I used a commercial coffee grinder like you see in the grocery stores for a couple years as my primary grain grinder. We have a local coffee company in my town that we do work for and they gave it to me, so you couldn't beat the price. Doing 25+ gallon batches, it really sped things up. Before I used it the first time, I ground a couple pounds of cheap base grain to clean out the residual coffee. Did this a couple times. (I guess you could always make a coffee porter/stout for you first batch and forgo the cleaning!
) You will most likely have to adjust the grind out farther than the coarsest setting. The problem with using this type of grinder is the mill itself is much more aggressive than a traditional corona type mill (what I use now.) It has teeth on it - not just ridges like a grain mill. It is certainly more a "grind" and less of a "crush". You will get more uncrushed grains, flour and smaller husks and a lower efficiency - BUT it will work. Don't forget the rice hulls! When using the coffee mill, my efficiency was always around 65%. I saw a large jump in efficiency when I started using the corona (as well as changing some other things in the brew process.) Now my efficiency is typically 85%+.
I wouldn't say I would recommend going out and buying a commercial coffee grinder with the intent of using it as a grain grinder, cause if you are gonna spend that much, you might as well buy a mill that is designed for grain. I now use it only for its originally intended purpose exclusively again!
BUT - if you have access to a free/cheap one - it will definitely work. It did for me for years.
Pros:
Very fast and easy to use and clean
Hopper held 15 +/- Lbs of grain
Very Durable - commercial quality
Got it for free
Cons:
Grinds more than crushes
Lower efficiency
Possible "stickier" mashes