**3. Discussion**

The experimental investigation of cuts made in very hard and wear-resistant steel concludes that relationships between the declination angle and roughness parameters are linear. The studied problem is close to the tailback and the taper investigations performed in the past by Hashish [16] or Ma and Deam [28]. Precise experiments studying surface quality on the selected process parameters of the Hardox steel plates cutting were revealing the traverse speed as the most important parameter influencing the accuracy of AWJ cutting were performed previously [11–13].

Calculation of the tilting of the cutting head for compensation of the declination angle effect on cut walls, presented, e.g., by a group of Ostrava researchers [17,29,30], should help to improve the cutting process and to minimize the typical defects caused by the abrasive water jet declination when the cut starts, ends, changes direction in the corners and in the curved parts of trajectories. Because according to the up-to-date results, no simple and direct relationship has been proved between common material properties and cutting quality for all types of cut material, the presented relations seem to be quite important. Their further investigation and confirmation for a broad spectrum of materials are necessary.

Models proposed in the present article may be evaluated from some points of view as simple; lacking physical linking of the parameters; but still in accordance with the main features of the more complex Hlavác model and with the experimental findings of other teams studying the quality of this ˇ type of cut materials and confirmed by experiments reported in Table 6. Thus, it may complement the variety of the materials and range of studied parameters and widen existing models for application in particular conditions.

The relations for these quantities should be the aim of further research because the miniaturization of abrasive water jets needs a strong and stable description to predict and control the production quality. Therefore, studying the surface topography on the cut walls is still important. Experimental and theoretical studies of the interaction problems are important for lifting the abrasive water jet tool to a higher level of operational excellence.
