I guess that my original question was, how good are CNC motion controllers when it comes to interpolating circles? Perhaps some are better than others. I am considering purchase of the KFLOP controller by Dynomotion. The CNC mill itself can cause problems if it is not sufficiently rigid, if the ways are not tight, or if the lead screws have backlash. But the advice that I am seeking has to do with the electronic motion controller.
I recognize that a motion controller does not alternate between X and Y motions but rather coordinates them to occur simultaneously. Still, I am imagining that there will be a series of "facets" on the largest radius arc, and these will only go away with manual finishing.
The reel back plate is a better item for discussion than the front end ring. The back plate has many surfaces that I can turn, and I usually finish with 320 and 600 grit, wet. But the OD with its 5 projecting lugs has to be milled. I first rough out this shape, leaving about 0.010 inch for the final passes. The really fiddly part is making all the final arcs meet correctly. There are 28 arcs in all, 9 are concave and the rest convex. (All concave arcs have radius 0.156 and are cut with a 5/16 end mill.) There are 18 points of inflection, where a concave arc meets a convex arc, and the part does not look right if these transitions are not tangent and smooth. This is where CNC should be a great time saver.
After turning all surfaces that can be turned, and milling the outer profile with light cuts, I tumble in stainless "jewelers mix". This tumbling removes all the sharp edges where the mill has cut the outer profile. It does not greatly change the appearance of the turned surfaces and the milled outer profile. I rely on manual mill and rotary table rigidity to make a good outer profile surface.
Dave
