The arbor for the sanding drums can also mount a grinding wheel. I got an 8″ 150-grit white wheel and used a dressing tool to ensure it spins true. I think I’ll get a second arbor so that I don’t have to re-true the wheel every time I swap it out for the sanding drums.
I was thinking of making a tool rest/jig for the wheel, but it has been suggested that learning to grind free-hand might be better in the long run. I found this to be true with sharpening regular chisels on bench stones – jigs made sharpening a time consuming process and it turned out that free-hand sharpening was not as frightening as I had imagined.
Update: A tool rest was later added to the grinder, as suggested by Shannon in the comments section. This turned out to be an important safety addition as well as making sharpening easier. See the post about making the rest here.