Optimisation of factors influencing the efficiency of finish machining operations

Optimum machining conditions were determined for various materials, steels, cast irons, brasseses, bronzes and an aluminium alloy. Surface finish readings were taken with the Sigmatex and the Surtronic and values of 10 micro-in and below were obtained at 0.001 ipr feed both under dry and wet conditions. The tests were extended to higher feeds, the maximum being 0.004 ipr; at this feed, the surface finish fell, in most cases, below 20 micro-in. it was found necessary to use high cutting speeds of the order of 800 to 1000 fpm in most cases. The most efficient tool used was a Titanium Carbide which successfully machined the whole range of test materials. The factors which were found to discourage the production of a good surface finish, given the right feed and speed, were scratching of the chip on the finished surface, bad blending of the nose radius with the two cutting edges, wrong order of grinding the flank clearance faces and the top rake face. The factors which encouraged a good surface finish were the choice of the right tool material, a suitable facet or chip deflector.