Effects of end-pressure on the finger-joint quality of black spruce lumber: A microscopic analysis

Efficiency of finger-joints in the Engineered Wood Products is key to the performance of these products. The aim of this research work was to evaluate, by scanning microscopic analysis, the effect of end pressure on the performance of horizontal finger-joint of black spruce (Picea mariana (Mill.) B.S.P) specimens. A feather joint configuration glued with an isocyanate type of adhesive cured at room-temperature was used. The finger-joints were machined at a feed rate of 18.3 m/min, rotational speed of 3500 rpm, and at a feed per knife (chip-load) of 0.86 mm. A single-face glueline application was used at a spread rate of 110 g/m2. The curing time was kept at 24 hours. Six end-pressure levels ranging from 1.38 MPa to 4.82 MPa applied for 20 seconds were investigated. Results showed that cell depth damage increased as end-pressure increased. Joints also showed formation of some air bubbles within the glueline which lead to a reduction in their tensile strength