Knife Sharpener/Belt Sander

I didn't have any M3 hardware, but I did have a bunch of 6-32 screws and nuts, so I remixed this to use those. I have a glut of 18v Ridgid batteries so decided to power an RS 775 motor from an old Ryobi drill with a Ridgid 18v battery, using the trigger mechanism from a Ridgid X4 hammer drill I had lying around.

The thumb screw to adjust the speed is this design:
https://www.thingiverse.com/thing:1460364

I am needing to design a platen which uses a something more durable than filament, like a ceramic tile or chunk of marble/granite.