Toward teaching a robot

In a plastic key joint wherein edge portions of two adjacent strakes are in relatively superposed, interfitted, edgewise engagement with each other in a manner to define a fully enclosed keyway therebetween, the present invention resides in deforming, preferably in an undulating or sine wave pattern, laterally opposite sides of the keyway prior to injecting, under selected pressure, flowable, hardenable key material into the keyway, thereby greatly increasing resistance of the joint to longitudinal shear stresses.