Originally Posted by
Ty Williams
I asked to exchange the Atoma out of curiosity and the new one arrived today. It's flatter, but still not flat. There's a MUCH smaller section of the face that's concave by right about 0.0015" (15 ten thousandths). I tried some googling. Lee Valley says the Atoma is guaranteed flat to +-0.04mm, which is 0.0016", so my plate is just barely in spec. DMT says the DiaSharp plates are flat to within 0.0010", so they're flatter than my 2nd Atoma. DMT also says their DiaFlat line is flat to within 0.0005" (5 ten thousandths) so about 3x flatter than my 2nd Atoma but also about 3x more expensive.
Those numbers are meaningless, of course, without knowing what precision is required for our uses. My gut feeling is that the edge of the tool needs to be flat/planar to within the size of the scratch pattern the abrasive is leaving to maximize the edge quality at that abrasive size. With the Shapton Pro 5k I finish on, that means 3 microns or about 1 ten-thousandth of an inch. What I have no idea about is how flat the start of the chain (the Atoma in this case) needs to be to ensure that the final product is as well sharpened as it can be.