Jim and Jim,
I'm not into Neanderhood enough to want a pit saw....that would be carrying things a bit far for me. If I ever want to get a tree trunk cut up into lumber, I will have a commercial sawmill do that.....I won't be buying a pit saw! Not to say that I want to discourage another Neander from doing such if his heart is really into it.....only saying it just isn't for me.
Concerning how to drive the wheel, my grandfather had such a grindstone out in his side yard, I think perhaps from when he was farming back in the 20s or 30s.
It was driven by two up and down pedals. The set up was you sat on a seat, kind of like an old style bicycle seat only steel, and the wheel was in front of you on a metal framework that was tied to the seat and the drive petals. The petals were on something like angle iron sections that extended forward one straddling each side of the frame. The back end of the angle iron pieces were on ground level attached to the frame, and they were on pivots at that end. These pivots were pretty much directly below, and maybe slightly behind the seat. The angle irons extended forward and slightly upward, and on the front end of them were petals that your feet rested on. When one petal was up the other petal rested on the ground.
The front edge of the petals had rods attached that pivoted on the front end location of the petals (perhaps attached to the sides of the petals at the front end of each), and the rods went from the pivots on the front of the petals about straight up to the ends of the grinding wheel drive device, which was shaped like the central petal drive assembly that the petals set on on a bicycle. On a bicycle this central drive assembly devise is what the forward chain drive sprocket is attached to. The center of this assembly went through the center of the grindstone and drove it. The rods attached to the drive assembly were about straight up from front end of the petals to what would be the equivalent of where the petals set on a bicycle drive assembly, and they pivoted on this spot where the petals would be on a bicycle drive assembly.
Thus the up and down movement of your feet was converted by the drive assembly on the wheel to a circular movement to the wheel.
This center assembly on the grindstone was virtually the same shape as the center petal assembly on a bicycle. When your right foot went down on the petals on the ends of the angle irons, the equivalent part on the center assembly on the grindstone went forward then down in a circular motion. At the same time the petal under your right foot was going down, the petal under your left foot was going up. Once you got the wheel started, its momentum carried the circular movement, and each press of the petals under your feet would drive the wheel faster and faster. We small grandchildren just loved to petal the thing. The wheel was pretty good sized, my guess looking back almost 60 years or so is that it might have been 20" to 2' in diameter. It was definitely bigger than some of the smaller ones that I have seen that are maybe 12" to 15" in diameter. My guess is that it might have been 2" wide or so.
Stew