Investigation of the effect of tool wear and wood species on surface quality and performance of finger-joint

Finger-jointed (FJ) lamellas are widely used in mass timber where bonding performance is critical for structural reliability. However, tool wear during FJ can affect wood surface characteristics, potentially affecting adhesive behavior and joint strength. In this study, Coastal Douglas-fir (DF), Hem-Fir (HF), and Western Redcedar (WRC) were machined using freshly sharpened and worn cutting tools and bonded with a polyurethane (PUR) adhesive to evaluate changes in surface topography, surface energy, adhesive wetting, ultimate tensile strength (UTS), and initial friction properties. The findings indicate that worn tool increased surface roughness (SA, SP, SV) for all wood species, which improved initial friction strength (IF-UTS) and coefficient of friction (IF-CoF), enhancing pre-cured joint integrity and stability. For DF, tool wear also increased UTS due to improved mechanical interlocking and adhesive penetration. In contrast, HF and WRC showed decreased UTS under worn tool conditions, despite increased roughness, IF-UTS, and IF-CoF, primarily due to reduced adhesive wettability and penetration. Glueline delamination remained low and was not significantly affected by wood species or tool wear, demonstrating the effectiveness of the PUR adhesive in accommodating surface variability. Overall, all FJ lamellas exceeded industry standards for UTS and failure modes, confirming reliable bonding performance. This study highlights the importance of balancing tool wear and wood species selection in FJ manufacturing. Moderate tool wear may be beneficial for DF, while maintaining sharp tools appears critical for HF and WRC. The findings provide valuable insights for optimizing machining strategies and improving the quality and consistency of structural FJ products in the wood industry.