Charlie, I'm planning to make an air cleaner and I saw your combination air
cleaner/sanding downdraft table/outfeed table in a Google search. Great
idea. I like the idea of the getting 3 functions from the same floor space.

A couple of questions:
I was wondering if placement in the room really makes a significant
difference in an air cleaner's performance. I've seen others suggest hanging
the air cleaner from the ceiling, by a wall, so it sets up an "circular"
airflow pattern around the room, to circulate more of the room's air.
A combination setup, being used as an outfeed table, too, most likely is
limited to being somewhere in the middle of the room, since that's where the
saw is going to be.
How does yours work in the middle of the room? Have you experimented with
different room placements and noticed a difference?

The truck air cleaners you mention on your web page - have you tried these
yet? Do you know how they're rated for efficiency or what size particles
they're able to filter out?
And since they're no longer usable on the truck, how much life do you think
they'd have left in them?

Thanks a lot. I already have a blower and plywood. The biggest question for
me left is what filters to use to filter the small stuff (~ 1 micron)
without spending a fortune.