Dust collection flex tubing, what's good?

How many places per foot do you have to anchor the ground wire to the PVC to dissipate the charge?

Hint. This is a trick question.

Reply to
George
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an infinite number.......

Reply to
bridger

Precisely. Which, I suppose, is tantamount to saying the wire is ineffective.

My 4" hose has a wire helix >

Reply to
George

Reply to
bridger

Yup.

Reply to
Bob Brogan

Ummm...yes, you can ground an insulator. Many people working in dry climates have been zap'ed from the generated static, and they've used wire or other methods to ground it out. Try using a comb or glass rod to generate static, then discharge one end.. You'll find there's little if any static charge left on the rest of it. Static charges do not propagate with the same mechanism as an electric current in a conductor. For static buildup on pvc you can:

1- Move it out of reach. 2- Wrap a wire (very small; current is low) around and ground it. 3- Spray lightly with c>>
Reply to
GerryG

Yeah. I'm expecting a Delta 1.5hp DC for my birthday next month, and so I'm doing a lot of reading on how to "duct-up" the shop. Almost all of the articles seem to be in agreement on the following principles:

o 4" is good. 5" is gooder. 6" is gooderer. o Try to avoid any hose/tubing that's not smooth inside. o Try to avoid tight turns (ie, use 45-degree bends instead of

90-degree). o For the same reason to avoid tight turns, avoid right-angle "T" joints and opt for the "fork-in-the-road" style "Y"s.

I'm taking so much of this as religion that my current dillema is this. I'm also planning on building the home-made cyclone in ShopNotes, but its outlet is at the top and the DC that it feeds into is going to have its inlet either waist-high or at the floor. So, I'm debating either raising the DC onto a platform or modifying the cyclone design so that I can get a more-or-less straight shot across from the cyclone exhaust to the DC intake.

- Joe

Reply to
Joe Emenaker

This comment is not to you so much as to a number of people here who say that bigger is better with ducts. I can see that as a general proposition, but at some point, relative to the size of the fan, won't velocity suffer in a significant way? And, doesn't velocity have a role to play in an effective DC system? After all, we are not just talking about air -- also talking about moving solid waste. Or, as is sometimes the case, am I missing something here? -- Igor

Reply to
igor

You are correct. When velocity drops too low, you cannot maintain the material in suspension - it just builds up in the pipes instead of flowing to the DC/pre-collector.

Greg G.

Reply to
Greg G.

Maybe. It really depends upon distance and the size of your dust collector. 6" may be *too* good and reduce velocity to the point where chips settle out. You really need to do the velocity/static pressure computations to be sure. In my case, 6" was too large, 5" was the ideal size. Unfortunately, that meant I could not use cheap PVC from the Borg.

Yep

Again, yep

Check out the various web sites like

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has an Excel spreadsheet:
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that is invaluable in sizing your system. Pay attention as well to sizing the ductwork for each machine.

I just went through this late last year and have been very satisfied with the results. I wound up buying metal spiral pipe from a local fabricator along with Y's, T's and elbows. I can now see plumes of dust being sucked into the table saw through the insert and the shaper table chips are sucked into the system with few residuals left behind.

Reply to
Mark & Juanita

you're not missing something. the bigger the duct the bigger the collector you need to have sucking on it. if the duct is oversize/collector is undersize sawdust will settle out in the duct.

Reply to
bridger

I found it!

Fine Woodworking's "Tools & Shops" issue Winter 2001/2002.

On page 48, Rod Cole (a MIT professor who's office is next an MIT prof who happens to be an expert in the physics of lightning), wrote an article called "PVC Pipe Dangers Debunked". He makes reference to an even more exhaustive report on the web. I searched Google for "Rod Cole PVC" and found this:

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Joe

Reply to
Joe Emenaker

I wouldn't worry. After making the way clear (and, as noted, maintaining pressure) for dust and chips on the way to the cyclone, it's only air you'll want to move to the impeller. It's a fluid, not a solid.

Reply to
George

You are actually right on target. Most of the various schemes I've found for plumbing a single user home shop seem to optimize around a 1

1/2 to 2 HP collector and five inch pipe. Four inch pipe is too restrictive, six inch pipe slows the velocity too much. So I tend to get frustrated with all the woodworking suppliers that stock only four inch pipe, hose and fittings.

So until I can find a big enough crowbar for my wallet, I am still dragging around the forty feet of four inch flex that came with my Penn State collector.

Reply to
Larry Kraus

I was thinking the same thing myself. In one of the downloadable reviews of dust collectors that are available at WoodStore, they mention that you need a certain number of feet-per-second of air movement in order to keep the sawdust suspended. They use that as justification for why you need "xyz" amount of cubic feet per minute from your DC.

The first question that ran through my mind was "Why don't you just decrease the diameter of your hose?". If you just went from 4" to 3", the velocity of the air inside the hose (provided that your CFM didn't suffer too much because of it) would go up by 60%!!!

Of course, there's also the other extreme. You don't want to hook up half-inch pipe as your ducting, either, because the CFM will suffer so much at that point that, even the small diameter probably won't help the linear velocity of the air (and you'd have the new problem of not drawing enough CFM from the *tool* itself ...).

Where the magic cross-over point is depends upon the CFM of your DC, how long and curvy your ducting is, and how resistant to airflow the inside surface of your ducting is.

- Joe

Reply to
Joe Emenaker

But you'd also get more clogs. 3" is getting down to the shop-vac hose territory.

Reply to
J. Clarke

Reply to
George

But if your running a one man shop, and running only one machine at a time, does it really matter if the main runs are 4" or 5"? I've got a delta 1.5 HP DC in my garage shop. I use 4" PVC sewer and drain pipe for the main runs and flex pipe to the machines. The delta has 2 4" mains coming off it so I ran 2 runs on each side of the shop. I don't have any problems with airflow even to the farthest machine, which is a planer. The PVC was cheap and easy to work. I also didn't bother to ground it although is does develop some static when I run the planer or jointer. But I look at it as a dust filter. The suspended dust in the shop sticks to the pipe. I just vacuum it once in a while.

Just my 2cents.

Reply to
Bill

Perhaps someone can point out the error of my thinking on this subject...

The system can only flow as much as the smallest port in the factory design. Take my Jet 1.5hp for example, what I'm getting at is that the port and hose from the blower housing to the bag hanging ring is, I believe, 5" diameter. To my thinking whatever size of the system outside of the factory setup is limited by this 5" - in other words, one can't fully draw 6" of main trunk air before the blower through a 5" hose after the blower - therefore the appropriate size of the main trunk should be no larger than 5" - or whatever the size of the smallest port in the manufactured assembly.

Wadya think?

Reply to
Fly-by-Night CC

Has to do with velocity. I'm sure others can explain it better. Let's say your blow has a true capacity of 1000 cfm. It will take in and blow out

1000 cubic feet every minute. If there is no duct at the entrance it will suck air from any place in the room it can. As you get closer to the blower you will feel the air moving. The more you restrict the opening, you will feel the air moving faster. The blower sucks in the air and puts it into a smaller outlet space and thus adds more force to the air and it moves faster on the way out. Ducting allows you to concentrate and "aim" the point of suction.

The blower can move 1000 cfm, but your compressor can make only 4 or 6 cfm, but when you glow that amount of air through a small nozzle, it feels like a lot more pressure than the outside of a fan or blower moving much more air. If the blower did not have enough velocity, the dust would just fall on the other side and not get moved into the bag. A window fan of the same capacity with not ducting will move little dust by comparison because it h as the cfm capacity, but at a much lower velocity. Ed

Reply to
Edwin Pawlowski

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