Dust Collector Ducts

[lshuck]

I did not find a reference in the archives thru 2008 on this topic so, I am turning to you.

I am converting from a single purpose dust collector connection to the bot with no gates to an overhead distribution with 8 gates. I have been reading about the parts available but it seems to me that ABS 4" using standard plumbing parts up to the gates will do the job as there are wide sweeps etc.

I would appreciate any comments you may have on the this approach

[blackhawk]

Les - Yes, standard plumbing parts will work as long as your dust collector has sufficient cfm and static pressure to overcome the losses in the system created by the additional gates. It is always good to ground plastic pipes by some means.

The best duct work to use is the smooth metal type made specifically for dust collection systems. Of course, the huge drawback is its cost.

[tracys]

I use sheet metal fittings, but they are priced between the plastic and industrial type pipes. Here is a link to the info. http://www.kencraftcompany.com/Dustindex.htm

[ken_rychlik]

Metal piping here. You will have static electricity troubles with plastic.

Kenneth

[harryball]

I used metal duct from the box stores. Yeah, not the best idea but I've had no trouble with it. Everything is overhead and it will suck a cat through from the far end to the collection barrel. I'm using a 3HP Dust Gorilla from Oneida air. The cat was largely unharmed.

I visited a shop with PVC... the static was way too much. Dangerous if you ask me.

/RB

[gene]

I use heat and air snaplock metal pipe installed so the dust dont hang up on the crimped ends , sealed it and it works very good. I havent tried to suck a cat thru it tho:rolleyes: but the dust has no problems.

[curtiss]

Dust Collection Design Guide

http://www.woodweb.com/knowledge_base/Dust_Collection_Design_Guide.html


A dust collection design guide (in PDF format) originally written by Air Handling Systems - July 17, 2001

This document - "Designing Your Air Handling Dust System" - is a design guide originally written by Air Handling Systems, and has been converted into a two page PDF document (*requires Acrobat Reader*). Click here to view or download this file (http://www.woodweb.com/knowledge_base/_dust_collection_design_guide.pdf).

[Gary Campbell]

The article is good, Sandor's book is additional info. I have read and used both. Highly recommended

[gerryv]

Thanks guys, it's good and very timely info for an installation we're just about to start.

[michael_schwartz]

I am running about 2/3 galvanized sheet metal and 1/3 PVC.

Once you are used to working with it galvanized sheet metal is easier to install than PVC in my opinion.

PVC just is not designed for dust collection. It works ok, on smaller machines, and can be useful in some situations but I plan to avoid it the next time I setup a system.

[lshuck]

Thnx to all of you in helping to open my eyes and for the references. I do not have any cats around but maybe rabbits will be a good test.

Like most things, there is more to it than it seems when you are thinking about it. I am looking into the metal sys and compare costs to plastic but I can see the grounding issue is much easier with metal.

[blackhawk]

No cats for me either, but I did suck up a 16ft Stanley tape measure once that made it all the way through to the bag. The tape measure did not survive.

[bleeth]

Decent price on a Shop Fox at Grizzly right now:

http://www.grizzly.com/catalog/2010/Clearance/3

[navigator7]

I used metal duct from the box stores. Yeah, not the best idea but I've had no trouble with it. Everything is overhead and it will suck a cat through from the far end to the collection barrel. I'm using a 3HP Dust Gorilla from Oneida air. The cat was largely unharmed.

/RB

I know there is a market for that video! Where should I send the video and sound crew? ;-)

I went to an auction of a cabinet maker's biz rcently. He had 4" PVC ducting to a grizzly vac. The cabinet maker had been on location for at least 15 years ...and only one fire....solvent that missed the wood stove door opening.

When the winning bidder started taking things apart, he was frustrated by a copper wire inside. The cabinet maker must have known about static as there was an alligator clamp and an ohm meter by the on off switch. Evidently, they checked the continuity when the system was built and periodically since then.

Back to the sucking biological units.....I really see some possibilities here keeping the shop free of chipmunks, mice and whistle pigs.

[waynelocke]

I wish that I could remember where I read it but sometime back I read a woodworking article on pvc ductwork. The gist that I took away was that while theoretically possible, there aren't any verified small shop fires traced to pvc ducting and that that scenario is largely urban myth. I have heard the warnings as long as I have been a woodworker and do not personally know of any fires. Does anyone else?

That said, although I have used plastic ductwork, My current setup is all metal.

[myxpykalix]

their may be less of an issue with plastic and fires then reported but their is certainly more of a problem with static electricity and that will occur more frequently and screw up your work

[blackhawk]

Wayne - I read the same article years ago. I was able to find the link.

http://home.comcast.net/~rodec/woodworking/articles/DC_myths.html

[navigator7]

Wayne - I read the same article years ago. I was able to find the link.

http://home.comcast.net/~rodec/woodworking/articles/DC_myths.html

My searched revealed this link:
http://www.thewoodnerd.com/articles/dustExplosion.html

It appears the same principle that applies to gasoline also applies to dust. I never knew that.
We should en mass send emails to the Mythbusters. Those guys love big explosions. I'm partial to watching them too....on TV.

[harryball]

You cannot ground PVC. Correct. You can only discharge a collected charge from a dielectric material. The two are NOT the same. Grounding involves continuous flow of current preventing buildup of a stored charge. Discharging is siphoning off a charge to a grounding source. The amount you siphon off per unit of time is determined by how much charge is allowed to build. The more you siphon at one time, the stronger the discharge leading to a spark.

When you run a wire or strap to PVC all you have done is (hopefully)provide a least amount of resistance to discharge. If a discharge occurs soon enough there will be no spark. Thus making the pipe "safe". That is the theory.

I would not use PVC as a DC solution. The potential is too great for disaster.

Mythbusters did in fact setup a saw dust explosion on one of their shows. On a whim I also set one up in a bon fire on a smaller scale, 5 gallons poured into a box. I let the box start burning and the saw dust smoke... then I threw in a large rock and POW... impressive. I would NOT want that to go off in my shop.

http://www.youtube.com/watch?v=9o17mAJHdTo

While not a forceful explosion outside, imagine containing the fireball inside a shop while promoting the spread of the fire to the additional sawdust that did not burn. I have no doubt it would remove the shop doors and set everything on fire.


EDIT: someone will say "wait... siphoning off a charge IS grounding". Maybe in a pure definition but the effect is very different. In dielectric material, it has a high internal resistance and no matter how you slice it a charge is building then flowing. In a conductor the flow is continuous not allowing charge to increase then move, then increase again etc...


/RB

[dana_swift]

Suggested reading, the article I found in 2008 and posted about:

http://www.talkshopbot.com/forum/showpost.php?p=92954&postcount=23

Here is the link directly-
http://home.comcast.net/~rodec/woodw.../DC_myths.html (http://home.comcast.net/%7Erodec/woodworking/articles/DC_myths.html)

The link is still good, I checked it.
D

[Gary Campbell]

Guys...
In an attempt to be back on point of this thread.....

I am one who has used both PVC and metal DC ducting. In both high and low humidity, with both low and medium velocity systems. I have never made any effort to ground any of the rigid DC PVC piping. Those that have been to my shop know I have installed hundreds of feet of it.

For Les I have the following info:

I am not sure about ABS, especially in standard sch 40 or DWV sizes , but have no problem recommending PVC sch 20 (or 30) ie. drainfield pipe. There are many commercial adapters made just for this purpose.

All that mention it are correct. You can't ground an insulator. For dust collection purposes, you dont have to. Many sources state that there are NO documented cases of home shop sized systems exploding. PVC works fine for dust. The only disadvantage I have seen is that larger (6-8") diameters are not available, at least not to me.

Bowing to the knowledge of those more learned than myself, I concur that there is no danger in plastic DC lines, even tho they do generate static. Metal either doesnt, or allows it to discharge continiously so that no spark occurs. In either case, we small shop owners dont generate the quantity, volume or concentration of dust required to create combustion. And the jury is still out on whether static is in fact, the ignition source.

What is not acceptable is an ungrounded plastic dust hose to a CNC machine, especially a ShopBot, as there are many cases of this causing problems. The static charge that builds up in the dustfoot and flex pipe will discharge to the machine if not given a low resistance path to ground. Even tho I am guilty of using the generic term of "grounding", I mean "provide a low resistance path to ground".

Since owning a ShopBot, I have always done this for the flexible hose that connects the DC system to the ShopBot.

Hope this helps

[coach]

My DC for the bot is about 15' of the clear DC hose with the wire coil in it. That goes straight up to 40' of the 4" pvc pipe that Gary mentions.
I have never had a static issue. (he says as knocking on wood) I have used this set up for 3+ years.