Got an old printer? Make a rock tumbler

Nice build with an old printer parts.  Pretty simple too.  The only bits that I am concerned with is that a full fledged arduino was used (could he not use a simpler circuit?).  And …it takes 2 weeks to “polish” a rock.  That is a long time so no wonder he automated it.  A bit more reading up on it is you need to switch out the grit stone stuff you put into it after 7 days to get a nice shiny rock (start with SiC 80 milling powder if I understand it correctly).

http://www.instructables.com/id/Rock-Tumbler-1/?ALLSTEPS