I have a Porkert mill, which is very similar to a Corona. There isn't much you can do to adjust them (hence the strong preference by most for the roller mills mentioned above). It has two rotatating plates that crush/grind the grains. The gap can be adjusted by a screw on the front, but the plates wobble a bit, so it is far from perfect. If you have a rotary tool, I have heard that you can grind down the spot where the plates connect to the adjustment knob to make it wobble less. Otherwise, it is just trial and error.
To attach it to a drill, just take off the screw that tightens on the handle, and remove the handle. Take that screw to your local hardware store and match it up with a bolt about 1.5" long with the same threads. Cut the head off the bolt with a hacksaw, and thread it into the mill. That's it.
I get about 70% - 75% efficiency with my mill, which is acceptable for AG brewing. I am still relatively new to AG brewing (6 AG brews), so I may come up a bit still. Others have reported 80% efficiency with their crush from a Porkert/Corona mill. But the big problem I see with this mill is that the crush can be inconsistent (some grains are pulverized to flour, some are left basically whole). I worry that this inconsistent crush might lead to inconsistent brews, which is a problem for AG brewing, particularly if you are doing recipe development and/or competition brewing. I think a Barley Crusher is my next brewing purchase.
invested in the Barley Crusher, standard hopper size. We power it with a 3/8" drill. Can crush 20 lbs. of grain in under 5 minutes, and the estimated efficiency of our brewery is pushing 80%.
