Back when headsets were loose ball angular contact things some cup/cone missalignment could be tolerated. These days what with cartridge bearings (and the tiny balls found in them) facing alignment is more vital. That said I sometimes do an initial facing with a hand file and a square. (But this is with a constant diameter HT). When I reface with the proper cutter the hand jobs have shown to be pretty close, minimal high spots being initially cut. Andy