Power Required to Drill Cast Iron and Steel

Abstract This paper presents the results of drilling tests on cast iron and steel. Drills ranging in diameter from 1/2 to 1-1/2 in. of the standard twist-drill type were used. The drills were considered sharp in all tests. A coolant consisting of one part of soluble oil and 16 parts of water was used in all tests. The materials cut consisted of one regular machining cast iron and one cast iron made up of 20 per cent charcoal pig iron, together with 17 steels of a wide variety of chemical analyses, which were selected to cover the steels commonly used in modern manufacture. Data as to drilling torque, thrust, computed horsepower at the drill point, and net horsepower supplied to the machine as measured on a recording wattmeter are given under two headings: commercial tests and special tests. All commercial tests were run at a peripheral speed of the drill of approximately 60 ft. per min. The feed for each drill size was as near to those given in the usual commercial-drilling table as the change gears available would permit. They were as follows: 0.009 in. per rev. feed for the 1/2-in. diameter drill, 0.011 in. for the 5/8-in. drill, 0.012 in. for the 3/4-in. drill, 0.013 in. for the 1-in. drill and 0.015 in. for the 1-1/4- and 1-1/2-in. diameter drills. Special tests were run on various cast irons and steels so that the influence of the speed, feed, and drill diameter could be determined, in order that the results of the commercial-drilling tests could be extended to cover any other conditions of drilling for each material. It was found from these special tests that the thrust for both cast iron and steel increased in direct proportion to the drill diameter d; that the torque increased in proportion to d2 for cast iron and d1.8 for steel. The thrust increased with an increase in feed f, but at a rate as slow as f0.6 for both cast iron and steel. The torque increased as f0.6 for cast iron, but f0.78 for steel. It was found that the torque and thrust remained practically constant over the whole range of speeds covered from 74 to 441 r.p.m. for each drill size and feed. An attempt is made to correlate the hardness values of the materials determined by the Brinell, Rockwell, scleroscope, and Herbert pendulum hardness testers, with the results obtained from the drilling tests. It is concluded that no satisfactory relation exists between these properties.