Drilling Characteristics of a Small Electrodrill

Abstract

Drilling experiments are made with a 3.7kW electrodrill, using corn, blade and diamond impregnated bits, respectively. Sandstone, tuff and andesite of which compressive strengthes are from 200 to 800kg/cm2 are drilled by these bits. Rotating speeds are between 690 and 740 rpm depending upon bit weight which is ranged from 40 to 300kg. In these experiments following conclusions are obtained:1) A cone bit is the most favorable for the electrodrill, because it gives a high drilling rate and a low torque.2) The electrodrill can not give a high bit weight, and this causes a low drilling efficiency. Notwithstanding a low efficiency of the electrodrill, it can drill comparatively fast, because its rotating speed is high.3) Three means are proposed to increase the drilling efficiency of the electrodrill: 1) to increase the output of a motor in order to give a higher bit weight, 2) to reduce the rotating speed to a reasonable level, and 3) to use a proper bit specially designed for the electrodrill.