Statistical Lower Tolerance Limits for Rectangular Mortise and Tenon Joints

Abstract

Tests were conducted to determine the bending moment capacity of 215 red oak and 140 white oak T-shaped rectangular mortise and tenon joints. Rails measured 22.2 mm by 63.5 mm in cross section; tenons measured 32 mm in length by 38 mm in height by 9.5 mm in thickness. Specimens were assembled with a 40% solid content polyvinyl acetate adhesive. The average bending moment capacity of the red oak specimens was 353 Nm with a standard deviation of 48 Nm; in the white oak specimens, it was 358 Nm with a standard deviation of 62 Nm. The lower tolerance limits of the red oak specimens at the 75|75, 90|75, 75|90, 90|90, and 95|95 confidence|proportion levels were 318, 316, 289, 286, and 266 Nm, respectively, whereas in white oak specimens, the values were 314, 308, 273, 268, and 240 Nm, respectively. Overall, the results indicated that the use of statistical lower tolerance limits procedures provide a systematic means of relating standard deviations to mean values in determining reasonable design values for the moment capacity of the joints. Conclusions were not reached concerning which confidence|proportion level might be best suited for determining reasonable design values for furniture joints, but the results did illustrate the consequences of a given choice.