## 4 Summary and Conclusions  
We achieved our objectives defined in the beginning of this work. We determined the dimensional deviations of the thin walls in the horizontal orientation for manufactured Inconel 625 nickel alloy samples, machined with a combination of three cutting tools and two machining strategies. We obtained results for both perpendicular and parallel directions with respect to the feed motion. We measured the deviations using a 3D optical scanner (optical method) and a coordinate measuring machine (contact method). The present results might be considered in conjunction with those in other papers from our international team [1; 29]. Thus, we provide some further conclusions:  
* The use of the tool for general purpose with an adaptive face milling strategy (N1) resulted in lower deviations compared to a combination of the same tool, however, with the opposite strategy--adaptive cylindrical milling (N4). For the other tools, i.e., the tool for high-performance machining and the tool for high-speed machining, lower deviations were recorded during using adaptive cylindrical milling (N5 and N6) compared to face milling (N2 and N3). * The lowest deviation value was characterized by specimen N1 (maximum deviation: 0.28 mm), which was made with the tool for general purpose using adaptive face milling, while the highest deviation was found in specimen N3 (maximum deviation: 0.58 mm), made with the same strategy but using the tool for high-speed machining. * Thin wall thickness close to the assumed value of 1 mm was obtained for all samples except N5, for which the value was about 0.9 mm. * For two specimens (N3--the tool for high-speed machining using adaptive face milling; N4--the tool for general purpose using adaptive cylindrical milling), the stability of taken deviation values was observed at individual measurement points. * For samples N1, N2 (adaptive face milling), and N5 (adaptive cylindrical milling), an increase in deviation values was observed until the face of the tool was fully engaged (up to about 10 mm). This is an effect of the stiffness of the tool-spindle system, which, in these cases, was due to the lack of constraining the mill with material on the underside, which slightly reduced the emerging tool deflection at the initial stage of milling. * During the application of adaptive cylindrical milling, a characteristic shining appeared in the last passes, which caused a decrease in the deviation values. A comparison of the deviation results obtained from the contact and optical method measurements revealed similarity in the distribution of graphs in selected sections. We obtained the maximum discrepancy of the results equal to 8%--as in the case of the previous study [1]. This result confirms that a 3D optical scanner can be used when measuring thin-walled structures of small dimensions with relatively good measurement accuracy. Further research could focus on checking other machining parameters that would enable products with smaller dimensional deviations, as well as checking other ways of clamping the sample that would minimize vibration and, consequently, deformation of the thin walls. As noted in the beginning, the use of thin-walled structures is increasing in several industries--including the aerospace industry. Consider, now, instruction in materials science and engineering (MSE). Teaching MSE typically includes ceramic materials and biomaterials [38], geopolymers [39], polymer classes such as epoxies [40], wood [41], wastewater recycling [42], or specific properties such as fire resistance [43]. Coverage of thin-walled structures in MSE instruction seems worthwhile. Conceptualization, S.K. ; methodology, S.K. and K.Z. ; software, S.K. ; validation, K.Z., J.C. and K.S. ; formal analysis, S.K. ; investigation, S.K. ; writing--original draft preparation, S.K., J.C. and W.B. ; writing--review and editing, S.K., K.Z., J.C., K.S. and W.B. ; visualization, S.K. ; supervision, J.C. and K.S. ; project administration, S.K. and K.S. ; funding acquisition, S.K., J.C. and K.S.