Well it ain't very pretty but does it ever work well!

[Rick T]

I made this 'top hat' design mostly from scraps lying around the workshop.
The top and bottom plates are 1/2" plywood, cyclone window is @1/8" acrylic ( strong and flexible). "in and out" ports are 5" dia-26 gauge galvanized HVAC pipe, dust slot is @ 1 1/8" wide and 240 degrees. Rather than using bolts to clamp the sandwich together I used 5" tall 'legs' with screws from the top and bottom plates. These legs butt up against the acrylic (which is set in dados) to give it more strength and rigidity. Initially I set the acrylic in a bed of latex calking in the dados but found the latex didn't adhere to the acrylic very well so I applied a liberal bead of 'Goop', an auto weather stripping sealant to the outer edge of the acrylic and it forms an air-tight seal. The upper lip of my old rubbermade garbage pail was pretty rough so I added an outer ring of plywood to the underside of the base plate that sits snugly against the outer dia lip of the pail and also a bead of rubber weather stripping to the mating surface of the underside of the lower base plate. This forms a near-airtight unit once the DC is running.
The total out-of-pocket cost to me was almost nothing and @ 3 hours time to build the unit and give it the fancy paint job.
It sucked up 10 gallons of mixed shop dust with no perceptible dust escaping the pre-separator.
I'm very happy with the performance so far and can highly recommend it. Thanks Phil and the others here who developed and enhanced the concept.

[Rick T]

I think 5" is my tipping point for moving sufficient volume and velocity using 10' of ribbed pipe.
I've been cutting some concrete floor in the shop with diamond saw and have been running the DC with open-ended pipe to capture the fine airborne dust. It has run for 6 hours straight and still has good suction so the separator must be intercepting the dust otherwise filter would have been plugged long ago. I'm almost afraid to look in the filter.

[Rick T]

I'm not sure if anyone has posted a pic of how the dust packs into the pail. There is a very distinct swirl pattern and the dust is hard-packed in the bottom so it is certainly under some pressure when it is forced down through the drop-slot. The center portion of the little mountain in the pic is @ 2" higher than the surrounding dust.  I've read some comments about the dust just falling once separated, but not so on my set-up anyway. I have a 'dust deputy' on my shop vac and it also hard-packs in the bottom of the collection pail but no swirl pattern.

[Rick T]

Chuck, if I'm understanding your observation correctly, and you are referring to the location and orientation of the inlet pipe.. very likely ours are the same. The picture I've shown above for some reason looks like an optical illusion.. maybe because it's taken through the acrylic window. The far side wall of the inlet pipe is tangent to the outside of the circular curve of the separator. The pipe is cut on a near-45 deg diagonal and extends  on the near-side to the inside of the arc of the interior of the separator.. about in line with the termination of the drop slot, and on the far side about 5" further. I made no attempt to fill the small voids around the inlet pipe but could have easily done so using spray foam insulation or something like that. I don't notice that material is particularly hanging up anywhere as it cycles around, but no matter, it's the results I'm after.
These things can be mesmerizing to watch in action...LOL