Max,
Take a look at this jig which really isn’t a jig at all. Fred Rowe invented the thing and many have found it to be invaluable, especially for just what you are doing. It allows you to do your grinding free hand yet right on the money, in effect “teaching” your hands how to do it correctly.
http://bubblejig.com/
http://knifedogs.com/showthread.php?10307-Flat-grinders-Bubble-Jig-with-something-to-grind-on.-July&highlight=bubble