Self-centering positioner and principle for locating and guiding deep-hole drills using oil films

摘要

A novel principle for machining of deep holes is proposed. A self-centering positioner (SCP) was invented, and the principle for locating and guiding deep-hole drills using oil films was studied. The SCP is fixed between the drill tip and the drill shank. Four wedge-shaped zones are formed between the SCP and the wall of the machined hole. The rotating SCP draws cutting oil into the converging, wedge-shaped zones, which produces a pressure in each wedge-shaped oil film. The oil films will support, locate, and guide the SCP along with the drill tip and the shank. The oil films act on the SCP in a manner similar to that by which a four-jaw chuck clamps a workpiece, thereby enhancing the stiffness of the drill system and protecting the drill from deviation. The force exerted on the SCP by each oil film is calculated. Experiments showed that hole straightness was improved when using an SCP. The eccentricity ratio and width of the SCP strongly influence the force exerted on the SCP and straightness of the hole. A deep-hole drill with an SCP follows the axis of the hole during the machining process-in contrast to the current method in which the drill is guided by the wall of the hole. This novel principle applies to both symmetric and asymmetric deep-hole drills. It is derived from dynamic lubrication in bearings and serves as a break from the convention that has guided deep-hole machining for many years.