# Measuring Procedures for Evaluating the Surface Roughness of Machined Parts
## 2 Methodology  
Surface roughness is a geometric property of the surface, and there are no direct methods to measure it. Surface roughness has a decisive influence on the coefficient of friction of contacting surfaces, on adhesion between surfaces, and various other properties and phenomena; it also has direct effects on the material properties of components [25; 26; 27; 28; 29; 30; 31; 32] but also has a key role in other areas, where it significantly affects the function of various devices. Terminology according to the standards and used methods of measurement and data processing is processed in Appendix A. Profile curves are usually measured, and appropriate characteristics and quantities are evaluated from them, which are considered criteria for assessing surface roughness. Surface roughness parameters and values are defined in standards EN ISO 4287 and EN ISO 5436. These standards were later replaced by standards ISO 21920-1, ISO 21920-2, ISO 21920-3 [33; 34; 35; 36; 37; 38; 39; 40]. Current engineering practice is characterized by an increase in requirements for precision and reproducibility of production in the period of production of sophisticated production. The optimal quality of the surface of the parts is one of the prerequisites for the correct function of products (machines, devices, tools) and significantly affects the service life of the parts and even the entire machines. The roughness of the surface represents a collection of irregularities with relatively small distances from a perfect and ideally smooth surface, while these irregularities arise as a result of the used production technology or wear due to use (STN ISO 4287, ISO 21920-1, ISO 21920-2, and ISO 21920-3) [33; 34; 35; 36]. In the following sections, we will distinguish the so-called periodic and non-periodic surface roughness profiles (for more details, see Appendix A). The ISO 21920-3 [39] standard introduces no distinction between periodic and non-periodic profiles compared to the edition of ISO 4288:1996 [34]. Nevertheless, the following part is focused on the analysis in the course of the choice of cut-off filter for individual technologies, which were used to produce individual samples. Just like the other methods, the stylus-based method encounters a whole range of limiting factors that result mostly from the requirements of its specific implementation, and sometimes there are conflicting requirements that require a compromise solution. This method makes it possible to determine the numerical values of normalized and non-normalized characteristics of surface roughness and then use them for the most modern statistical and spectral assessment of surface unevenness. The implementation of this method is ensured by the stylus-based surface roughness tester, which consists of a mechanical and electronic part (Figure 1), while the mechanical deflection, generated by the sensing tip, which monitors the surface irregularities of the measured surface, is transformed into an electrical signal in the induction position transducer, which it is further processed and interpreted as a numerical value of the selected surface roughness characteristic, or as a graphic record of the profile of surface roughness. A touch profilometer is a contact profilometer that brings the stylus tip into direct contact with the measuring surface and tracks or moves along a desired path to determine the topography of the surface. The working principle of a touch profilometer is to analyze the topography of a surface using a probe that physically moves over the surface to obtain surface properties such as height. An unspecified (due to commercial reasons) stylus-based surface roughness tester was used for experimental measurements. The device allows you to set four different values of the cut-off filter parameter (0.08 mm; 0.25 mm; 0.8 mm; 2.5 mm). However, the manufacturer of the surface tester does not define the maximum permissible error or measurement uncertainty, so it is necessary to determine this uncertainty in some way for measurement purposes.