[OklaWelder]

I'm trying figure out how to design a 4'x8' downdraft table. I have a 3900 CFM / 2" S.P. blower that I will use. I want to be able to cut small pieces without needing to cover the unused area of the table to capture the smoke. I know large tables are zoned, but a lot of companies offer smaller tables that are not zoned and they claim there is no need to cover unused areas of the table.

Obviously, I can just have one suction hole at the end of the table. I need a design that distributes the suction across the entire cutting area. I'm open to any and all ideas. Pictures would be great!

[flyinwilly]

I built a small table (2 x 4) with a water table and a downdraft system. I use a 960 CFM blower. I put a #60 mesh screened opening under the water table to catch the larger bits of debris/dust that are not caught by the water table. That opening is 2 x 1.5 feet. I am going to enlarge it the next time I take the water table out to repaint it, probably double the size. I have to clean the screens after every 30-40 minutes of cutting.

I've found that you get 3 types of debris when you plasma cut.
The first is the larger pieces that you cut out.
2nd. You get fine pieces of metal, almost like a dust.
3rd. Smoke - some from the oil on the sheet and probably even finer pieces of metal dust.

The water table does a great job of collecting the first 2 and the downdraft gets 99.9% of the 3rd. I don't cover any of the unused areas of the table when in use. However, when the table is about 50% uncovered, you can see the smoke curl out from under the sheet before it is sucked down.

Be sure to give yourself an easy way to clean out debris from under the table when you design it because you won't believe what plasma cutting will generate. I posted my build on the zone under " A Different Machine - Downdraft/water table". It might give you some ideas.

Willy