Characterizing Roughness of Wooden Mortise and Tenon Considering Effects of Measured Position and Assembly Condition

The surface roughness of wood mortise and tenon seriously influence the strength of mortise-and-tenon joints. However, it is difficult to obtain the whole surface roughness of mortise and tenon due to the limitation in measuring range of most profilometers. Therefore, the selection of measured position is critical to measuring the roughness of mortise and tenon. This study mainly aimed to investigate the effects of measured position in the thickness direction (T1, T2, and T3) and length direction (L1, L2, and L3), and assembly condition (unassembled and assembled) on the surface roughness of wood mortise and tenon to characterize their surface roughness. Roughness profile results showed that the average roughness of mortise (4.53 µm) was greater than that of tenon (3.89 µm), and the roughness of unassembled ones was greater than that of assembled ones. The roughness at all measured positions of unassembled mortise was nearly identical, while for unassembled tenon, roughness in the thickness direction varied. T2 was significantly greater than those of T1 and T3. Statistical analysis results showed that for an unassembled sample, sample type and measured position in the thickness direction significantly influenced roughness, but measured position in the length direction was not significant. Assembly condition significantly influenced the roughness of tenon; the roughness of assembled tenon decreased significantly compared with unassembled tenon. The roughness at T2L1 decreased so much compared with T2L2 and T2L3. It can be concluded that the roughness of mortise was mainly dominated by its grain orientation of the measured surface, which was perpendicular to the grain. The roughness of unassembled tenon varied and resulted from the tangential feeding speed of the machine changing during the manufacturing of the curved part of the tenon. The cutting speed at T2 of wood tenon was faster than those of T1 and T3, so the roughness at T2 was greater than those of T1 and T3.