I needed to replace worn-out and un-flat Diasharps. So I bought 250 grit and 400 grit 3"x8" Exe-Lap diamond stones because I heard they were flat. When they arrived, they were both convex, so I contacted Eze-Lap and they offered to replace them. Well I got the replacements and they aren't flat either. My expectation was that there would not be any slivers of light under a straight-edge on the surface of the stone (like when I hand-joint stock). This was not the case. When I put my Starrett straight-edge on the surface, I measure gaps of .003" on one stone and .004" on the other with feeler gauges. The stones are convex and these measurements are taken with the straight-edge in contact with the left portion of the stone and the feeler gauge applied at the right side.
I emailed Eze-Lap and told them this and ask them what their flatness tolerance is and whether these are in or out of spec. They never replied.
So I'd be interested in whether others have had better luck or the same experience and whether my expectation for flatness is unrealistic for such a product.
Thanks.