take a pair of wire cutters or tin snips and break the bark down to small bits , 1/2 inch by 1/4 inch  is a rough estimate. that will get it small enough for the coffee grinder.  def wear a mask as you grind, the pink dust floats everywhere. its good to do your grinding over a metal bowl or receptacle to catch stray dust, also sometimes the grinder will get a little clogged and spit dust out the sides while grinding.  dont let the machine overheat.     vortex's tek has good notes on this process :    http://www.dmt-nexus.me/phpBB2/viewtopic.php?t=70