Given that a shop vac can deliver much more suction than a dust
collector (albeit while moving less air) the added static pressure of a
trashcan separator should have minimial impact on the airflow.
Like a ton less air! A typical shop vac will move a tad over 100 CFM. A HF
dust collector is rated at 1200 CFM, but my bet is they are bragging a bit
high. Even so, about 10 times the air flow. You need air flow to move chips,
static pressure, (suction), don't do squat for moving chips. Moving dust you
have pretty much zero static pressure any way, maybe 4-5 inches of water
column. Skip the trash can separator and try the shop vac direct, it still
won't do a very good job. A few years back I tried doing this with two shop
vacs hooked up, and it still didn't work. My el-cheapo HF dust collector bet
it by a mile.
On Wed, 03 Oct 2007 16:32:49 -0600, Chris Friesen wrote:
Probably not. The key is how you define suction.
Most people think of suction as either air speed or how much pull the
end of the hose has against your hand. But these are only components
of what really defines how much dust is collected: VOLUME OF AIR
MOVED. According to, http://yarchive.net/metal/shop_vac.html , the best
a shop vacuum can do is 140 CFM, whereas most (real) dust collectors
START at 800 CFM and go all the way up to 6,000+ CFM.
Bill Pentz Dust Collection site is a good primer:
I'm defining suction as vacuum pressure, or water column inches, or
Of course the shopvac won't move as much air as a dust collector, it's a
totally different design. However, because of that difference in design
adding a separator to a shopvac will have minimal impact on the volume
of air moved because it can easily overcome the static pressure of the
Conversely, a dust collector moves a lot of air but is sensitive to
static pressure increases. Thus adding a cyclone or trashcan separator
can have a large impact on the airflow (depending on the fan curve, of
On Wed, 03 Oct 2007 22:28:28 -0600, Chris Friesen wrote:
You can suck the same water column through a plastic coffee stirrer as
you can a large straw. But you would never drink through the stirrer
because you can't pull drink through it fast enough to be useful.
Same thing with a dust collector. No matter the pressure at the
motor/impeller side, through a 2-1/2" hose you simply can't pull
enough air (entrained with dust). You need at least 4" duct, but
preferably 5-6" with a motor/fan sized accordingly. The magic number
is 800-1000 CFM. Imagine a 10'W x 10'D x 10'H room. Per minute.
So a shopvac moving 100cfm through a 4" hose gives much more suction than a
DC moving 800cfm.
What exactly is your definition of suction?!?!
A shopvac will do better when attached to a ROS than a DC will, but that is
only because the openings are so small that the DC is starved for air. A
planer is an example of where exactly the opposite is true; the DC is 5 or
10 times better.
And if you did put a separator on the shopvac you had better seal that
sucker perfectly, as any leak will pretty much kill it. A DC doesn't much
care about small leaks.
probably true, but not difficult to do as you can see from my one.
The cyclone is sitting on an expanded polystyrene disk on the paint can
lid that has another expanded polystyrene disk under it and is just
screwed together. FWIW sometimes I forget to seat the lid firmly but
then the suction keeps the lid on and no special care is needed to seal
it until I turn the shopvac of.
The reason for the lashup is that many materials are hard to come by in
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