Old chisels with nicked or rounded tips will need to be reshaped. Use a belt sander or grinder to remove nicks and shape the chisel to a 25-degree angle. If you’re using a grinder, dip the chisel in water every two or three seconds to prevent the tip from overheating and turning blue. If this happens, the chisel won’t hold an edge for long.
Next, polish the back of the chisel by rubbing it back and forth over progressively finer wet/dry sandpaper, pressing the back perfectly flat to the paper. For all sharpening, a good progression of paper is 120, 220, 400 and 600 grit.
Finally, set the honing guide to hold the chisel at a 30-degree angle to create a “secondary bevel” and run through the grits, starting at 220. Lightly glue the wet/dry sandpaper with spray adhesive to a piece of 1/4-in. glass with smoothed edges. Roll the chisel back and forth over the sandpaper until a burr forms on the back of the blade. Turn the chisel over and stroke it flat on the sandpaper to remove the burr. Then move to a finer-grit paper and repeat the process.