# Measuring Procedures for Evaluating the Surface Roughness of Machined Parts
## 3 Experiments  
Quantities of surface roughness are precisely defined in the standard, but obtaining the correct value of these quantities by measurement depends on the correct choice of measurement parameters. These include cut-off filter settings, evaluation standards, number of section lengths, and measuring speed. Important factors to consider when assessing surface roughness using a stylus-based surface roughness tester:  
* The size of the measured irregularities must be appropriate to the measuring range of the sensor (vertical stroke); irregularities exceeding its size of the maximum value of vertical lift cannot be measured. * The set value of the sensed length should include 5--a multiple of the section length plus the start-up and run-down path of the sensor; if it is not possible to meet this requirement (e.g., due to the size of the measured area), it is necessary to take into account that the result of the measurements will be affected by the failure to meet the requirement. * The object to be measured must be clamped, orientated spatially, and the sensor must be placed appropriately on the measured surface; for this, it is necessary to choose the appropriate shape of the sensor with regard to its diameter, length, the possibility of fitting the bottom of the groove, the possibility of measuring on roundness, etc. ; in case of inadmissibility of the place of measuring the surface roughness of the profilometer  
Figure 5: Cumulative standard deviations for 100 measurements at the same place under unchanged conditions (measured to standard—ISO 1997 [33]; 0.25 mm/s; \(Lc=2.5\) mm; \(X=5\); Gauss). sensor, replicas (imprints) of irregularities can be used in plastic film (or other suitable material) and the profile of the irregularities can be taken from this film (negative of the irregularities). * Corresponding working conditions must be set, including measuring range, sensed length, filter type, basic length (cut-off) of the filter, and speed of the probe. The measurement conditions during the measurements were as follows:  
The surface tester was equipped with a stylus with a sliding tip. The tip of the stylus rides in a line across the surface, moving vertically over the peaks and valleys of the evaluated surface. Changes in the stylus' height are registered electrically and tracked against the position as the stylus moves, creating a measured profile. The shape of the stylus is conical with a spherical tip with a radius of 2 \(\upmu\)m and a tip angle of 60\({}^{\circ}\), and it is pressed with a measuring force of 0.75 mN. The skid force is less than 400 mN. The cone angle and tip radius determine the smallest features that a stylus can trace. The relative humidity was in the interval (65 \(\pm\) 5)%, and the temperature was \((20\pm 2)\)\({}^{\circ}\)C.  
The measurement methodology encounters several problems that need to be defined--here, it must be remembered that even the setting of the measurement conditions can have an impact on the result of the evaluation of the arithmetical mean deviation of the assessed roughness profile. It is, therefore, necessary to give an answer to the question of what this effect is and how to choose individual measurement conditions when assessing surface roughness. The following measurement conditions are investigated:  
* Choice of cut-off filter \(\lambda c\) (or textual equivalent \(Lc\)): 0.08 mm; 0.25 mm; 0.8 mm; 2.5 mm; 8 mm (the surface tester, which is available for experiments, does not have the setting of the value \(Lc\) = 8 mm). * Choice of standard for evaluation: ISO 1997 [33; 34; 35; 36; 37; 38; 39; 40], JIS 1982 [50], JIS 1994 [51], JIS 2001 [52; 53; 54; 55; 56; 57; 58], ANSI Gauss [59; 60; 61; 62], ANSI PC 75 [63; 64; 65], VDA, [63; 64; 65]. * Selection of speed of the sensing tip (stylus): 0.25 mm/s; 0.5 mm/s; 0.75 mm/s.