dust collector duct work under concrete floor

hi:
I am planning to run the dust collector duct work for a future table saw under a concrete slab. Just dig a trench, place (sealed) duct work and fill over with sand? I suspect the sand fill is tantamount to a liquid over the long term so if the ductwork doesn't crush in say 24 inches of water, it won't crush in a few inches of sand under a slab. Is my thinking correct here? Or are there any gottchas? Ductwork is 6 inch diameter 30 gage.
Thanks
Jonathan
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>Jonathan wrote:

Is 30 gauge going to be able to handle the vacuum pressure? Tom Work at your leisure!
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As a retired sheetmetal worker I would suggest you use at least 24 ga. pipe and fittings. Also all joints and seams should be made water tight so moisture won't enter the system from under ther floor. If it were mine I would use glued PVC pipe and fittings under ground. Mike
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Jonathan, I would suggest using 4" ABS, glued for the underground part of the run. Moisture will get in otherwise. The 4" ABS will allow you to clean it periodically. I would not put other machines on the underground section. I would also run electrical conduit futures in as well.
Dave

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Under no circumstance should you use 4" piping for anythin relating to dust collection, until you make the machine connection, and that should be changed as well.
Also, 30 ga ductwork will work for a laundry exhause, and some light AC work, but under no circumstances should this be done for dust collection.
When you bury ductwork, you are alsays best off using an access panel for when it clogs or changes. 26 ga. for straight runs alone is the minimum. You use 30, and the collector will collapse it inside the sand.
ABS is a mass produced, fairly expensive form of ductwork that people like Jet sells for systems to pick up shavings, but not dust.
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Why not? I have installed it in a professional cabinet shop 10+ years ago. I was for a Unisaw and a 12" jointer. A blast gate separates the different machines. The system, both below the slab and above have been flawless.
You made a rash statement with no explanation, reason or offer even an opinion on the OP question. Why is that?
Dave

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It wasn't rash. 4" ABS is awful for dust collection. Note I did say that its fine for shavings. And simply saying you've used it in professional shops for years merely means that woodworkign professionals are not experts in dust collection. Few are.
You might want to check out Bill Pentz's now legendary website regarding dust collection.
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Again, comments without suggestions. Here is a quote from Bill Pentz's now legendary website :
"Strangely, when it comes to ducting, other than getting a professionally designed and built system using expensive smooth walled metal laser welded pipe, the low cost S&D PVC pipe (see my PVC site if you want to do "magic" with fitting PVC into your ducting.) is generally one of the best choices because it is smooth, far stronger than most HVAC metal pipe or spiral pipe, costs less, and fittings are a fraction of the price. Next best are the HVAC metal ducts. "
Dave

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snipped-for-privacy@aol.com (DarylRos) wrote:

I'm not sure what you might be an expert in, if anything, but it sure ain't posting in a newsgroup.
Don't you suppose that after touting a "legendary website regarding dust collection", you might want to provide a link to such a font of esoteric knowledge?
By the way, you don't mind if I adopt that for my own, do you? I'm a horrible name dropper and I'm just dying for the opportunity to throw out my intimate knowledge of "Bill Pentz's now legendary website regarding dust collection." That'll turn some heads.
--
-JR
Hung like Einstein and smart as a horse
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Thanks for the suggestions guys.
Jonathan

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Is this slab poured yet? If not, why not build a concrete form to form your trench, then use some sheet steel to cover the trench. If you incorporate a lip in your form, then the sheet steel can be laid flush to the floor and you don't have to worry about future access issues.
Joe

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I did this in my shop, but using 4 inch sched 40 PVC. I'd worry less about it than underfloor sheet metal in terms of collapse or corrosion. There could be condensation in the pipe under the right conditions.
Run PVC electrical conduit and maybe compressed air, too.
Also is wisest to run the pipe, then pour the slab, rather than the other way 'round. DAMHIKT

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This is one place that PVC pipe is the way to go. I would not put metal underground. Just be sure you ground the PVC to protect from the possibility of an explosion! (running, ducking!) ;-) Greg
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But if it is buried, isn't it automatically grounded?
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wrote in message

Not good enough, you need to wrap the pipe with wire and connect it to a grounding rod, that is, of course, driven into the ground! Greg
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How do you propose gaining access to the duct to remove a clog?
-- Regards, Doug Miller (alphageek-at-milmac-dot-com)
Get a copy of my NEW AND IMPROVED TrollFilter for NewsProxy/Nfilter by sending email to autoresponder at filterinfo-at-milmac-dot-com You must use your REAL email address to get a response.
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Doug worried:>How do you propose gaining access to the duct to remove a clog?

Work at your leisure!
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