I recently bought used Stanley planes #3, #5, #7. I think only the #5 had ever been properly sharpened, as I could see the factory grinding marks. I doubt the #7 has ever been used.
The #3 in particular had problems: pits and scratches in the base (which required light sanding off a burr), and the blade had pits in the bevel and on the back. The back also had a ding area about 1/2” x 1/4”, basically a shallow depression in the metal.
Learning to sharpen also instructs me on how to select used planes in the future!
The sharpening technique I learned (see notes on the class, earlier in the blog) started with 120, set on top of a piece of glass to which a 320 paper has been glued (only for holding the paper on top in place).
The teacher said sometimes you might go to 100 if the blade has problems. Well, I made only slow progress with the 100, so I tried 80, then 60. I did not want to use 60, because I know it makes deep scratches that you need to work up through the papers to get rid of. But even with 60, it took a long time to flatten the back.
As for the bevel, well, I figured it was a lost cause without a grinder. But I don’t have a lot of skill regrinding the bevel, so I have to learn by trial and error. The good news: I do have the Veritas grinding tool support and blade jig.
-- Mark, hack amateur woodworker, Medford (greater Boston) MA