# Measuring Procedures for Evaluating the Surface Roughness of Machined Parts
## 3 Experiments
The Influence of the Cut-Off Setting on the Evaluation of the Arithmetic Mean Height of the Roughness Ra  
According to the cut-off value \(\lambda\)\(c\) (or the text equivalent \(L\)\(c\)), the recommendation is also for the choice of the second parameter cut-off \(\lambda\)s (or the text equivalent \(Ls\)) according to Table 2 [ISO 11562; ISO 3274] [35,40]. Both values must be set before measuring the assessed surface of the component. This applies except for the VDA [63; 64; 65], JIS1982 [50], and JIS1994 [51] standards, where this parameter is not used. When choosing the parameters of the cut-off filter, the parameters of the stylus tip must also be taken into account. The recommended combinations of \(\lambda\)\(c\), \(\lambda\)\(s\), and stylus tip radius are shown in ISO 3274:1996 [35]. The used roughness gauge has a stylus tip that has a radius \begin{table}
\begin{tabular}{c c} \hline \hline
**Cut-Off \(\lambda\)\(c\) (mm)** & **Cut-Off \(\lambda\)s (\(\mu\)m)** \\ \hline
0.08 & 0.4 \\
0.25 & 1.25 \\
0.8 & 4 \\
2.5 & 12.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Setting the cut-off parameter \(\lambda\)s (ISO 3274, ISO 11562); [35,40]. ISO standards are used to report the nominal values of roughness standards. Figure 8: Percentage expression of the variability of the evaluated data \(Ra\) if the measurements were carried out for the given standard [33; 34; 35; 36; 37; 38; 39; 40; 51; 52; 53; 54; 55; 56; 57; 58; 59; 60; 61; 62; 63; 64; 65] at all possible speeds of the sensor movement. Figure 9: Percentage expression of the variability of the evaluated data \(Ra\), if the measurements were carried out for specific sensor movement speeds and only the evaluation norm, was changed during the experiments. of 2 \(\upmu\)m and an angle of 60\({}^{\circ}\) and is pressed with a measuring force of 0.75 mN (Table 3). Some types of surface testers allow you to select only the \(Lc\) parameter, and the second parameter of the cut-off filter is automatically set. However, there are also surface testers that allow you to independently set both parameters of the cut-off filter, so the mentioned standards provide a recommendation in the form of a table (Table 3) for choosing these settings. In some cases, the surface tester also allows the replacement of the stylus and thereby changing its geometry, where the standards bring certain recommendations. Similarly, the newer standard ISO 21920-3 [47] introduces default settings for functional parameters (_Rk_, _Rpk_, _Rpk_, etc.) and R- and W- parameters without defined defaults (Table 4). The so-called setting class, while the difference is only in the values of the parameter \(\lambda s\). The problem is that if we determine the \(Ra\) of the assessed surface, we choose L-filter \(Lc\). If, for example, we choose a too-small value of L-filter \(Lc\) for the sample, then the result is \(Ra\) with an almost zero size. However, if we choose a value of \(Lc\) that is too large, then the value of \(Ra\) may also include the effect of waviness and will distort the value of \(Ra\). The mistakes we make when choosing a bad cut-off can be huge and can have a fatal impact on the result of evaluating the roughness of the surface of the component under consideration. We will try to solve this problem in this work. For the practical measurement of surface roughness parameter values, it is important to choose the L-filter \(Lc\) (the cut-off value for the stylus-based surface roughness tester) in such a way that it includes a sufficient number of profile irregularities characterizing its roughness and at the same time excludes the influence of irregularities with a larger spacing (with longer wavelength) of inappropriate roughness (profile waviness and profile shape). For the comparability of the surface roughness measurement results, the values of the basic length \(Lc\) (cut-off) are determined by the standard. The nominal values of the limit lengths of the profile filter \(Lc\) (cut-off) are selected from the following series: 0.08 mm, 0.25 mm, 0.8 mm, 2.5 mm, and 8 mm.