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
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.
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.
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
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.
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?
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
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. "
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
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.
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.
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
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
How do you propose gaining access to the duct to remove a clog?
Doug Miller (alphageek-at-milmac-dot-com)
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