This gets discussed a couple times a year on TFL. Some say it's dangerous, some say not (I say not, when simple/logical safety precautions are followed), but most all agree it is a waste of time given the availability of inexpensive subs and real BP - all of which will be much better than the best you can grind out at home. I say go for it if your reason is to "learn" how, but not if your goal is to find a practical alternative to manufactured BP and subs.