This paper focuses on the development, calculation, and production of a device designed for testing welded joints through bending. The primary objective of this paper is to address the need for reliable certification of welders responsible for welding critical components. The paper begins with a thorough analysis of the structural design, shafts, and bearings, which are key components of the testing device. Various calculations are conducted to ensure the strength and functionality of the device, taking into account factors such as load capacity, stress distribution, and material properties. During the design and production phases, several challenges arise and are carefully examined. The paper delves into the complexities encountered during the device's construction, as well as the manufacturing process. By identifying and analyzing these issues, practical solutions are proposed, contributing to overall improvements in device performance and efficiency. The development of the testing device is the result of collaboration with the company POLIROL d.o.o. The project originated from their need for welder certification, as their welders are responsible for joining critical components that directly affect the functionality and safety of bridges and expansion joints. In conclusion, this paper provides a comprehensive overview of the design, calculation, and production process of a device for bending welded joints. By addressing the challenges encountered during development, this research contributes to improving the reliability and accuracy of welder certification, ultimately ensuring the quality and durability of welded connections in critical infrastructure projects.