Selection of Major Locating Surface for Improving Chucking Accuracy

Two different types of surfaces are available as a major locating surface for the chucking of a cylindrical workpiece in turning operation — a flat surface and a cylindrical surface. No systematic study on the selection of a major locating surface has been reported while an appropriate selection considering the geometry of jaws and workpieces results in the significant improvement in the positioning accuracy and repeatability of a range of chucked workpieces. This research covers the most common clamping situation where a cylindrical workpiece is overhung clamped and machined with more than one set-up for finishing. In general, a workpiece with a lower length to diameter ratio should be clamped using an end face as a major locator while using a cylindrical surface can produce better positioning accuracy and repeatability for workpieces with higher length to diameter ratio. Recent studies have demonstrated the benefits of hard turning over abrasive machining processes in terms of surface integrity. A strong need currently exists for improving chucking accuracy since it work a major bottleneck in the implement finish hard turning for the production of precision, load-carrying mechanical components, such as bearings and shafts. This paper presents part of a systematic study on improving chucking accuracy for the implementation of finish hard turning, focusing on the development of criteria on the selection of a major locating surface. First, an analysis on the factors affecting the positioning accuracy for each locating surface is carried out. Then the criteria and guidelines for the selection of a major locating surface were constructed. Finally, systematic experiments were carried out to test the criteria and guidelines. The results showed that the positioning accuracy of the chucked workpieces improved significantly when following the guidelines developed in this study.