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Thanks for sharing. Do you also cut a taper at the top of the piston?I would think a fairly good lathe(Hardinge HLV-H or Schaublin) is needed to make a useful piston like this, especially hand feeding. I have a PCD grooving tool that will take off such thin chips, 1mm wide chips float away. I don't think my old Clausing is in good enough condition to turn the OD of a ringless piston. The highschool students who beat on it previous to my ownership, crashed the chuck into the compound slide so many times it looks like a dog chewed the corner off.With .01mm/rev and .4mm nose radius theoretical surface roughness well into lapping territory. Real results are completely dependent on the material and cutting edge. The only thing sharper than these sharp edge PCD is monocrystalline diamond. You can cut cast iron with diamond, but CBN is typical. Cast iron is much harder and probably more variable in properties than these aluminum, so the results may not be the same.
..................Actually, The holy grail has been to NEVER EVER lap piston and liner together. They are always lapped separately.