In the past, I've tried using electric coffee grinders. I've ended up burning up 2 of them due to 1 common reason. The plastic washer underneath of the blade wears out quickly due to overheating and over-usage. It is possible to provide some sort of temporary fix for those, but once they are done.... they are done more or less. I won't explain. As a result, I've tried to go on a new limb. Hand crank grinders. This is slower, but consistent.
I've purchased a vintage old food grinder with 3 different heads for coarse to fine grinds. Today I spent a considerable amount of time hacking up a number of chaga chunks into acorn sized chunks to be fed into the grinder. I started grinding the chunks with the coarse head, and then processed the chaga again with the fine to get a good fine grade.
It is not an espresso grind, but that's why I got an extra espresso hand crank grinder from ebay.
Although this is hardly efficient yet, the vintage hand crank grinder is a life saver compared to the other methods used (electric coffee grinder and mortar and pestle). One more step to the hand crank vintage expresso grinder and I'll have the depth of grind best suited for efficient chaga brewing.
To your health and happiness.