NOTE: The Hario/Porlex compatible drill adapter shown below is available for sale! You can find it on Shapeways, here.
I got a Hario Skerton manual coffee grinder a few years back, but quickly grew tired of the hand cranking (+ the jumps & catches & spills I frequently had with it). So I retrofitted mine with a nut instead of a thumbscrew, and have happily been using a drill with a nutdriver to grind my coffee.
A friend has the Hario MSS-1B Mini Slim grinder, and he has it even worse: The shaft has a pentagon stud, which has a loose fit with the stamped handle and is difficult to adapt to a drill. We were talking about his situation this week, and I decided to model a pentagon driver that could be 3D printed and would allow the user to use a drill to grind their coffee easily & quickly.
I realize that this is a pretty small market - people who are okay with having a drill in their kitchen - but I'm curious whether anyone else out there would be interested in something like this. I'll be testing a prototype of the part over the next few weeks; if you're interested, give a holler!