- The closer you get to the source w/ your DC and vacuum, the better for your lungs and your shop. That pretty much means a downdraft table, as Bob and Alan suggested, AND [STRIKE]or[/STRIKE] a vacuum hose connected directly to the tool.
- Second best is squirrel cage or other types of fans just a very few inches away from where you are sanding, that draw the dust into good filters or vent to the outside. There are some nice setups where people have lined the back of a wall bench with fans that blow directly outside. Others have taken that idea even one step farther and built a hard shroud over and and along the sides of the bench top and added a curtain made from strips of clear vinyl across the front .
The problem with the next two options is that by the time the dust finds its way to the air cleaner, you who are closest to the source have had plenty of time and opportunity to inhale a significant amount of it, and a lot of it has drifted and settled elsewhere! There is little substitute for capturing it at the source.
- Third [STRIKE]Second[/STRIKE] best one of the overhead units, such as the Jet model pslamp32 suggested. They have excellent filters and do a good job of cleaning the air.
- Also third best is what I use. Old squirrel cage blowers mounted in boxes, w/ the air passing through one or more filters before it is exhausted. The quality of filters you purchase can make a big difference in the efficiency of these units. One advantage these units can have is they also serve as a fan blowing cool air across the shop when it's hot. See pic below for example.
When I was researching DC systems for my shop, I came across another idea. If you have permanent duct work in your shop, you can mount a shop vac filter to the end of a duct. It will pull air through it and clean it. The downside of this is that you have to leave the DC running all the time.
Remember, you need CFM to move the volume of air, but if you add any restriction like pipe you need some static pressure suction.
I made this unit primarily as a fan for hot days. The air filtration was kinda an afterthought. If I were to redo it, I would use two filters on each side.
HTH
Bill