The Corona Mill is a cheap alternative to the more expensive roller mills used to crush grains for brewing. Roller mills start at $100 and quickly go up in price. A Corona Mill can be had for as little a $20. With three modifications---two minor, one a little more intense---it can be as effective or even more effective at crushing grains for home brewing. The lower cost will let you save money on other things like good brewing kettles, jet burners, and pumps.
Step 1: The Handle (Manual to Motorized)
This tip has been out there on the internet for a long time. The handle is held on by a thumb bolt. You can replace this thumb bolt with a 5/16" bolt and then use a 1/2" socket on a drill (or some other motor) to crank out your cracked grains.
Step 2: Another Minor Fix
This is another tip that's been out there a long time. See the exposed gap where the bolt is. Fill that with washers. Most tips around the internet say two. I say four because of the next mod.
Step 3: The Major Mod
I regret that I didn't think about making an instructable about this until after I'd finished it because it worked so well and it really wasn't that hard to do. The auger comes with a burr attached to it by a metal cap and a cotter pin. This makes for a very uneven burr. It's got a lot of wobble. I wanted to make it as even against the burr attached to the body as possible. The way I came up with is to cut threads on the post of the auger and use a nut and rubber o-ring to hold it on.
Luckily the post sticking out is 1/2". I used a 1/2"x13 die to cut the threads. It took a while. Not as long as you might expect though. I think all together I cut the threads in about 10 minutes.
The helped out quite a bit in leveling the burrs to each other. Because of the limited space I used a jam nut (they're thinner). If you could find a very thin lock nut (aka stop nut) then go for that. In this case the o-ring keeps pressure on the nut and keeps it in place. You could use glue or loctite to keep it in place if you wish. The o-ring also helped even out the unevenness. If you have access to a mill and lathe you could make one hell of a grinder out of a corona mill.
Step 4: Another Mod
Some people don't like the size of the hopper. You can use a 2 or 3 liter bottle to augment the size. I even heard of a guy using an empty 5 gallon water cooler bottle for this. I think he cut it down and screwed it to the existing hopper.
Get a corona mill. Well worth it for the money you save. And after these mods it'll produce a consistent grind that's easily adjusted based on the size of the grain. Having crushed 12lbs of grains I can assure you that you'll have very little powder from them (I had about 3/4c) and good sized hulls to keep you from getting stuck during sparging.