QUESTION: Dust collection plumbing. PVC or metal duct?

I finally retired my shop vac, always had to wear ear muffs. Bought a Jet DC, the dc 650. Wow! So quite and it was interesting that when I hooked it up to my table saw, I hadn't cut any wood but it had much more power than the shop vac. I pulled the table insert, looked at the amount of dust inside, then turned on the DC and couldn't believe the dust that the shop vac wouldn't get disappear with the Jet. SO, I now need to hook up my vents. I've read on the net PVC vs. metal. It's like cars, everyone has thier own opinion. From what I've read, I'm leaning towards metal. Will go shopping and compare prices. I don't have that much to run in my basement shop. Opinions?
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Honestly, a 1 HP dust collector is underpowered to use on a central dust collection system, except for extremely short runs. The way to get the most efficient set up is to use a straight run along a wall, maybe 2-3' off the floor (i.e. don't go vertical up and down from the ceiling). The best use for this size is to actually wheel it from tool to tool, or use a length of maybe 10' of flexible 4" hose.
I went up to a 2 HP unit, and use it with 5" PVC main line and 4" drops with a total duct length of about 30' and it works o.k. I think the guys with the cyclone dust collectors have better overall performance.
Anyway, I'm sure there's a way to set yours up to get best use - just don't be surprised if you don't the same performance when you run it through a lot of PVC as you did when directly hooked up to your tools.
BTW, you can see what I think about the duct material - PVC works great. And, before you get inundated with warnings and scare-talk - it is a myth about dust explosions in small woodworking shops (there has been MUCH discussion about this, and even scientific testing - woodworking magazines have run articles on it, etc. etc. - and all of them say the risk of explosion is nearly infintesimal). You can ground the PVC if you want, but that really isn't necessary either. Just be sure to avoid sucking up metal bits (screws, nails, etc.) that might cause a spark if they hit the impeller of your DC - THAT can start a fire in your dust bags/container.
Mike

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On Fri, 19 Nov 2004 18:40:08 GMT, "Mike in Mystic"
......and in reply I say!:
remove ns from my header address to reply via email
I did some quick plugging in to a little programme I have that does air flows.
IIRC the 1HP units claim around 600CFM usually? I imagine that the figure is quoted with NO pipe on the unit. It is complicated by the need to push the air through the filters.
These may help. I am not sure of the _absolute_ meaning, as it its' a complex system. Other may elucidate.
But larger pipe is good.
I _think_ that needing to use 2/3 HP to shove 600CFM through 4" pipe means that power is _lost_ in the pipe, and will represent a dramatic drop in performance of the DC, due to the fan's being only partially efficient etc.
If you were using dead straight pipe, then     - 4" pipe up to 45ft long would need 2/3 HP.     - 6" pipe up to 45ft long would need about 1/10 HP.
So pipe diameter is dramatic on long runs.
I plugged in a couple of elbows:     4" pipe, power went from 2/3 HP to around 1.2HP, each elbow was about .15 HP     6" pipe, power went from 1/10 HP to around 1/6 HP, each elbow was about .03 HP
Again bigger pipe makes a huge difference.
Which is why this bit....

***************************************************** Dogs are better than people.
People are better than dogs for only one purpose. And then it's only half of ofthe people. And _then_ most of them are only ordinary anyway. And then they have a headache.........
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wrote:

interesting, nick.. and it makes sense..
I guess the elbow thing is sort of a "damned if you do, damned if you don't" kind of thing, especially when applied to a cyclone.. I wouldn't want to use my DC without it, but among other issues, you're adding at least 2 elbows to make it work..
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vaguely proposed a theory ......and in reply I say!:
remove ns from my header address to reply via email

Thank god for that! Doesn't happen often....<G>

I think it's why MinM was saying don't go across the ceiling. You add one more right angle to each unit, and probably turbulence at each T even when the air is going elsewhere. In fact I checked, and a Tee, flow _through_ (not around)_ the Tee, is about as bad as an elbow, going round the elbow. Going round from the cross to the leg of a Tee is a killer. Tees are a real no-no according to this set of calcs.
Sweeping turns help quite a bit. The prebuilt elbow is the killer.
I don't know about cyclones, except that they free up the DC and the bags so much that _sustained_ performance will be _hugely_ increased.
Inside the cyclone of course, the rules change. The air slows right down, as you are effectively running a 2' diameter pipe! <G>
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You should always wear muffs whilst using power tools. Just because a tool's acoustic output isn't 'obviously' offensive to the ear, doesn't mean it isn't doing damage. Use muffs because those plugs are not a good idea as they tend to ram waxy sawdust into the ear canal during insertion.
JM2CW
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vaguely proposed a theory ......and in reply I say!:
remove ns from my header address to reply via email

And your problem with _that_ is? <GG>
Seriously, it can be a problem. I use them a lot, because I need hearing protection just about all the time, and muffs are a PITA. But the wax problem is real.
Sorry...what did you say? <G>
***************************************************** Dogs are better than people.
People are better than dogs for only one purpose. And then it's only half of ofthe people. And _then_ most of them are only ordinary anyway. And then they have a headache.........
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wrote:

In this weather they keep your ears warm.
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I am currently installing ducting for a cyclone. I'm using 6" PVC, ASTM-D2729, also known as S&D. Much lighter than the Sched 40 stuff. According to Bill Pentz's web site <http://billpentz.com//woodworking/cyclone/index.cfm it's as good or almost as good as the Spiral Wrap steel ducting. My cost comparisons found that the locally purchased S&D PVC was about 1/4 the cost, overall, of the SW steel, not considering shipping costs.
You don't say whether you're considering the SW steel or HVAC ducting. My opinion is that you should read what Bill has to say about it before you write any checks. He also has some things to say about desirable modifications to commercially available DC units.
Tom Veatch Wichita, KS USA
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Metal's better, but the "exploding dust" reason is bogus.
Go with what you can afford and fit. Custom metalwork from a HVAC shop is cheaper than you think.
--
Smert' spamionam

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