I am figuring out the design of the air flow—mostly to allow for control of the air flow, but will need to catch the chaff as well.
I based what I am doing on what I know of older Gothot sample roaster which have a similar (well, mine is similar to the Gothot's). But I don't have one to play with, so am reverse engineering based on my memory and images I have found on the internet.
This video is of the easy portion—where the air exits the roaster and enters / moves through a wind tunnel of sorts, separating the chaff from the airflow. you can see where the chaff is caught in the dead zone below the hole it enters through. Still a couple refinements to figure out, but it is working.
The Cheesecloth was there cause it is a normal fan and not a n impeller, and I wasn't sure it would work (well, it didn't at first, which is why it is version 1.3 -)