Some of you might have been following the saga of my new Harbor Freight DC. If not, here's part of the history, and here's the other part. Some of you also expressed interest in the collar that I added when I put in the neutral vane. I can save you some time...it doesn't help, and in fact it blows more chips into the filter with the collar than without.
Here's a video showing the amount of chips falling out of the filter after the DC is turned off, both with and without the collar. Even though the low-resolution video is a bit blurry, it's easy to see clumps of chips falling out of the filter when the collar is installed, and they're not falling when the collar is not there.
I don't know enough about the aerodynamics involved, but I suspect part of the problem may have been turbulence from all the tabs at the top of the collar. When I removed the filter to take off the collar, there was quite a bit of stuff stacked up that would have slid into the bag freely had it not been for all the tabs around the rim.
Regardless, the collar is now sitting in the scrap pile.