## 2 Materials and Methods  
A schematic representation of a novel processing of wooden workpieces by roller pressing is provided in Figure 1. The workpiece, passing between two rotating rollers, is under the action of pressing force \(F\). The force acts on surface \(A\), whose size depends upon the rollers' diameter \(R\). To achieve the identical depth of the deformed layer on both sides of the wood sample, the diameters of the rollers must be identical. The roller penetration depth \(h\) depends not only on the force and the size of surface \(A\). It is also affected by angular velocity \(\omega\), which defines the holding time of load in a particular zone of the workpiece. Furthermore, due to the inhomogeneous structure of wood, the roller penetration depth is affected by the inhomogeneity of the material in the processing zone. Elastic deformation (elastic recovery) of the material, \(\Delta a_{e}\), which occurs after the processing, and its influence on the final dimension (thickness) \(a_{f}\) of the processed workpiece, must be considered as well. Figure 1: Schematic representation of roller pressing process. Roller pressing is conducted on a specially developed device shown in Figure 2. The base plate (1) and vertical plates (2) are interconnected by bolts, forming a framed structure. The device is resting on horizontal support and levelled by the adjusting screws, which is important for the correct realisation of the normal force, i.e., the force of rollers' penetration into the material. Fixed to the base plate via carrier (4), a stepper motor (5) is connected by a belt drive (6) to the lower, i.e., drive roller (7), which has only one degree of freedom--rotation about its central axis. The angular velocity of the drive roller is regulated by the control unit of the stepper motor. All tests were performed at an auxiliary speed of 250 mm/s. A workpiece (8) is placed between the lower, i.e., drive roller (7) and the upper, driven roller (9). The diameters of both rollers are 50 mm. On a shaft (10) passing through the upper roller, weights (11) are placed to achieve the pressing force. The construction solution enables translational motion of the upper roller, shaft, and weights along the groove on the vertical plate (2). The processing is performed at a constant force of rollers' penetration into the workpiece. The force is achieved by placing weights of identical mass left and right of the workpiece axis at equal distances. The Seeger rings (12) placed in the grooves on the shaft secure the weights' position on both sides. The limiters (13) prevent the workpiece movement in the axial direction of rollers. Effects of the described roller pressing method were investigated on eight different types of wood: oak, beech, ash, walnut, fir, cherry, linden, and alder (Figure 3). All samples were with identical cross-sections of 40 \(\times\) 10 mm. To achieve uniform test conditions, samples were prepared taking into consideration the fibre orientation. Testing of each type of wood was conducted on thirty samples to make the influence of factors such as material inhomogeneity or wood moisture negligible. Figure 2: Device for the processing of wood samples by roller pressing. Before and after the roller pressing treatment, the hardness and roughness of the processed surface were measured and the mean values of the elastic modulus of samples were determined. The processing of wood blanks was performed by applying the following values of pressing force: 392 N, 785 N, 1177 N, and 1570 N. To achieve greater deformation of the surface layer, the processing was carried out in four passes. Measurements were repeated thirty times. The hardness was measured according to the EN 1534 standard. A thin layer of black paint was applied to the indenter before each indentation to leave a visible trace, considering the weak reflection of the wood surface. The use of paint allows accurate reading of the results, reducing the error in measurement of the indentation diameter, especially in the direction of fibres.