I bought a small Lodge cast iron round griddle, not realizing that cast iron has changed from the smooth surface that my ancient cast iron pans have into a rather rough cooking surface. I was going to donate it, but I saw a video clip about re-surfacing and decided to give it a try. I put the metal grinding pad onto an angle grinder and started grinding. I was not happy with the wavy surface I saw, but it was too late, so I kept going. After the entire surface was bare iron, I switched to 40 grit and noticed some of the waves and gouges disappear. Then I switched to 60 grit and was even more pleased. Finally, I put some 80 grit sandpaper on my sander and lightly sanded the entire surface. It now has no scratches and is flat, not wavy. This process is very dirty, which black grit everywhere, even inside the protective goggles and dust mask I wore.
Next came the seasoning. I had no clue what I was doing, but I was simmering something low and slow in the oven, so I coated the surface with Crisco and put the bare pan in with the other food on another shelf. After several hours I took it out and found I had a sticky surface, but smooth. I was walking by Cookin', a vintage cookware shop in San Francisco, so I popped in to lament to Judith, the owner. She handed me an instruction sheet that said to clean the surface of the pan, put it into a very hot oven, and after half an hour take it out and rub it with Crisco while it was hot. So, I cleaned off the stickies and followed the instructions. Success! I had a smooth, non-sticky surface. Next, I'm going to work over a two-burner griddle.