Species-dependent effects of tool geometry and machining parameters on surface roughness during longitudinal up-milling of Mongolian Scots pine and white oak

Previous studies on wood milling have mainly examined individual species or restricted machining conditions, leaving uncertain whether responses to tool geometry and cutting parameters are transferable across anatomically contrasting woods. This study aimed to distinguish common from species-dependent parameter effects during longitudinal up-milling of Mongolian Scots pine (Pinus sylvestris var. mongholica Litv.) and white oak (Quercus spp.). The novelty lies in applying an identical four-factor, three-level full-factorial design to both species to compare the effects of rake angle (γ), helix angle (λ), milling depth (ap), and feed per tooth (fz). Surface roughness (Ra) was measured with a 2 μm stylus parallel to the wood grain and feed direction, representing direction-specific longitudinal profile roughness. fz was the dominant factor, accounting for 41.6% and 46.8% of Ra variation in pine and oak, respectively (p < 0.001). No two-factor interaction was significant for pine, whereas oak exhibited a significant γ×λ interaction (p = 0.004). Species-specific two-factor interaction models identified low-Ra parameter combinations and achieved validation errors of 4.21% and 18.34% for pine and oak, respectively. Overall, fz was the common primary factor controlling longitudinal Ra, whereas tool geometry optimisation was species specific.