It took a couple months of accumulating materials, a lot of drilling, tapping, and swearing, but it's done. This was built without a single weld. Everything is bolted together. I didn't follow anyone's plans. Instead, I boiled down the designs I saw others make into the simplest design I could manage that would get the job done. Then I realized it wouldn't *quite* get the job done, so I swore some more and fixed it.
This is the second motor I've used for it. The first was a treadmill motor, and the grinder worked great for about thirty minutes, and then the motor crapped out. Now it's got a single phase 1.5HP motor that once powered a mill.
The tracking mechanism is an old door hinge, and a knob with a threaded rod fit through a hole I drilled and tapped. Works pretty well.
The whole thing cost me around $500. Probably $100 of that was in mistakes, but it's still way cheaper than any grinder I could find for sale, including the slightly sub-par Grizzley knife grinder, which now is running upwards of $800.
All in all, if you've got the technical skill, it's a helluva lot cheaper to bang together your own grinder. And, this slightly sketchy looking contraption runs like a dream. Going from my old 1/3HP 4x36" grinder to this was like going from a Honda Civic to a Bugatti Veyron. Good stuff all around.