The present disclosure relates to methods and apparatuses for imparting a first line of weakness and a second line of weakness into one or more layers of an advancing substrate, such as a belt assembly. The first line of weakness is coincident with the second line of weakness. The advancing substrate may be a belt assembly including an outer layer, an inner layer, and one or more elastic strands disposed between the outer layer and the inner layer. A first surface of the belt assembly may be acted on by a first laser beam that operatively engages a first scan head and a second surface of the belt assembly may be acted on by a second laser beam that operatively engages a second scan head. A trim removal member may be used to separate the first and second lines of weakness forming a trim portion and a separation edge.