So I decided to make my own. For the hardware I used two 3' sections of 3/4" aluminum tubing, a 12" lazy susan and a 6" HVAC flange.

I figured the hood was three different assemblies, the hood itself, the lazy susan bracket and the mounting bracket.

The hood size was based on what was listed for the downdrafter. Here's a picture as its being assemblied.

Its just a 5/8" bottom with 1/4" sides and back.

And the lazy susan bracket was pretty simple also, though I made it from 3/4" plywood.

With the 12" lazy susan I was able to get a 6" hole through the middle for the dust collection.

The sides have two holes drilled in them for the aluminum rails that the hood can slide back and forth on.

Then came the mounting bracket to attach the entire thing to the miter stand.

The lazy susan allows the dust hood to pivot and the aluminum tubing allows the hood to move from side to side so as the miter saw is pivoted for miter cuts the hood can be positioned so it collects the dust.

Then it was just a matter figuring out where the hood should be positioned on the lazy susan so I can cut a hole in the bottom for the dust collection.

Once that was figured it I mounted to the back of the miter saw stand.

Here's another angle.

I haven't listed any measurements because I pretty much just winged it based on the scrap plywood I had on hand. The only things I had to buy was the aluminum tubing, the lazy susan and the HVAC flange. Doing it again I think using either steel tubing or 1" aluminum tubing would be better since the weight of the hood causes the 3/4" tubing to flex a bit.

 

So how does it work? All the dust that goes into the hood gets sucked into the cyclone. But the saw doesn't shoot all the dust into the hood so I can't say I get 100% collection. Its probably close to 85% which is much better than nothing.