Removal machining cannot generally fabricate a hole on the inside wall of another hole. That means, removal machining has the limitation for its fabricatable hole shape. The limitation affects designs of machines. In particular, the design of pipelines built in hydraulic equipment is affected. Many research groups have conducted the studies to overcome the limitation. Our research group had also developed the devices which can create such holes by means of electrical discharge machining in the previous studies. The previous studies had made it obvious that the devices can create a hole of 3.1 ~ 15.4 mm in inner diameter inside another hole of 21 mm. However, such a hole with an inner diameter less than 3.1 mm cannot be created. So, all the problems in designing pipelines built in hydraulic equipment are not solved. Therefore, this study has proposed a new device which can create a thin hole inside another hole. As a consequence, a hole of 1.7 mm / 0.6 mm in maximum / minimum inner diameter and of 26.0 mm in length could be created. This proves that the newly developed device has the ability to create thin holes on the inside walls of another holes.

Recent ball screw is applied for power transmission such as an injection press machine. A ball screw is inept to power transmission due to strengthening the contact surface pressure between the ball and the thread groove. However, an instantaneous large load is required in mold clamping. Therefore, ball screw mechanism is applied owing to its high responsibility. Though a manufacturer of ball screw takes measures for upgrading the axial load capacity and rigidity, the form of thread groove remains in symmetry. Restricting the intended purpose to injection molding machine, a large force should be loaded to the mold clamping direction, but any axial force is not required in return. There is an angular ball bearing or a buttress thread as mechanical components with which a large unidirectional force can be applied. Thus, the authors considered that a large unidirectional (axial) force can be loaded with forming the thread groove asymmetric like the angular ball bearing. In this research, an experimental product was made using 3D metal printer. Then, it was confirmed that a ball screw having asymmetric thread groove was imaginable in mechanism and the axial rigidity became higher by increasing the contact angle. According to the results, the authors verified the improvement of axial rigidity by processing the thread groove of existing ball screw to asymmetric form.

In the previous paper, the authors had reported a current situation survey of dynamic torque for small ball bearing. It was made clear that the torque didn’t become constant, and the variation was large even if sixteen bearings (608) of each different multiple manufactures were applied in one hour measurement time. On the other hand, the average values for the sixteen measured values of each manufactures intended to decrease with a lapse of time. A reason why the torque variation was large can be a brevity of measurement time. Therefore, in this study, the measurement time was set to twenty-four hours, and a dependence property of torque for measurement time was clarified. Consequently, when the rotational speed was high, the torque reflected the trend of stabilization of torque. However, when the rotational speed was low, the torque was not convergent after twenty-four hours running.