Real Lalonde's Air Filter / Downdraft Table

I always wanted to build an air filter to hang in my workshop. I was looking for a furnace blower, but I was given this 2000 CFM commercial blower instead.

This unit is 27 inches tall and the squirrel cage alone is 12 inches wide. So it became soon evident that I couldn’t install this on the ceiling. I then decided to turn this project into a downdraft table/air filter/table saw extension instead. Because of the high CFM throughput, I was confident that this could work. The base is on casters and measure 40”X46”.

I mounted the blower right against the outside wall of the table in order to not create any wind turbulence. I caulked the seam between the blower and the wall.

The next step was to build an enclosure and cut holes for the filters. Because of the dimensions of the table, I decided to go with a dual entry.

The holes are made to accept standard 16”X20” filters, and feed directly into each side of the squirrel cage. Notice that all the enclosure seams are caulked to prevent unfiltered air from leaking inside without going through the filters.

On each side I use a regular furnace filter that protects a 3M Filtrete 1 micron filter. The filters are inserted a slot in the side of the table.

I then built an other slope beside the first one. This other side holds a shelf for the sanders and 2 drawers for my sanding supplies.

The table has two power outlets; one on each side, and the blower is controlled with a timer switch so I can leave it on when I leave at night. The downdraft tabletop is an array of 1” holes in a staggered pattern 3” on center ( 189 holes in all ! ). I then put a lip around the table so I could clamp my work if required.

The unit was built so I could use it as an extension table for my cabinet saw. It docks perfectly in the rear of the saw. It doesn’t come into the way of the Accusquare fence, and the miter gage clears the top of the table.

All this is nice, but does it work?

The fact that the blower is hidden deep inside the table makes it very quiet. I can leave it running all the time and it doesn’t bother me at all. The slopes provide a very good suction even in the corners of the table. I tried sanding a board in the 4 corners and the sawdust was sucked down right away. So it does its job as a downdraft table. It also does a very good job as an air filter. The fact that it picks up the dust from the top and expel the air along the floor, creates a circular flow in the workshop and clears the air quickly. In fact, after a couple days of using it as an air filter, the filters were already full of dust.

In summary, I’m very pleased with the result, and I hope this may help somebody in their designs of such a system.

Real