So, neotech, you would like relatively fast stock removal to a thickness that by eye looks right. Rather than trying to machine something to a precision tolerance and finish. That's what most people think of for a surface grinder.
And you'd like it to be driven by a stage with a magnetic base, rather than having to hold the knife blank with fingers against a belt sander, as you do now. So that sets the requirements.
But, maybe what you want is a thickness sander for metal rather than wood. If you do a search for "Thickness Sander" you'll get a fair number of hits for plans and photos of wood versions. That might give you some ideas.