it may also ruin your face and your whole life
do not proceed if your using a coffee grinder i thought this forum would not allow that sot of talk, i know a guy on youtube made some things himself used the coffee grinder for nearly a year[it could have happened first day] and it went up in his face he now wont touch anything flammable and i dont blame him. if you cant build/buy a mill get a pestle and mortar to start with you can make lift quality bp in 30mins but your limited to batch sizes of 10g depending on the mortar[you dont need loads to start with anyway right] use the coffee grinder to airfloat the chems seperately grind the c and s in the mortar for ten minutes with heavy pressure add the k and ten percent water i used to wet the pestle this keeps the dust down and speeds grinding grind for 20 mins and test, it should be dry from grinding, once granulated with 5%dextrin or corned with 2%this has lifted 1/2 inch to 3 inch shells
dan.
I didn't want to be blunt, but I'd agree a coffee grinder is a bad idea - I recall someone had charcoal ignite in a coffee grinder let alone BP. I would personally keep BP and finely divided fuels away from it.
I have used one in the past to mill charcoal to get some course mesh sizes for rocket tails, but it was a separate mill (attachment for wife's Bamix blender actually) it worked well, but she didn't really appreciate its new use very much.