He's done a great job so far.

I would seriously consider closing the loop with an encoder (or resolver) for each axis though. A robot arm is more likely to encounter obstructions, which of course would cause it to lose position. Going beyond steppers to servos, and one can see how something like this can start eating into your life savings. Might be difficult to rationalize to the missus that.

That's a very clever gripper design. Too bad he isn't (or can't) publish the STL files for that.