I am building my own router table and have progressed to the point where I need to add the dust collection. I am trying to keep things slimmed down in the back so it will stay closer to a wall for when it isn't being used. This design (the one on the right in the screenshot) would only protrude out from the back about 3" instead of about 5" if I were to put 4" fittings on the back. And just having the 4" fittings exposed directly on the back, there is more likelihood of damaging one when moving the table to the wall. Since there is a 2" overhang for the table top, that would be only another inch or so from the wall. I am curious if a plenum system on the back, such as in the screen shot attached, would work. This is a really simple Sketchup drawing. The parts of the plenum that extend on the right and left sides of the table back would have a 4" port on the front side for attaching to my Jet DC-1100 dust collector. Each one of the 4" ports would have a blast gate to close off the side that is not in use. There would be two 2" holes in the back that would collect from the router compartment, and one on the top of the plenum for a hose to go up to the fence, also with a blast gate for when I am not using a fence.
Your thoughts??
Wayne
P.S. The area of a 4" circle is about 12.5 sq inches. the area of three 2" circles would be about 9.5 sq in, and the area of three 2.5" circles would be about 14.7 sq in. If the plenum had a rectangular cross section of 6 x 2.5 that would be 15 sq in.