Hi Amateur grinders,
found an easier and quicker method for beveling larger mirror blanks. Instead of taking what seems forever (hours), creating bevels on larger mirrors, (20"+ sizes), using knife sharpening stones, I decided to go hi-tech. Using a pair of belt sanders fitted with #120 silicon carbide belts was able to reduce time taken to a fraction that previously taken using the hand wielded sharpening stones.
Method: (Dry belt). Orientate grinder/sander at 45deg to top face/edge of the blank. I move the sander with approx 12" strokes clockwise, forward and back (not too quickly) a fixed number of strokes (I use 15 return strokes), then move approx 12" clockwise around the blank, and repeat the procedure until full circuit. Two (or three) circuits are completed, then you need to either rest the sander as it does get hot if run too long resulting in belt failure due to belt join glue melting or if you have a pair of sanders, then spell number one and do a couple of circuits with number two. About 5 (or 6) circuits of the blank will produce a neat 3mm to 4mm bevel.
Important Notes:
(a) As the work is by dry belt and glass dust can be injurious to health, lungs and eyes need to be protected, so nose mask and goggles are essential, also protection for ears (belt sanders are noisy).
(b) Very little pressure is needed with sander to glass as contact surface is very small, particularly at first.
(c) Best to do this work out doors. Dry conditions, preferably no wind.
Including a couple of pictures of equipment used and completed bevels (4mm) on my current 33" mirror project. (Over 207" of edge beveled).