## 2 Crankshaft Geometry Measuring Methods
Springing measurements are the final criterion for assessing the shaft geometry, since it is not possible to directly measure journal axes' shape deviations and positional deviations. When the shaft is supported on several fixed, rigid vee block supports, it is difficult to eliminate a shaft's elastic deformation due to pre-deflections and geometric deviations. This results in geometric deviations that are conjugated with and interact with elastic deformations, making them virtually impossible to eliminate. In addition, conventional springing measurements suffer from a lack of permanent measurement means. In this case [7], the results are interpreted by assuming that the crank web deformations are symmetrical with respect to the main axis of a crank (Figure 6b), which is not always the actual case [38; 39]. This assumption follows from the principle of measurement, as the sensor measures the total deformation of crank webs, which often results in the misinterpretation of measurement results. However, contrary to the previous remarks, this type of measurement is now commonly used to verify and assess shaft geometries, and crankshaft manufacturers use it at individual stages of interoperational inspection and in the final assessment of the shaft geometry. Repair shops and docks also use this type of assessment under operating conditions to measure the accuracy of the shaft bearing in the engine body. There are a number of scientific papers tackling the issues of appropriate bearing alignment [40] and identification of dynamic bearing parameters [41; 42; 43]. In our paper, we tackle quasi-static conditions during geometry measurement. Figure 6: Crank web deformation measurements: (**a**) view of the instrument; (**b**) interpretation of measurement results. The procedures for measuring large crankshafts show significant limitations concerning the comprehensive measurement of geometric deviations, especially those in the shape and the position of axes [5]. These procedures are based on outdated measurement techniques, whose accuracy has not been adjusted to match the increasing manufacturing precision expected of modern crankshafts. Significant progress has been made in this type of measurement, as the discussion of current issues was narrowed to measuring deviations and shape profiles of cylindrical surfaces of shafts (main journals, crank journals). Particularly worth noting are the effects of works carried out at the Kielce University of Technology. This resulted in the development and implementation of an industrial-grade measuring system using a MUK 25-600 head and SAJD software to measure deviations and roundness profiles of large cylindrical machinery components (Figure 7) [23]. Measurements are performed by the reference method when using this system. The MUK 25-600 head, equipped with an induction displacement sensor, is mounted directly on a cylindrical surface. The measuring head is connected to a computer with SAJD software, which transforms the measured profile into an actual transformed profile. This approach enables the reference method to be applied to the measurements performed by non-reference methods, i.e., those whose results can be obtained using precise but expensive measuring machines. The resulting, digitized actual profile can be presented in either a polar or Cartesian coordinate system. The profile is defined by \(n_{\!f}\) harmonics (\(n_{\!f}\)\(\in\)\(\langle 2\div 15\rangle\) or \(n_{\!f}\)\(\in\)\(\langle 2\div 50\rangle\)) and includes some surface waviness components. The basic version of the program allows the roundness profile to be assessed using roundness deviation \(\Delta Z\) and the amplitude of the largest harmonic \(C_{k}\) to present the profile as an amplitude spectrum. The extended version of the software enables a complete assessment of the roundness profile in accordance with the ISO standard by selecting the appropriate filter and reference circle and by determining any profile assessment parameter.