# Measuring Procedures for Evaluating the Surface Roughness of Machined Parts
## 3 Experiments
#### 3.2.2 Effect of Cut-Off Filter Setting for Periodic Surface Roughness Profiles  
For the experimental investigation, standard samples of periodic surface roughness profiles (Figure 13) with different \(Ra\) values were selected and processed using the technology (Table 8):  
For periodic profiles (turning, milling, planing), the ISO 4288:1996 standard [34] recommends monitoring the mean spacing of the profile elements \(RSm\) (Appendix A) (ISO 21920-2) [38] as a parameter for choosing the cut-off filter \(Lc\). Here again, the problem arises in that the setting of the cut-off filter \(Lc\) is dependent on the value of the parameter, in this case, \(RSm\), which, however, will only be available as a result of the evaluation of the surface roughness measurement. Standard ISO 4288:1996 presents a table of recommended values of section length or filter cut-off according to \(RSm\) values (Table 9). The results for individual technologies for periodic profiles (Appendix C) were subjected to the above analyses, and the optimal setting of the cut-off filter \(Lc\) for each technology was determined. Figure 15 shows a comparison of the selection of the filter cut-off value \(Lc\) for periodic profiles with the recommendations for the selection of the filter cut-off value \(Lc\) according to ISO 4288/1996 [34]. Figure 12: Optimal setting of the cut-off filter \(Lc\) for tested reference samples of non-periodic profiles and setting recommended by standards [33; 34; 35; 36; 37; 38; 39; 40; 50; 51; 52; 53; 54; 55; 56; 57; 58; 59; 60; 61; 62; 63; 64; 65]. Figure 13: Etalon samples of surface roughness—milling operation, turning operation, and planing operation. Samples produced by both methods of milling (Figure 15) are in accordance with the recommendations of the mentioned ISO standard. For the turned and planed samples, slight disproportions are visible in the intervals suitable for the free cut-off values of the \(Lc\) filter; however, these interval shifts may be related to measurement uncertainties. The analysis of surface roughness profiles, \(RSm\) values, and \(Ra\) values reveals the interesting fact that for all samples of periodic roughness surfaces, it is advisable to proceed in such a way that to determine the parameter \(RSm\), it is advisable to carry out measurements at all settings of the cut-off filter \(Lc\) (similarly to what was carried out in the case of \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Samples: Turning** & **Sample 1** & **Sample 2** & **Sample 3** & **Sample 4** & **Sample 5** \\ \hline Nominal value \(Ran\) (\(\mu\)m) & 0.8 & 1.6 & 3.2 & 6.3 & 12.5 \\ \hline Nominal corrected \(value\)\(Ra\) (\(\mu\)m) & 0.784 & 1.55 & 2.78 & 6.55 & 12.63 \\ \hline
**Samples: Slab Mill** & **Sample 1** & **Sample 2** & **Sample 3** & **Sample 4** & **Sample 5** \\
**Sample Set: 2580663** & & & & & \\ \hline Nominal value \(Ran\) (\(\mu\)m) & 1.6 & 3.2 & 6.3 & 12.5 & 25 \\ \hline Nominal corrected \(value\)\(Ra\) (\(\mu\)m) & 1.52 & 3.57 & 6.05 & 10.25 & 16.25 \\ \hline
**Samples: Face Mill** & **Sample 1** & **Sample 2** & **Sample 3** & **Sample 4** & **Sample 5** \\
**Sample Set: 2580663** & & & & & \\ \hline Nominal value \(Ran\) (\(\mu\)m) & 1.6 & 3.2 & 6.3 & 12.5 & 25 \\ \hline Nominal corrected \(value\)\(Ra\) (\(\mu\)m) & 1.71 & 3.46 & 6.17 & 11 & 19.25 \\ \hline
**Samples: Flaning** & **Sample Set: 580845** & **Sample 1** & **Sample 2** & **Sample 3** & **Sample 4** & **Sample 5** \\ \hline Nominal value \(Ran\) (\(\mu\)m) & 1.6 & 3.2 & 6.3 & 12.5 & 25 \\ \hline Nominal corrected \(value\)\(Ra\) (\(\mu\)m) & 1.5 & 3.04 & 6.57 & 11.5 & 20.25 \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Selected evaluated periodic profile samples.