## 1 Introduction  
When manufacturing mechanical transmissions, special attention is paid to the accuracy and quality of the surfaces of the parts directly engaged in the transmission of speed and efforts. The accuracy of these parts must be high and the roughness of their contact surfaces must be low [1; 2; 3; 4; 5; 6]. In practice, in general engineering, these structural elements are manufactured with the accuracy of contact surfaces according to the 7 th tolerance grade, which ranges in the interval from 0.025 to 0.057 mm (depending on their size). At the same time, the roughness of the contact surfaces is brought to a level in the order of Ra 0.8-1.6 \(\upmu\)m. The shape of the cycloid profile of the tooth also influences the working capacity of the mechanism in both longitudinal [7] and transverse [8; 9] directions. The cycloid profile modification allows errors to be compensated for in the geometry of the cycloid engagement and the power characteristics to be enhanced [7; 10]. In particular, authors [7] note that, when correcting the cycloid profile, the contact voltage changes on average by several tens of megapascals. These design requirements cause certain technological challenges and increase the manufacturing time of such parts. At the same time, a decrease in the accuracy of manufacturing parts leads to a quality deterioration of the mechanism and loss of its accuracy characteristics due to emerging manufacturing clearances [11]. Therefore, the study of the possibility for lowering the manufacturing accuracy of the contacting surfaces of disks engaged in a cycloid transmission, while maintaining the accuracy of the transmission itself, is a vital task. The solution to this will allow a decrease in the manufacturing time of such parts and a reduction in the cost of the entire mechanism. The accuracy of the transmission mechanism, among other things, is influenced by such a characteristic as the clearance in the engagement (angular play) [8]. In [8], a method for modifying the cycloid tooth profile is considered, taking into account the clearances in the engagement, but the influence of the manufacturing accuracy of the cycloid profile has not been analysed. The clearance in the engagement can be designed in, when designing the transmission and it also definitely emerges when manufacturing the transmission links, being directly in the engagement. The structurally laid clearance is calculated and can be adjusted when assembling the transmission. Additionally, the manufacturing clearance, that is emerging due to dimension deviations from the absolute value when manufacturing parts, is difficult to take into account owing to the probabilistic obtainment of dimensions during manufacture. At the same time, there are transmissions, for which the clearance adjustment in the engagement is not provided because the design does not allow it. Such transmissions are cycloid pinwheel [8; 9] transmissions with intermediate rolling elements (IRE), in general [12; 13; 14; 15], and transmissions with intermediate rolling elements and a free cage (IREFC) [16], in particular (Figure 1). In IREFC transmissions, the loaded parts are cam 1, rolling elements 2 and ring 3 (Figure 1). The accuracy of the manufacturing of these parts influences the engagement quality. There is also a separator 4 between the cycloidal profiles of cam 1 and wheel 3. However, the manufacturing accuracy will not affect the accuracy of the engagement of transmissions with IRE. This is explained by the fact that a separator 4 is only used for the distribution of the rolling elements 2 on a mutual angular placement and it keeps them from moving into the root of the cycloidal profile (for example, the cam) when they are not under load. The standard technology for manufacturing the separator allows the obtainment of such a thickness of the part that it will not worsen the engagement in any case. Cycloid pinwheel transmissions are designed so that the clearance between the cycloid profiles and the pin is not regulated.