Abstract: A dado joint is provided between first and second members and includes at least one elongated groove formed in the first member of a constant width and constantly varying depth in the likeness of a shallow, smoothly curving sine wave. The second member includes a marginal edge tongue of constant thickness for mating with and snug reception within the groove, the tongue including a sine wave likeness longitudinal contour corresponding to the aforementioned sine wave and being seated and secured in the groove.