Bending moment capacity of round mortise and tenon furniture joints

Tests were conducted to determine the effect of cross pinning the tenons of round mortise and tenon joints on the bending moment capacity of the joints. Tenon diameters ranged from a nominal 0.6 to 1.0 inches. Cross-pins were about one-half the diameter of the tenons. Both wood and steel cross-pins were included. Cross pinning was found to reduce the bending moment capacity of red oak joints by 33 percent and the capacity of yellow-poplar joints by 38 percent. Smaller cross-pins had less effect than larger cross-pins, and offsetting the pins toward the tip of the tenon also caused less reduction in bending moment capacity. Results also tend to indicate that the form factor for round beams, i.e., 1.18, should be incorporated into the flexure formula when estimating the bending moment capacity of round tenons. Finally, the results indicate that the shoulders on tenons significantly increase the bending moment capacity of a joint when the shoulders of the tenon fit firmly against the side of the member in which the tenon is inserted