## 4 Conclusions  
In the present study, a comprehensive study on the determination of the effect of a pure WJ treatment on the surface quality of pockets milled by AWJ technology was carried out. Different conditions were tested based on a different number of pure WJ passes and traverse feed rate values, and two different series of experiments were carried out depending on different roughing conditions. After the results were analyzed, several conclusions were drawn. The average surface roughness and maximum dimension of the profile cannot be effectively reduced by one or two pure WJ passes, especially under the same traverse feed rate as the roughing step. Although the average values of Ra and Rz vary in respect to both the number of passes and the traverse feed rate, their variation along the pocket surface is relatively high in most cases, indicating that a pure WJ treatment cannot be considered capable of improving the surface quality with a simple machining strategy. The analysis of Rp and Rv revealed that a plausible reason for the inefficiency of the pure WJ treatment was that the additional depth of pocket removed by the pure WJ was much lower than the size of the peaks, leading to only partial removal of the peaks and probable separation of the previously merged impact sites, thus maintaining or even increasing the average roughness of the surface, as well as the peak height. Moreover, the action of the waterjet in void regions between the impact sites can further increase the difference between the highest peaks and lowest valleys, thus increasing Rz. Waviness of the surface was the only quantity that was shown to be positively affected by the pure WJ treatment, as it could be decreased after subsequent pure WJ passes, especially in the second series of experiments. Thus, it can be deduced that a pure WJ treatment under the tested conditions is more favorable for higher-order surface deviations. The analysis of the Rsk-Rku topological map indicated that a pure WJ treatment on average increased the skewness and kurtosis of the surface so that a surface with dominant peaks occurred, probably increasing the friction coefficient and lowering the oil retention capability, something that was implied by the greater impact of a pure WJ treatment on the average Rp than the Rv values. Finally, the findings of this work can provide useful suggestions for the improvement of the efficiency of a pure WJ treatment. It is advised that further research on the use of different milling strategies, e.g., adopting multiple WJ passes, should be carried out in order to appropriately regulate the jet pressure and stepover apart from the traverse feed rate in order to remove a larger amount of material and effectively remove larger peaks without leading to further deterioration of the surface by plastic deformation. Thus, it is possible to use a pure WJ treatment as an eco-friendly and low-cost means of pocket finishing. Conceptualization, N.E.K. and P.K.-O. ; methodology, N.E.K. and P.K.-O. ; software, N.E.K. ; validation, N.E.K. ; formal analysis, N.E.K. ; investigation, N.E.K. ; resources, P.K.-O. ; data curation, N.E.K. ; writing--original draft preparation, N.E.K. and P.K.-O. ; writing--review and editing, N.E.K. ; visualization, N.E.K. ; supervision, N.E.K. and P.K.-O. ; project administration, N.E.K. and P.K.-O. ; funding acquisition, N.E.K. All authors have read and agreed to the published version of the manuscript. This research was supported by the Polish National Agency for Academic Exchange (NAWA, Agreement No. BPN/ULM/2022/1/00129/U/00001). Not applicable. Data Availability Statement: Data are contained within the article. The authors would like to sincerely thank [PERSON] regarding the determination of the diameter distribution of abrasive particles used in the present work. Conflicts of Interest: The authors declare no conflicts of interest.