Someone asked me for pics of this here while back.  Once the knife is adjusted, this does a pretty good job of duplicating knobs.  The 1″ dowels shown are for calibrating.  I wish I had something like it in cast iron.  I made the knife out of A2 and get about 20 knobs per sharpening.  Sharpening takes about 30 seconds using a 220 grit belt on my vertical sander.  Re-calibrating the knife takes about 3 or 4 minutes.