Quote Originally Posted by DIYSwede View Post
Thanks, Claudio.
AFAIK, the problems I had with my rectangular plates were that the upper, overhanging piece will get concave,
and the bottom one will become convex "real fast", then trying to straighten those new problems out
without a reference plate or a really sensitive comparator were more tedious work for diminishing returns.
I understand, that's why I said the length over width ratio should be really high, in a way that the overhanging weight wouldn't influence the contact with the underlying counter surface. It takes of course more time. I first used this trick to make flat my bars. To be fair my main target was straightness, but with a decent flatness. The scope was obviously different: I was not looking for to get a reference surface plate.
Eventually I had the chance to check my bars against a large, class 00, surface plate, and they resulted fairly flat with just a little spot on the corners.

Cld