This is how it used to look. The fan itself has only one speed, but I can adjust it to any speed with my 2.4-kilovolt variac transformer from the shop. Blowing up from the basement helps cool the house quietly, but the airflow isn't very good this way.

The cage started out as a 4'x5' piece of metal mesh for concrete work, which I had to chomp into a workable form.

Then using the plasma cutter, I made the final adjustments, which I MIG welded into the final shape.

The mesh itself is too coarse for a safety cage because the wires are about four inches apart. Luckily I had a huge pile of surplus wires to weld into the gaps. The only problem is that they're galvanized, which produces nasty fumes (welder's flu), so I had to wear a full respirator and actually run the fan while welding. Doing this outside wasn't an option at the time.

And here's the final product, after only a couple hours of work. The back side here is garden mesh with one-centimeter spacing.

The front is roughly one-inch spacing, but it's projected far enough from the blades that you have to try hard to injure yourself.