BuckyE wrote:
Do any millstones have concentric circles? The few I've seen had tangentially radial grooves, to lead the flour out to the sides. It seems to me a set of concentric ridges would not mill very well. But I'm not the expert, there.
You're right there, I think. But then again ... that could be why someone smashed it up. An aborted attempt at something different. A spiral would send stuff in- or outwards depending on how you turned it.