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Are you using CAM software to create CNC paths? I've found on similar parts that each depth leaves marks on the part as well as the rough finish you found. I now typically leave some 5 thousands material initially, then take a full depth finish pass to size. With a little cutting fluid, or coolant, that final surface usually comes out nicely finished. This is fairly easy with the CAM packages I've used. Though, it would be a little more involved with manual coding it's still possible.
Coming along nicely I am intrigued how does that commercial lap work? I could understand Ramon's with the little screw in the side providing the adjustment But I can't see how that one adjusts Jo