## 1 Introduction
[44] presented an artificial neural networks (ANN) model, which proved to be very useful for modelling the characteristics of wood surface roughness without conducting additional experiments, thus saving time and reducing the high costs of experimental investigations. Furthermore, to obtain higher surface quality, they suggested specific parameters of finishing tools and a high grit number of the abrasive for particular types of wood. To obtain lower values of surface roughness, a suitable method for the adjustment of process parameters is Taguchi [45]. The results of Taguchi analysis indicate that the variable that most significantly affects the surface roughness is the grit number of the abrasive. Burnishing is a no-chip process in which the force applied to the material causes plastic deformation of a surface layer. During the burnishing process, a roller or a ball pushes surface materials from the peaks into the valleys, flattening the asperities, thus improving surface integrity, i.e., surface finish and hardness of a workpiece. This cold forming operation occurs on a small scale in which strain hardening enhances the surface hardness and strength, providing a mirror-like surface finish and compressive residual stress in the surface and subsurface layers resulting in better fatigue life [46; 47]. The authors of this paper previously investigated how ball burnishing improves the mechanical properties of wood samples. Ball burnishing has a positive effect on surface roughness and can increase the hardness of surface layers of treated materials up to three times [48]. The treated samples have better water absorption resistance, of even more than 60%, depending on the type of wood [49]. The roller burnishing process requires less time than other finishing techniques. In addition, it achieves the best circularity of the holes, the highest microhardness, a more uniform structure of treated surfaces, an optimal combination of surface characteristics and mechanical properties, increased abrasion resistance of the finished surface, and the absence of notches. Finally, it is an environment-friendly process [50]. [PERSON] et al. [51] wrote about the burnishing of wooden shafts in which the load, heat, and friction between the tool and the machined surface act simultaneously, improving the condition of the surface layer. Experiments were conducted on a lathe with a slide diamond burnisher and active (loading) forces of 30 N, 50 N, and 70 N. The treated elements were made of great map (_Acer pseudoplatanus_ L.). An arithmetical mean height of 2.85 um was obtained with a relatively small dispersion of the results. Critical limiting factors during the investigation were the heterogeneous structure of the wood and the load force. During the burnishing process, an excessive increase in force applied to improve the hardness of wood can cause significant damage to the processed surface. On the other hand, densification of the surface layer of lumber by the use of this method reduces the consumption of varnishes and paints during the final processing of products such as balusters and mouldings. In certain wood processing methods, the applied pressure has significantly higher values than in the roller pressing process. In briquetting, high pressure is used to remove the air from the intermolecular space and cause the gradual densification of the material [52]. In previous research, wood processing was investigated from various aspects because the surface quality, hardness, and other factors related to the specific wood structure significantly affect the results. To achieve the most reliable and accurate values of wood characteristics, researchers continue to modify and improve standard measurement methods, using various statistical methods and process modelling based on artificial intelligence. Enhancement of wood characteristics by increasing the density of layers beneath the surface is accompanied by the improvement of chemical processing methods, heat treatment, and thermo-hydro-mechanical treatment of wood.