Funnily enough, I discovered your project on the same day I got a free random motor. That looks like an excellent machine to use. I've only glanced through the thread at this point, but I like the design, and I feel like I can feel it through my computer screen. It feels crisp, solid, and accurate. You did a nice job on that!
What kind of torque does your 90 RPM motor develop? The data plate on mine is illegible, and I have no clue how fast it turns, but it's probably way too fast. I would have to gear it way down, which would increase the torque considerably. That seems acceptable for something like this. I have a commercial diamond knife grinder whose wheels bog down at the slightest touch, and it would be better with more torque.
I think I have a use in mind for this free motor. Now I just need to source some free metal that's nice and rigid. Well thanks for giving me something to think about, and congratulations on a really nice build!