The objective of this study was to understand better the cutting forces and chip formation of Scots pine (Pinus sylvestris L.) with different moisture contents (MCs) and machined in different cutting directions. To that end, an orthogonal cutting experiment was designed, in which Scots pine was intermittently machined using a tungsten carbide tool to produce chips. The cutting forces were measured and the chip shapes were quantitatively described. Four conclusions can be drawn: (1) with increasing MC, the average cutting forces initially decreased and then stabilized, while the angle between the direction of the main and the resultant force continuously decreased. (2) The average cutting forces in the 90°–0° cutting direction were lower than the same forces in the 90°–90° cutting direction. (3) During machining, the dynamic cutting forces fluctuated less in the 90°–0° case. However, the dynamic feeding forces showed a decreasing trend in both the 90°–0° and the 90°–90° cases. (4) The process applied produced granule chips and flow chips, while less curly flow chips with a higher radius of curvature were more easily produced from samples with high MCs in the 90°–0° cutting direction.

This paper investigated the machinability of a stone–plastic composite (SPC) via orthogonal cutting with diamond cutters. The objective was to determine the effect of cutting depth on its machinability, including cutting forces, heat, chip formation, and cutting quality. Increased cutting depth promoted an increase in both frictional and normal forces, and also had a strong influence on the change in normal force. The cutting temperatures of chips and tool edges showed an increasing trend as cutting depth increased. However, the cutting heat was primarily absorbed by chips, with the balance accumulating in the cutting edge. During chip formation, the highest von Mises strain was mainly found in SPC ahead of the cutting edge, and the SPC to be removed partially passed its elastic limit, eventually forming chips with different shapes. Furthermore, the average surface roughness and the mean peak-to-valley height of machined surfaces all positively correlated to an increase in cutting depth. Finally, with an increase in cutting depth, the chip shape changed from tubular, to ribbon, to arc, to segmental, and finally, to helical chips. This evolution in chip shape reduced the fluctuation in cutting force, improving cutting stability and cutting quality.

To investigate the impact of different milling parameters on milling forces, chip morphology, and machined surface quality during the Paulownia milling process, we conducted experiments using cemented carbide single-tooth shank milling cutters. Additionally, we established a response surface model (RSM) to analyze milling surface quality. The key findings are as follows: milling forces along the parallel and tangential axes decrease with an increased tool rake angle and spindle’s rotational frequency, but they exhibit a positive correlation with milling depth. The effect of spindle’s rotational frequency on the milling force along the lateral axis differs due to the complex fiber characteristics of Paulownia. As milling depth decreases, chip morphology transitions from a block structure to a sheet structure, eventually becoming fragmented with shallow milling. Higher spindle’s rotational frequency and tool rake angle lead to a more fragmented direction in Paulownia chip morphology, while machined surface quality improves. Notably, under specific conditions, a striped chip morphology significantly enhances machined surface quality compared to similar milling parameters. The established RSM for machined Paulownia surface roughness is reliable and holds reference value for inhibiting surface damage in Paulownia machining.