Here is a sequence of photos that show you the process of grinding out the seat. I've prepared the seat by drawing the outline of where I want to grind to. Also i've drilled a few holes as depth gauges which I am able to use as visual guides as I grind away material.
This is the initial grinding operation, i'm grinding a groove around the outer edge of the seat outline. Pictured is an angle grinder with a Kutzall coarse carbide carving wheel.
Now I'm grinding out the rest of the seat I rough out the desired shape and grind down to the depth gauges i've drilled into the seat.
This is the Kutzall fine carving disc, I use it next to fine tune the grinding i've already done with the coarse disc.
Of course make sure your wearing your eye protection and dust mask while grinding and part of the chair. The seat grinding especially kicks up the saw dust.
Now I use a 7'' sanding disc to smooth out with grinding, I think it is a 60 or 80 grit disc.
Finally about an hour worth of grinding and we arrive at our seat with the rough shaping completed. Still I have many hours of sanding remaining just in the seat along let alone the rest of these custom bar stools.