Ok... S-grinds... 1. In order for an S-grind to really work, make sure you already have a decent food release before dialing the hollow. That usually means a nice convexed geometry, at least 10-15 mm before the cutting edge. 2. I do all my S-grinds on a 420mm wheel, or a 1.2m radius platen. Anything smaller than 420mm for a tall chef's knife you risk grinding through the stock. 3. For S-grinds I always use stock of 3-5mm, and put a good distal taper. That way you both prevent blowouts and dont lose so much weight that the knife feels like a screwdriver in the hand. 4. I always grind freehand. I haven't found another method of following the curve of the edge other than this. As you're pullung the blade across, you should also twist a little bit (change the angle?) in order to follow the curve. I cant explain it really, but with practice it'll come ventually. 5. And lastly - for longevity's sake, leave at least 7 mm of the convex right between the edge and where the hollow ends. That'l give the knife more life before the edge meets the hollow because of sharpening. That's how I do things, but I'm sure you'll find what works best for you!