What is the best way (force/position/type of cinnamon) to grate cinnamon sticks using a microplane? I've tried several times, and although I get a finely ground, very aromatic powder, it took me five minutes to get a quarter of a teaspoon--and took serious elbow grease/constant repositioning. Is there any way to grate cinnamon more efficiently? Is it dependent on the type of cinnamon stick?
I think using a microplane to grate hard spice is only useful for small amount, either it will take you a long time (as you experienced) or will damage your microplane (render it blunt).
The best way to grind spices is with a electric grinder (coffee grinder), even with that, grinding harder spices like cinnamon is difficult.
Use a mortar and pestle to grind your cinnamon
As others have mentioned, you are probably using the wrong tool for the job. If you still want to do things by hand, you can use the "grater" side of a box grater for cinnamon and other hard spices like nutmeg (the side with outward facing "burrs"). You can also buy purpose made nutmeg graters.