Abstract: Taking the process of precise boring ofΦ16 mm holes on rocker arm support as an example, this process not only ensures the accuracy of holes, but also the accuracy of holes and reference dimensions A and B. A new type of positioning pin is proposed, which can replace the traditional diamond pin. The pin is edged by conical pin, and a spring mechanism is added at the bottom of the pin. The elastic force of spring is used for floating positioning to ensure the floating tapered edge pin. Contact with the zero clearance of the hole, thereby eliminating the pinhole clearance and improving the fixture positioning accuracy. If the conical floating edge-cutting pin can propel smoothly into the workpiece hole under the elastic force of the spring, it is necessary to ensure that the workpiece and the pin can not appear self-locking phenomenon in this process. Through the force analysis and calculation of the workpiece, a reasonable taper is selected to eliminate the self-locking phenomenon. The conical floating edge-cutting pin has no requirement for the accuracy of positioning hole, but its positioning accuracy is higher than that of the traditional cylindrical edge-cutting pin, which can replace the role of cylindrical edge-cutting pin in fixture.