Gyro finishing is a mass-finishing process in which fixed workpieces are finished by contact with the flow of abrasive media owing to the rotation of the barrel. The process is used to finish large complex-shaped workpieces, such as large gears and parts constructed using additive manufacturing. In our previous study, we proposed a cover plate positioned above a workpiece to restrict the upward motion of abrasive media after contact with the workpiece, thereby improving the finishing speed. In this study, plates were added at the side of the workpiece to restrict the flow of the abrasive media toward the side of the workpiece and further improve the finishing speed. First, we evaluated the effect of the side plates using a simple-shaped workpiece. The difference in the surface roughness during a 5 min process was evaluated under certain conditions of the side cover plates. We confirmed that the finishing speed can be increased by using a side cover plate whose front was positioned behind the workpiece center because of the restriction of motion of the abrasive media. In contrast, the finishing speed decreased when a side cover plate whose front was positioned in front of the workpiece center was used because of the interruption in the transmission of force from the barrel wall to the abrasive media near the workpiece, owing to the side cover plates. Subsequently, the effect of the side cover plates placed at a suitable position was evaluated based on variations in the surface roughness during the process. We confirmed that the finishing speed increased by approximately a factor of 1.5 when the side cover plates were used owing to restrictions in the motion of the abrasive media. Finally, a spur gear was finished with cover plates, as a sample of practical workpieces. The finishing speed was determined based on the difference in the surface roughness of the gear teeth during the process. The finishing speed increased when a side cover plate whose front was positioned behind the workpiece center was used. Therefore, it can be concluded that the use of side cover plates is an effective technique to improve the finishing speed in gyro finishing.

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