It being summer now, my local hackerspace Sprout has started needed ventilation. We have a box fan (and, over the years, I've had several) that had no knob. Did we lose it? Did it break? Did the knob fairies make off with it? Who knows. I do know that my fingers hurt from trying to turn it and I never seemed to have a pair of pliers handy. I did have a Thing-o-Matic, though...

I started by downloading Stove Knob by wizard23 and while it did technically work, the hole for the shaft was too large and my fan, like many others I have seen, gets along better with a knob that has a shaft receptacle extending a good bit beyond the back of the larger, human-friendly knob part. I started over and spent a few minutes in Sketchup making a model.

The first print didn't provide enough tolerance for the ooze and the shaft of the fan switch wouldn't fit. I scaled it up a bit and the third try worked perfectly.