Building the two-bucket cycloneWhen I built the Thien-baffle style cyclone for my first small dust collector, making that cylinder out of wood was a lot of work. So for this one, I figured I'd just use another bucket as the enclosing cylinder.
I made a lid to fit on top of what was left of the bucket. This lid is a disk of plywood, with a ledge cut to fit just tightly inside the bucket. I cut the ledge by slowly turning the disk against a spinning table saw blade. The disk turns around a nail on the table saw sled to get an exact circle. I could have used a router for this too, but the saw was more convenient.
I managed to get the fit just right - it snaps in place with a satisfying pop. If you build one and can't get a good fit, you can always use caulking to seal the lid on.
To make sure the disk mounts level, I pre-drilled three mounting holes in the disk, then held the disk in the bucket and marked where the holes lined up. After that, I measured the exact distance down from the edge for each hole and drilled the mounting holes.
Some people prefer to just inject the air into a Thien-baffle with an elbow, but I prefer to not introduce any obstructions for the air circulating inside. So I prefer the shoot the air in tangentially through a hole in the side.
Getting the shape of that block right is tricky, so I designed it in CAD.
Drilling out the hole for the plastic tube that the hose will connect to. I used a drill press circle cutter to get the exact diameter I needed, then used a large forstner bit to hog out what was left in the middle.
The bucket is wider at the top than the bottom (slightly conical), so I tilted the bandsaw table by 1.8 degrees, so that the circular arc I cut along would actually produce a cone to match the bucket.
If you don't have a circle cutter and a large forstner bit, you can make the injector nozzle shorter and cut out a piece of plywood with a hole in it to attach to the face of the injector nozzle. I used that technique on my previous cyclone
A 2" ABS elbow fits into the lid. I'm using the style of elbow that fits straight into another elbow (as opposed to having a flange that fits onto a pipe). The main advantage of this elbow is that I can push it in so it rests flat against the lid.
The fit ended up very tight, but on the plus side, I didn't have to worry about fastening or sealing that elbow to the lid.
The first lid I cut up had just a rubber coating for the seal, so I found another lid, this one with a compressible hollow O-ring. The compressible O-ring seals much better if precision isn't perfect.
Ideally, I would glue the lid ring onto the cyclone bucket, but the semi-transparent buckets are made of polyethylene, and there's no such thing as a good polyethylene glue. I figured maybe I could melt the bucket and lid together in spots with a soldering iron. (Hint: don't do this)
I will rely on gravity and suction from the vacuum cleaner to push the cyclone onto the collection bucket, and if I have a small amount of leakage that's ok too.
A coping saw would be better, and I'm sure I have one somewhere, I just can't find it.
In a typical flat style Thien-baffle, the closed part of the baffle (where there is no slot around the perimeter) starts just after the injector, but with a much taller chamber on this one, the jet from the nozzle won't make it down to the baffle for quite a bit of distance, so it makes more sense to offset the closed part of the baffle.
I previously used felt as a sealer, but the problem with felt is that it often winds its way around a screw if you screw through it.
The hole on the ShopVac is just slightly smaller than the outside diameter of a 2" ABS pipe. But, looking at plumbing fittings in the hardware store, I found a threaded coupler, that, with the threads filed down, just barely fits inside the ShopVac's inlet.
Holding the pipe in a drill press vise allowed me to make a nice square cut on the bandsaw - much more precise than hacksawing it free-hand.
I didn't use any solvent cement to assemble the pieces. They make for a tight enough seal for vacuum cleaning as it is, and that way I can still make adjustments.
After my first bit of testing, I found the cyclone had gotten partially sucked into the collection bucket from the vacuum. I guess my plastic welding experiment wasn't a success. So I attached it with screws instead.
It was tempting to try the plastic welding technique again, but I figured if it failed at first for me it's likely to fail for others too, so I shouldn't encourage the technique.
Looking at the bucket, you could see the dust swirling inside of it, though in a photo it's hard to see, but there is a darker line from the top right to the bottom left. That's a stream of dust inside.
I weighed the bucket at 1043 grams empty, 1830 grams with the sawdust. So I had 787 grams of dust in the bucket.
With a lamp behind the dust collector, you can really see dark splotches of dust going around the dust collector. Very satisfying to watch.
I sucked that dust through very quickly. Sucking too much dust through a cyclone at once fast will generally slow down the rotational speed of the air inside, making it less effective. So it's a good stress test.
After sucking the contents of the bucket, I put my original bucket under to act as the collection bucket and sucked everything through it a second time.
So after going through the cyclone twice, I lost less than 0.8% of the dust by mass.
Now, where did that dust go?
A very small amount of dust ended in the bottom of the ShopVac. I'm assuming the rest ended up embedded in the ShopVac's filter. I should have weighed that before and after.
Ryszard's dust collector