# The Difficulty of Measuring the Roughness of Glossy Surfaces Using the Triangulation Principle
## 3 Results  
Due to the characteristics of glossy surfaces, measuring their roughness using contact-free laser profilometry can be challenging. The samples were made using laser-cutting technology. The roughness parameters values measured using the laser profilometry were then compared with the roughness parameters values measured with the Surftest SJ-400 contact roughness meter. The graphical representation of the Ra parameter (Figure 10) illustrates the average surface roughness at different measurement lines (1, 2, 3) and parts of samples A, B, and C (length of the measuring section) for stainless steel and aluminum alloy, measured using contact-free and contact methods. These results were consistent with the conclusions reached by [PERSON] et al. [21], [PERSON] et al. [28], and [PERSON] et al. [29]. \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameters** & **Value** \\ \hline Measuring speed (mm \(\times\) s\({}^{-1}\)) & 0.05; 0.1; 0.5; 1.0 \\ Speed of return (mm \(\times\) s\({}^{-1}\)) & 0.5; 1.0; 2.0 \\ Positioning & \(\pm\)1.5\({}^{\circ}\) (inclination); 10 mm (up/down) \\ Measurement range/resolution & P (primary); R (roughness); W (filtered waviness) \\ Evaluated parameters & 0.889 \\ Digital filter & 2 CR; PC75; Gauss \\ Cutoff length (mm) & 0.08; 0.25; 1.8; 2.5; 8 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Individual parameters of the Surftest SJ-400 roughness meter. Figure 9: Samples with designated measurement lines and transverse zones. A comparison of the graphed dependencies involving the Ra parameter, which was measured in individual samples in a contact-free and contact manner, shows an obvious difference if we do not take into account the material used for the production of the samples (Figure 10). The measured Ra parameter values in the A304 material using the contact-free laser profilometer ranged from 12 to 18 \(\upmu\)m, while the reference values measured with the contact roughness meter ranged from 1.6 to 2.5 \(\upmu\)m. Similarly, the measured Ra parameter values in the AW 2017 material using the contact-free laser profilometer ranged from 8 to 13 \(\upmu\)m, while the reference values ranged from 5.7 to 6.7 \(\upmu\)m. This difference between the values measured with the contact-free method and the reference values are caused by the unwanted glare of the camera sensor, which leads to measurement error. However, this error can be partially eliminated by deleting the outlier values from the exported tables. These conclusions are supported by the findings of [PERSON] et al. (2017) and [PERSON] et al. (2017). The 3D model shown in Figure 11 was generated by combining multiple profiles measured by the laser profilometer using the laser profilometry View software. In the image, the blue arrow indicates areas on the sample where the laser light reflected most strongly onto the CMOS camera. The software interpreted these areas as having the greatest surface roughness and reported them as sharp increases in the Ra parameter values. There is also a visible difference in the Ra parameter in the materials of the samples used that were produced by laser technology of material cutting. In the contact method, the value of the roughness parameter Ra of the AW 2017 aluminum alloy material is in the order of 4 \(\upmu\)m greater than that of the stainless steel material sample. In general, we can conclude that the stainless steel used is significantly harder than the aluminum alloy,  
Figure 11: 3D model of the scanned sample made of AW 2017 (section A, 5 \(\times\) 22 mm). _X_-axis—red line; _Y_-axis—yellow line; _Z_-axis—blue line. Figure 10: Graphed dependence of the average Ra values on the length of the measurement lines (1, 2, 3) and section (A, B, C) for stainless steel A304 and aluminum alloy AW 2017.  
which means that the roughness we achieve on the surfaces cut by laser-cutting technology is better for harder materials. In the contact-free method, the measured values of the roughness parameter Ra are higher for a sample made from stainless steel than from the aluminum alloy.