Before, I would just eyeball it on a bench grinder like this:
It got them sharp, but not at a consistent angle, didn't do it evenly over the whole blade and wore some excellent grooves into the aluminum support on the bench grinder. Doing it with an angle grinder probably would do a better job than this.
With the one I built, it's pretty easy. Just hold the blade flat against the support plate and go back and forth.
The grinding wheel runs in reverse [also did a reverse thread on the axle I made, so the grinding wheel wouldn't spin itself off], as it would probably wind up grabbing the steel and wedging it in the wheel and the support due to the sharp angle if it went CCW like a bench grinder. I'm using a 1HP 220V motor to run the wheel at about 3300 RPM.
I have a landscaping company and I sharpen a bunch of blades every week, this will make sharpening blades easier and more consistent then the old method I was using.
It's roughly modeled after the Magna-matic MAG-8000. I'll probably wind up buying their narrow grinding stone for doing mulching blades if I can't find a narrower one in a local store.
I'll get a side shot of the platform/grinding wheel and see if I can made some kind of short video showing how the various adjustments work.
You can see how the blade grinding process works from this video [using the Mag-9000, my setup works the same]:
