Fatigue strength improvement in roller chain due to press fitting between pin and outer plate and between bush and inner plate

•Fatigue strength improvement due to press-fitting for roller chains.•Effects of press-fitting ratio and scratch like damage.•Proposal of small press-fitting ratio for improving manufacturing efficiency.•Validity of the newly defined nominal stress for roller chain design. The press-fitting effect on the fatigue strength is studied experimentally with FEM for the plate/pin and for plate/bush since they control the whole strength of the roller chain. The results confirm that a relatively smaller press-fitting ratio is useful for improving the fatigue strength efficiently since it is highly productive. This observation suggests that if the damage caused by the currently used press fitting can be prevented, the fatigue strength of real roller chains can be greatly improved by increasing the fitting ratio. A newly defined nominal stress definition is proposed and confirmed to be useful for machine design.