In Part 1 of The Quest for an Affordable Dust-Collecting Cyclone, I got one of the facts backwards; luckily Stuart Deutsch (newly-minted PhD in Materials Science and Engineering, congrats Stu!) over at ToolGuyd wrote in to set the record straight. I'd incorrectly stated that "most of the dust (and particularly the fine particles) gets sucked away by the vortex," but in fact it's the reverse. As Deutsch points out,
Generally, cyclones are more efficient at separating out larger and heavier debris and particles. In terms of woodworking, they're better at trapping chips, shavings, and coarse particles, than lighter and finer dust that often continues on to the dust collector or shop vacuum anyways. Still, separators do greatly cut down on dust collector/shop vacuum maintenance.
Deutsch has also written a more extensive explanation of how dust cyclones work, and in our correspondence, kindly pointed the way towards two other DIY dust cyclone options:
The first, which is pictured at the top of this entry, is the Mini Cyclone Bucket Dust Collector, an Instructable written by a guy named Steli. Parts will run you about US $25 and it's "easy to build in a weekend." Steli lives in Europe, and when American readers commented that they couldn't find the common-in-Europe funnels in the size specified by Steli's design, he came up with an interesting suggestion:
"Buy an emergency street/traffic cone, and cut it down to your diameter size and length."
The second DIY option Deutsch put us on to is this sub-$20 solution, this one designed to be used under a blast cabinet, but still applicable to collecting dust from power tools. Interestingly enough, it incorporates a water trap in the bottom to capture the icky blast media, and features an interior baffle to prevent any splashing water from making its way into the shop vac.
The unnamed designer/fabricator of this particular variant offers some sage advice: "Don't fill the water above the pipe," s/he points out. "This is not a 'dust bong.'"
Given my earlier error of assuming a dust cyclone would prevent the smallest particles from reaching the shop vac, then finding out it was the reverse, I asked Deutsch if I'd still have to blow out the vac's filter and scrape the vanes—the very thing I'm trying to avoid.
"Periodically, yes," he responded. "Usually small amounts of fine and medium sized sawdust still make their way to the filter. Two options to reduce necessary maintenance is to swap the stock filter for a high efficiency disposable bag or an aftermarket 'Cleanstream' filter, [which is] HEPA-rated and much easier to clean than regular filters. I used water to rinse it clean, not compressed air, which made the task even less of a nuisance.
"Cleaning it is easy but not exactly effortless, but it's worth the investment over stock filters. Plus the higher efficiency gave me better peace of mind that fewer fine particles were being released back into the air of my small indoor workspace."
Whether I go DIY or Oneida, plus a Cleanstream filter, I'm now committed to incorporating a dust cyclone into my workstream. I'll keep you posted of how it goes.