The Torque and Thrust of Small Drills Operating in Various Metals

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Abstract
This paper presents the results of a detailed study in which torque and thrust were recorded when drilling with small drills ranging from 1/8 in. to 1/2 in. in diameter. The influence of cutting speed on the value of torque and thrust when cutting a low-carbon steel with a 1-to-16 emulsion is shown to be appreciable at the lower speeds but negligible in the higher ranges of speeds. The torque and thrust values are shown to be reduced slightly for increased values of helix when drilling low-carbon steel with drills of 5/32 in. diameter having helix angles ranging from 21 to 40 deg. It is shown that the greatest factor of safety, as represented by breaking strength over operating torque, is obtained when the helix angle is about 36 deg. Another series of tests reported in this paper shows that the torque and thrust are increased as the web thickness of 23-deg helix drills of 5/32 in. diameter is increased from 0.029 to 0.043 in. The factor of safety is reduced as the web thickness is increased. Extensive data for torque and thrust for drill sizes ranging from 1/8 in. to 1/2 in. are given when drilling nine ferrous and nonferrous metals. These data are then correlated with corresponding torque and thrust values for the same metals previously reported (1, 2, 3,) for larger diameter drills.

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