## 2 Crankshaft Geometry Measuring Methods
Non-reference measurements of large shafts can also be performed on coordinate measuring machines [28; 29; 30; 31], and optical scanners [32; 33; 34] are increasingly used, examples of which are shown in Figure 4.  
Figure 4: Examples of machines used for coordinate measurements of the geometry of large machinery components, including crankshafts: (**a**) Carl Zeiss CARAT UPMC 850 (courtesy of Zeiss); (**b**) Wenzel LH 1512 (courtesy of Wenzel); (**c**) ADCOLE 1200 (courtesy of ADCOLE). Measuring instruments or machines performing non-reference measurements are accurate but are mainly used in laboratories because they require specific measuring conditions, including the accurate, time-consuming centering and aligning of measured items at ambient conditions (temperature, pressure). An additional limitation of these instruments and machines is their high cost, which prevents them from being used to produce small batches of units or in overhaul conditions. The use of these machines will not eliminate the basic difficulties in fixing and supporting large and flaccid components. Attempts have also recently been made to use modern measurement techniques for large crankshafts. For example, the Triton photometric mobile system and a system based on the Atos Trident III optical scanner was used to pre-assess the suitability of a semi-finished product to machine a 40-tonne forged crankshaft with a length of 13 m [35]; however, the use of these techniques is very limited due to their low accuracy. The restriction also applies to the use of other mobile shaft measuring devices (such as measuring arms), which unfortunately have significant uncertainty in their measurements. Taking these restrictions and the recommended accuracy requirements for the measuring equipment into account, this type of device may be used to measure the overall shaft dimensions. By analyzing the measurement techniques for medium and large crankshafts in the conditions present in repair docks and workshops, the most common reference measurement methods are used to locate the shaft in vee blocks. Medium shafts are most often fixed in four vee blocks arranged on a bench plate, as shown in Figure 5.  
Large crankshafts are fixed with multiple vee blocks, and measurements are performed on a specially adapted bench equipped with fixed rigid supports and vee block heads. These supports are anchored to the base with set screws, and the supports can be repositioned by moving them along the main guides of a bed and adapting them to main journals, depending on the shaft design. The shaft geometry is assessed using a series of separate measurements [7], most of which are performed with multi-purpose measuring equipment [36]. The crank web deformation measurements (Figure 6a) are both the basic and final criteria for evaluating the geometry (apart from measurements of linear and angular dimensions, radial, and axial run-out of main journals, the parallelism of main and crank journals, and surface roughness measurements). This is commonly referred to as a springing measurement and is performed using a displacement sensor installed in a special holder [7; 37]. Both the sensor's probe stylus and the holder are equipped with centers, into which the instrument is seated in holes that crankshaft manufacturers pre-drill into the inner faces of individual crank webs. Springing measurements are performed in the vertical and horizontal planes, as the difference between the sensor readings in the two opposite outermost positions of the cranks while the shaft rotates. These extreme positions of the vertical plane are top dead center (TDC) and bottom dead center (BDC), respectively. In the horizontal plane, these positions are called the starboard side (SS) and the port side (PS). Figure 5: Measuring station for crankshafts for medium-speed engines. Assessing a shaft's geometric condition is thus based on indirect measurements.