Quote Originally Posted by Brian Holcombe View Post
In a time period where one can purchase a granite plate 18x24 flat to three one hundredths of a thousandth for a couple hundred dollars, I can’t see where a precision ground table can’t be made near perfectly flat. The difference is that one set of customers will definitely reject poor quality results and in the other case the customer most likely will simply let it slide.

The point at which to settle, in my opinion, is the point at which the level of surface flatness or similar metric no longer has a meaningful influence on the work. That number is closer to .001” than .010” in my experience.
i wonder if the manufacturers are sourcing their raw castings from a factory that does not allow enough time for the cast iron to settle? After grinding the metal can probably move too much resulting in a much less than flat surface.