This paper discusses the assembly variation that may arise when the positioning between two parts is constrained using a hole and a slot fit over two locators. This method of controlling mating parts is called "positioning". Two parts positioned using a hole and a slot fit over two locators may move relative to each other during assembly because of slight clearances between the locator-hole pair and/or between the locator-slot pair. This relative motion between the parts is called “rattling”. The rattling might be simplified and considered to be small rotations about the locator-hole joint. However, in many cases, equal locator-hole and locator-slot clearances are defined, resulting in more complex motion than simple translation or rotation. This paper derives the radius of a circle circumscribing the rattling area that is obtained by positioning using a hole, slot, and two locators. By determining the radius of the circle circumscribing the rattling area, designers can accurately understand the size of the rattling area and account for it in the design. Furthermore, a comparison will be made with another positioning method using two round holes and two bosses, and the characteristics described. These characteristics are useful for designers when considering parts layout.

This article describes experimental studies using in-situ observation and electric contact resistance method (ECR) on lubrication properties of polyisobutylene (PIB) used as screw tightening lubricant under various surface roughness conditions. The results showed that in the case of surface roughness Ra of 0.011 μm, the separation degree showed 0.87-1 in the test duration, while in the case of Ra of 0.095 μm, the degree decreased over time and reached to zero in the full starvation regime. In addition, wear occurred on the contact area at the condition under low separation degree. It was also found that under the full starvation condition, shear stress was relatively high which corresponded to that in the solid state, and that the stress did not relate with the surface roughness. In the spinning friction test, wear was observed on the contact surface in high surface roughness condition, meanwhile the shear stress was almost similar to that in low roughness conditions. These results reveal that even in high roughness condition, the direct contact occurred on the surfaces was local, and that the solid-like film formed on the surface inhibited significant wear. The lubrication condition in the actual tightening process was also discussed from the results based on this study.