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IntroductionIn order to reduce the wear and to increase then efficiency threads are used in some gears in which there are balls between the nut and the pin threads. For these threaded machines grooves of the same profile cross-section are developed both on the nut and the pin for the balls. The balls do planetary motion along the spiral in the thread, so in addition to their motion component along the longitudinal axis of the thread they work similarly to the balls of the rolling bearings. Also the physical behaviour of the balls and the bearing can be approached according to the theories developed for the ball bearings. Compared to the bearings a fundamental difference is that the balls in the path groove do not return always to the same position but doing a progressive motion as well. In the thread they roll from the start of the thread towards the end of the thread so they enter the grooves and leave them. The aim of the performed tests is to analyse these entering and leaving conditions in function of some geometric characteristics and the load. For the examination we made calculations regarding to the effects of some sizes of the thread on the motion of the balls, primarily analysing what size differences can cause significant force on the balls for entering and leaving the threads. In order to confirm the calculations, measurements were performed to determine the impressing force and the thread torque together for gears of different thread profiles.
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