My shop air cleaner has been getting a lot of use since I finished it. I make a point of turning it on and leaving it running whenever I’m working in the shop, which was unexpected – I fully expected that I would rarely remember to turn it on. The only downside with the design is that it can’t keep up with the dust produced from an extra heavy cutting (or sanding) session. It works great if left running for generally keeping the shop air clean while doing minor tasks, though.
So, to help with those heavier cleaning jobs, I figured I’d build a new air cleaner that can rapidly recycle the air in the shop for more efficient (but much noisier) filtration. The idea is that this cleaner will only come on when a tool is in use and shut off shortly afterwards. It will work in concert with the smaller one, leaving the smaller one running all of the time.
This article covers the design and building of the key component for the new cleaner, the fan.

The first thing I did was to mount a small aluminum pulley on the shaft of the motor to turn it truly flat using a 1/4″ chisel. I want to use this pulley as a durable hub for the fan and the casting is pretty rough:

Here’s a very short video showing how that was done:

The key is to go slow and do it in steps across the face. I had the motor clamped to the work bench and used a block of MDF in my quick release vise as a tool rest.

For the backing plate, I used a piece of 1/2″ Baltic birch plywood and used my beam compass to draw the 8″ circle. I then cut it out on the band saw and laid out lines in 30 degree steps around the circle with my shop protractor:

I figured I might as well make the blades on this fan backward inclined at a 15 degree angle. This is supposed to be more efficient, but I’m not sure if there’s a huge difference:

I set up a simple jig on my router table to hold the plate to cut the slots using a 1/4″ bit.

I transferred the lines I drew on the front to the edge to line up each cut and clamped on a stop block to limit how far into the plate it would cut:

The plate is 8″ diameter and I needed to decide how long the blades should be. I measured the current draw of the motor with no load, and found it to be a little over 4 amps. The full load amps for this one, as listed on the label, is 5.3 amps, so ideally my fan would need to run free-air (no housing) and not exceed this number:

I considered using just a single blade “propeller” mounted on the shaft to test how big the blades would be, but figured that would take longer than just making blades and cutting them shorter if the fan overloaded the motor.

So, that’s what I did. I made the blades from clear, well seasoned spruce cut to length on my mini table saw sled. I then rounded over the edges on the router table:

A quick test fit then I filled the slots with polyurethane construction adhesive to glue the fins in. The adhesive has a much longer working time than regular wood glue, which is good when you need to get this many parts in and lined up before it sets:

I made an outside ring from 1/4″ plywood and glued that onto the ends of the blades. I used pin nails to line up the blades and put clamps on every second one until it dried:

While the glue was drying on the fins, I glued in the pulley – hub with construction adhesive, then added washers and screws to clamp that in place:

The next day, the glue was completely cured and I could try to get it balanced. As you can see, that was difficult to do – I ended up drilling a lot of holes in one side and still didn’t get it perfectly balanced. Not really sure why that was, since the wheel was well put together, square and straight. The only thing I could see was that the plywood density was radically different from one side to the other.
Anyway, I mounted it on the motor and tried it out, but it was still too unbalanced to rely upon:

As it turned out, the fan didn’t come close to overloading the motor. I tested the current draw again while it was running and it was still just over 4 amps.

Another problem with that fan design was that it was more difficult to make, so I decided to try something less complex and use a material that has a very consistent density throughout – MDF:

Again, I marked the centre, then drew the circumference with my beam compass.

To cut the slots, this time I used my table saw and set up an angled guide (45 degrees) with a stop (the screw). This would take care of the diagonal cuts:

Then i could just use the fence to make the square cuts:

Cut in a rough circle on the band saw and I attached a steel pulley as a hub for this one:

To make the circle more perfect, I sanded it using a guide on my disk sander:

The fins for this one are easy, just pieces of 1/4″ plywood with the corners clipped off. After they were glued in, I could test it out:

This motor is faster, 3500 rpm. It’s also more powerful, drawing a little over 8 amps with no load. With this fan attached, it made no difference to the current draw, so it could have been bigger.

This fan was very easy to balance and ran perfectly. Because it is turning faster, it is a lot louder, but it does move a lot of air:

I wound up making a simple housing for it and I may use it as fine dust collection for my chop saw station to replace the low powered shop vac I’m using there:

The success of this impeller design encouraged my to make another, bigger one to run on the lower speed, lower power motor. I go into details on that in this video. There’s some unrelated (but still enjoyable) stuff at the first of the video, with the details on the fans about 4 minutes in: