Abstract: A lubricant is supplied to a bearing for a rotary shaft by an oil pump capable of discharging the lubricant at different flow rates depending upon its speed of operation. The oil pump is preliminarily operated to allow the user to derive and determine a relationship between temperature rise in the bearing and the flow rate of the lubricant by the oil pump with rate of rotation of the shaft as parameter. An optimum flow rate at which the temperature rise is minimized can be determined from such a relationship. The oil pump is operated such that the lubricant is discharged at this optimum flow rate and according to the current rotary speed of the shaft. Corresponding to different rotary speeds of the shaft, a temperature characteristic curve representing these optimum flow rates of the lubricant can be obtained, and this temperature characteristic curve may be used to vary the speed of operation of the oil pump to change the flow rate of the lubricant according to different rotary speeds of the shaft.

Abstract: A rotary boring machine comprises a base machine placed on the ground, a boring drill provided with the base machine and driven for rotation, a dip gauge provided at the tip end of the boring drill, a first circuit provided in an intermediate portion of the boring drill and electrically connected to the dip gauge for producing a varying flux corresponding to the output signal of the dip gauge, and a second circuit provided in the intermediate portion of the boring drill in opposition to the first circuit and inducting an induction current corresponding to the output signal of the dip gauge through an electromagnetic induction caused by the varying flux generated by the first circuit. The output signal of the dip gauge is transmitted by electromagnetic induction between the first and second circuits and thus transmitted to the base machine without requiring physical connection of the signal transmission lines.