## 1 Introduction  
Over the past decade, additive manufacturing (AM) has gained increasing popularity within the engineering community. This manufacturing technique allows for the production of complex shapes, primarily employed as structural or design components in machinery. However, when it comes to bearing components, particularly kinematic joints, traditional metallic machined parts are still predominantly utilized. The primary objective of this research paper is to investigate the viability of employing 3D-printed gear bearings under various conditions of radial loading values and rotational speeds for machinery applications. In the course of this study, we introduce a failure criterion and provide an estimation of the operational lifespan of such bearings within the specified loading conditions. It is important to note that this gear bearing is not assembled but rather created as a single, integral piece directly by the 3D printer. This paper addresses a relatively unexplored area within machinery construction, involving the utilization of polymer additive manufacturing techniques for bearings. Traditionally, to make rotational or translational joints for 3D-printed elements, metallic bearings are used because of their endurance and low friction characteristics, and these are inserted into the 3D-printed elements. This is a good system if metallic bearings are available, but an alternative could be to use 3D-printed bearings in the situation in which access to classical bearings is difficult, or the application areas require non-metallic components, such as inside a magnetic resonance imaging device. Gear bearings are a rather new concept, but their main function is to allow for rotating motion between two elements with low energy loss due to friction, similar to traditional plain and rolling element bearings. From the point of view of geometrical configuration, gear bearings are rolling element bearings in the sense that the gear elements, similar to balls or rollers, have rolling motion relative to the central gear or the outer geared cage, but their behavior is different when manufactured using the FDM process. Our experience with 3D-printed rollers or ball bearings is that they tend to get stuck and stop rolling due to manufacturing imprecisions, thus transforming the rolling motion into a sliding motion. This is the case also when a cage is present in the roller bearings. Gear bearings, on the other hand, are less sensitive to manufacturing imperfections, and the rolling motion is not affected. Also, they also do not need a cage for gear spacing, since the distance between gears is retained due to the teeth meshing. In this paper, for the manufacturing process, we used the common FDM process, and the resulting gears do not have a very smooth surface. Still, the performance at low rotational speeds and loads is promising. The origins of gear bearings come from developments at NASA in the 2000s [1; 2]. An example gear bearing is presented in Figure 1. It is similar to a planetary gear setup, where the gears have taken the place of the balls in a ball bearing or in a cylindrical bearing. The gears have a herringbone shape, and the whole bearing is printed in one piece together. This configuration does not allow the gears to slide past each other; thus, the gear bearing can take limited axial loads. Another feature is that it does not require a cage to keep the rollers spread apart, because the gears keep them spread apart. An early pioneer of this type of setup is [PERSON], who in 2013 published a video on YouTube in which he presented a 3D-printed gear bearing. An extension of this gear bearing is that one can put two such devices side by side, connect the planet gears together and obtain a very high transmission ratio and a robust planetary gearbox, with applications in robotics [1; 3], medicine [4], aeronautics or space applications [5]. There are a number of parameters that influence the mechanical properties of additive manufactured parts, especially additive manufactured gears.