Baffle your dust!
Dust collection for CNC machines is always a hot topic and if you've ever cut a big project without it, you would probably agree! Dust collectors make a huge difference and help us keep our shops clean. But the down side to that is CNC machines produce an incredible amount to be collected and tend to quickly plug up the collector's filters. A recent trend in DC machines is the separator that pulls most of the chips out of the air stream before they get to the collector's impeller. They work great and dramatically reduce the load on the collector's filter. They also prevent big chunks from hitting and potentially damaging the impeller blades. That's the upside. The down side is that the manufacturers want to charge significantly higher premiums for their "cyclone" features. There is good news, you can build your own for well less than what they charge.
The simplest approach is a kit that you can buy for $20-50. Rockler has one for $30. Fairly simple to build with. They work though don't have the highest efficiency. And, if you have the skill to use the kit, you can take it to the next level with a top hat collector.
The secret ingredient in all this is the Thein Baffle. Invented by Phil Thein it works by pulling the air into a cyclone which slows the flow, allowing larger chips to fall. Because the flow follows the outer edge of the chamber, a slot in the baffle allows the dust to drop into a collection can below. The Thein Baffle (bottom plate) prevents the cyclone from scrubbing (sucking up) the chips that have collected in the bottom. The diagram below shows how it works. Some cyclone or vortex separators use a funnel design. While they look futuristic and cool, they take up a lot of vertical space. The funnel allows the dust to fall into the collection can and avoid being picked up (or scrubbed) by the cyclone. The Thein baffle prevent scrubbing and minimizes the vertical space requirement. The funnel is theoretically more efficient than the baffle approach. However, my testing appears to show that the top hat approach is very close to a funnel efficiency. See below for more on this.
Here is an exploded view of the top hat separator. I designed the top hat for my 4" dust collection system. The most complex part is the Thein Baffle - the bottom plate. There is a slot in the bottom that receives foam weather stripping to make for a vacuum seal. It was sized to fit the 30 gallon trash can I bought for it. The top has an 18" diameter. It scales fairly well but I don't know the smallest workable size can, probably in the 12" range. For the top and bottom, I used 1/2" Baltic birch. Other plywood can be used but I recommend BB. The curved side is 1/8" (actually 0.118") polycarbonate. The strip measures 48x4.25". I cold bent it even though the manufacturer recommends heat for this tight a bend. Acrylic could be used but might need some heat coaxing to bend without breaking. It fits into a 1/8" x 1/8" dado in the top and bottom. The other gray pieces are from scraps left over the the top and bottom. The bolts are 1/4-20 screw rod cut to 5 1/2" each and using nylon lock nuts. I did not need all the fasteners, 3 probably would have been good enough. Not shown are screws to hold the various small pieces of plywood together. The intake and exhaust ports are from Rockler.
Here's how it looks. Spray painted to match the Grizzly colors. The bungee cords will be replace with something a little nice but they work fairly well. The trash can gets sucked tight against the bottom of the baffle by the the vacuum of the dust collector.
Here is an overall view of my collection system. Forced to fit into a bay of my workshop, it makes some compromises, Foremost is one more 90 degree turn than I wanted.
The big question is "how well does it work?" I won't be making any quantitative studies of it but, based on a few hours of actual machine time, it looks really good. There is about 4" of dust in the trash can and just a light coating of dust in the dust collector's bag. Though, the photo doesn't show the bag very well. Some of the dust is in the filter itself so it is hard to make a definitive statement but I am very happy with the results thus far.
The dust collector is a Grizzly G0944 1 1/2 HP Wall Hanging unit. It has 1250 CFM spec'd airflow and filters to 1 micron particle size. I don't know what the minimum CFM is for my top hat design but would not want to have less than 800 or 900 for a 4" system. However, on another smaller Thein Baffle system I built, I get excellent results with a medium size shop vac.
Thein Top Hat shop drawings for 4" DC System. You will need to adapt these to your selection of collection can.
Because I am an engineer, there are always improvements to make. Here's my list:
Bevel the baffle slot (rather than round over) and do it on the bottom, not the top. It looks like the round over causes turbulence in the cyclone. Having a bevel pointing downward will push the turbulence into the container below.
Add a "bezel" for the trash can on the bottom of the Thein Baffle. This would make alignment easier.
Come up with a better collection can clamping system. Bungee cords work ok but just don't look professional.