# Measuring Procedures for Evaluating the Surface Roughness of Machined Parts
## 1 Introduction  
Surface roughness is a key parameter in many industrial devices and significantly affects the quality and equipment composed of several machined components; therefore, reliable measurement of surface roughness plays a fundamental role in ensuring the functionality and reliability of the final product. However, the measurement of surface roughness is not without problems, especially when it comes to quantifying the uncertainty associated with these measurements. This estimate of uncertainty is necessary to evaluate the reliability and comparability of the surface roughness data and, to the same extent, the measurement surface roughness data obtained. There are several measuring methods and devices for investigating surface roughness, and generally, we can categorize them into two main groups, contact and non-contact methods and devices. There are a number of devices available for evaluating surface roughness, and they are probably best divided according to individual methods of measuring and evaluating surface roughness. The device for contact stylus-based contact measurements is one of the most widely used methods for measuring surface roughness, where the contact stylus profilometer is probably the only representative. The disadvantages of the contact-based measurement include mainly the stylus tip wear caused due to the contact between the sharp tip of thestylus and the surface roughness. The sample's surface will be scratched because of the movement of the stylus tip on the surface during the measurement, and the measurement is limited to the radius of the stylus tip. Devices for non-contact methods of assessing surface roughness are more expensive. There are many devices and methods for non-contact methods, such as laser triangulation, optical interferometry, confocal microscopy, and atomic force microscopy, which is the most accurate of these methods. The scan quality of these measuring instruments is mainly dependent on the optical properties of the materials tested. One of the common methods for determining surface roughness is the contact pen method or stylus profilometers, which provides relatively quick measurement results at a favorable price than other methods that require relatively expensive equipment. For production practice, the contact method is thus an ideal tool for evaluating the surface of machined parts, but this contact method is associated with a number of problems because the very implementation of this method depends on the correct setting of the measurement conditions and the correct implementation of the measurement and evaluation of surface roughness values. Experience from different experiments and work with this contact method shows that inappropriate setting of the wavelength limit, also known as cut-off, inappropriate stylus speed, and inappropriate standard for evaluation, causes diametrically different results of surface roughness assessment and thus, the whole process of surface roughness assessment is then completely devalued. Another task is to understand and quantify the uncertainty of the measurement and evaluation of surface roughness values for each instrument quality, calibration standards, measurement conditions, and the way the surface of the part is produced, which can significantly validate the results and evaluations. For common practice, it is necessary to create a methodology for the optimal process of evaluating the surface of machined parts and determining the measurement uncertainty estimate. In this article, we will delve into the topic of surface roughness measurement with a focus on the methodology of implementing the contact method and determining the estimate and evaluation of measurement uncertainty. Investigating and understanding specific issues is important to the operator in obtaining reliable results from the surface roughness evaluation process.