipe? Did you just run it through and let it lay where it may? I would think that it would be necessary to at least attach the leading, upstream, end just downstream of each blast gate. Does this wire contribute to clogging?
I have a few hundred feet of 4" PVC and had planned to use it for a future dust collection system but never could figure out how to ground it properly. I was planning on using an external main wire connected to tails about 4' oc. These tails would penetrate the wall of the pipe at a very acute angle pointing downstream and extend into the pipe for about 12". I wonder if the air/chip velocity would cause these tails to whip around and eventually break off. Don't want pieces of wire running through the blower.
I am getting to the point where I think that I am trying to teach a pig to sing (using free PVC) when want I should do is to get myself a canary (buy metal).
Well, long story, but -
My shop has it's own breaker box and the box has its own ground rod installed. Make sure a ground wire is run to each outlet and is well connected inside the outlet box and that the DC outlet ground is well grounded to the case of the DC. Then, just string a strand of #12 bare copper wire through each duct and terminate to the metal case of the DC. At each blast gate, your can drill a small hole, bring the wire out, then back into the pipe on the other side of the gate. Or, just let it run through the blast gate with negligible leakage.
PlaneWood by Mike_in_KatyPlaneWood
I ran it through the PVC and pigtailed around the blast gates and at the wye's as you depict. My dust collector is an older 3/4 hp Grizzly that is undersized for even my small 12 x 18 shop. I did experience problems with the internal ground wire clogging my furthest run, so I pulled it and ran it around the outside of the PVC. When I get a chance I will get a dust collector which is properly sized - 1 1/2hp minimum and replace all plastic blast gates with metal (half my plastic ones clog).
I also had trouble with clogs with the ground inside the pipe. I spiraled the ground around the outside of the PVC and haven't had any more trouble. Jim
If you read his letter carefully, you'll see that he says "it may be fine for the small shop" or something to that effect.
The reply to the article basically stated that PVC is not a good choice for dust collection primarily because of the small diameter of pipe, short radius elbows and T's. A common assumption is to use 4" diameter pipe to the tool based on the port size of the tool. Although the risk of fire is small it could happen. Your chances of getting a static shock are much more likely.
Many tool manufacturers do not design their ports to be used with a centralized dust collection system, they assume you will be using a single stage unit that you move from tool to tool.
You need to determine the CFM requirement at the tool. You can use 4" to tools like a small band saw or jointer but you could have problems with a 15" or 20" planer, table saw, drum sander etc.
With a centralized dust collector you need to maintain volume and velocity to convey the particulate. If you use to small of a diameter you will not be able to pull the chips or shavings from the tool because there is not enough air. If you use to large of a diameter you may not be able to lift the dust.
Most average size tools should have a 5" diameter duct to the tool. If the port is 4" you would reduce at the tool. A dust collector should have a velocity of 4,000 - 4,500 feet per minute at the tool. That said, 4" will move approx. 350-400 cfm at that velocity and 5" will move 550-615 cfm.
If anyone is interested in reading our test results comparing 4" pvc to 5" galvanized you can see it at http://www.oneida-air.com/news.htm.
I am not trying to sell anyone anything by posting here. I am only trying to help you understand why we recommend metal duct over PVC. If PVC was safe and available with the right fittings and diameters we would recommend it but that is not the situation. Think about this for a moment, If PVC was a safe and properly sized wouldn't the PVC manufacturers be doing more to promote it's use in the woodworking industry?
Of the most popular single stage dust collection systems (delta, jet, Grizzly) that are available, Grizzly has the best prices. Does anyone now of any disadvantages to purchasing Grizzly? One of the important features to me of any system is noise level but I can't find much info to compare.
I am setting up a new shop after being in the old one for nearly 23 years. I have shopped everyone in the marketplace and visited a Grizzly showroom. (a working showroom I might add) I would not be so bold to say that they are ahead of everyone with every product but their fit and finish is excellent for the price. I use a Grizzly dust collector and have been more than satisfied with it's performance. I am a one man shop and it suits my needs as do the other five tools I have purchased from them.
I appreciate the response. Like yourself I work in a small shop and have been hear for 23 years. I have always sweep up all the saw dust with a broom. I have a bag set up to collect the chips from the planer. I just added a Williams & hussey molder and realize that my broom doesn't move that fast. My shop is in the country a bit but I do have neighbors. I try to keep the noise down when I can. Adding the molder wont help at all and adding a dust collector will only make it worse.
I appreciate your recommendation and will probably go for the Grizzly. I hope it is not as loud as my shopvac.
Tom
I will add this. If you live in a high humidity area then static electric buildup is not much to worry about.
I got the cheap 4" thin wall PVC at Home Depot that's used for drainage. Works great. I don't even glue or wrap the joints as they fit together with virtually no leakage. My rolling workbench is plumbed inside with it. The workbench hooks through the wall with a flex hose and blast gate to the DC that sets outside.
PlaneWood by Mike_in_KatyPlaneWood
How about that corragated pipe they use for draining house foundations (drainage tile). If you ground it, wouldn't it work ok?
Frank
Your main problem is going to be friction inside the pipe because of all the ridges. As steve said maintaining air flow and speed is the trick.
Frank - Go to HD and check out their 4" white thin wall pvc. An 8' stick is about $6, if I remember right. It's used for drainage and is smooth on the inside. The "L's" make wide smooth turns. It joins well to 4" blast gates also.
PlaneWood by Mike_in_Katy
PlaneWood
This forum post is now archived. Commenting has been disabled