Mini dust collector part 2: the filter box

Having built the blower, it was time to build a filter box. I figured I'd use some 16"x25" furnace filters. I had an awful looking piece of plywood from a shipping crate that was just the right size, so I figured I might as well use that up. Here making the first cut. As often happens, the corner of the plywood it hit the column in the middle of my shop before I could slide it all the way across the saw, so I had to flip it to finish the cut.

The other sides of the box are made from some pine boards that came from discarded furniture. I rabbet joined them at the corners.

The problem with using this awful plywood is that it's not very flat. With my other dust collector I just relied on the wood getting pressed flat against the box for a seal, but that wasn't practical with this terrible plywood.

So I attached some cleats to the inside side of what will become the lid. But unlike when I built this crate, I thought ahead and mounted these cleats before closing the back of the box.

Here I'm screwing the cleat on from below. This allows me to get the cleats so they touch the sides of the box.

Then unscrewing it again, applying glue, and using the screws for alignment. I then put lots of clamps on to glue it on. After the glue dried, I took the screws out again.

Before attaching that side to the box, I cut the hole in for the blower and marked where it needs to go.

Then gluing it on the box. I used lots of clamps to force the warped plywood flat.

I needed a way to attach a hose to the box. This 4" to 3" ABS pipe adapter turned out to be just the right size. I cut off the 4" pipe part to make a flanged mount, which I screwed over a hole on the side of the box.

Then screwing the blower to the side of the box.

Inside the box, I added a small ledge to the sides to leave some space behind the filter. I also added some spacers near the blower to keep the pleats of the filter from getting pulled against the hole. Even though my blower is very low suction for a dust collector, it's still three times the suction of a furnace blower. At 5 cm of head, over the 16"x25" (40x62cm) area, that suction corresponds to 27 lbs or 12 kg of potential force if the filter was completely clogged.

Installing the filter. I sized the box for a tight fit - perhaps a bit too tight. I stacked two filters. These filters aren't designed for use in a dust collector, so I figured a second one would be a good idea.

Testing the box. With a yoghurt cup plugging in the inlet, there was still some airflow out the blower, so there is some leakage. Probably mostly around the lid.

Putting the box under my strip sander.

Ideally it would be oriented so the dust can fall away from the filter, but I don't have room for it in that orientation.

Then testing it with the belt sander by sanding away quite a bit of pine. This one is not as effective at sucking the dust in as my small dust collector is, but I didn't see a lot of dust getting airborne while using the sander either.

After sanding away quite a bit of material, I opened it up. There were some deposits of dust inside. With my other dust collector there wasn't any sawdust build-up.

Definitely not a powerful dust collector, but usable for small stuff like this sander or running it with a bandsaw. Though if I used it with a table saw, a slightly bigger blower would have been appropriate, plus a deeper box to hold more dust.

See also:

A different approach to dust collection