I've been using Cool Mist systems in my shop for many years. Good stuff, I like it, if it is mixed correctly. The drawbacks to Cool Mist is, it will stain your tooling if you don't clean up afterwards. I haven't had any problem with rust, except for rust on shavings. Again, you must clean up after usage. This is where a good shop vac can be of big help. Dad used to recycle the Cool Mist coolant as it collected in the trough of the machine tables. Don't do it! You can't get it clean enough to run back thru the unit without clogging the unit up. The last issue, is over time, the spray mist unit becomes clogged up from small bits of corrosion that form inside the unit. The corrosion that I see is probably more of a calcuim/line buildup than anything else. I do prefer spray mist over using flood coolant in my shop. What it amounts to, if you use your machines daily with a lot of machining, flood coolant is probably the way to go. If your machines stay idle for short periods time like mine do, go with spray mist. I only use spray mist on the mill. Very seldom do I use it on the lathe.
