Abstract: Apparatus for forming incisions in a timber plank, comprises: at least two rotary incisors each comprising a plurality of circumferentially distributed teeth and arranged in use to rotate at the same rate to form respective patterns of incisions in a common face of a plank as it is moved past the incisors, said patterns having a predetermined longitudinal alignment between them; depth-controlling means arranged to maintain, for each incisor, a predetermined depth of penetration of the teeth thereof into the plank; means for adjusting said predetermined depths of penetration; and means for allowing adjustment of the incisors (double-arrow) to compensate for the altered spatial period in said patterns when the depths of penetration of the incisors are adjusted, thereby allowing said longitudinal alignment between the respective patterns to be maintained.