Abstract
Turning and drilling tests have been carried out on nine different materials.
The most critical factor in turning is the breakouts at the corners of the test-specimen, especially at low densities. These can be eliminated by adopting a lower feed and smaller depth of cut. The best surface finish is achieved with the highest possible speed and low cut depth. Alloying iron with 0·5% sulphur resulted in the lowest recorded specific cutting force, a good surface finish, and the longest tool life attained. The density had no influence on the tool wear.
Tool life in drilling can be improved considerably by using: (a) a 40° helix angle for soft power-metallurgy materials; (b) extra-short drills. Burrs can be eliminated by shortening the chisel edge or increasing the point angle to 185°. The use of sulphur-alloyed iron resulted in a tool life many times higher than that for plain iron of the same density.
Machining recommendations are given for turning and drilling the various materials.
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