Its all about air flow. Moving a lot of air moves a lot of sawdust. The stronger and faster the air flows, the more dust it will redirect into your DC system. Any restriction, particularly a sharp change in direction, will affect air flow so consider using Y connectors rather than a T. Too small a blower for the system is another factor that can limit air flow. Some people have cut holes in the table insert to increase air flow and help remove dust that gets trapped under the workpiece.
I think it was Mike who showed a picture of a shop made dust collection hood that was maybe a foot wide and about 2 inches high. It was nearly triangular with the dust collection near the back and sat just behind the bit, without a fence--I think it would be good when not using a fence, such as using a rail coping jig. Maybe he will repost it. If I were building that collector, I'd look at drilling a couple of positioning pin holes to quick set the hood in place.
I haven't seen much on the Keen setup, but collection as near the bit as possible looks like a good idea. I think you could easily set the Keen system up even in an enclosed box. I look forward to someone posting about their experience with the Keen. So far, no dust collector gets it all, so I'd probably still set up a box to capture what falls through. A front and door for setup would work and being wide open would help with cooling.
Last edited by DesertRatTom; 09-29-2015 at 11:43 AM.
Reason: addressing the poster's question