Machine for stretching films or sheets

Machine for stretching films, comprising two tracks each having a first rail (1) on which clips (3) move and close together at a point for adjusting their pitch and a second rail (2) on which carriages (5) each having a roller move, wherein that the carriages are articulated, in a chain driven in a direction of movement by a toothed drive wheel (6) driven at a peripherical speed, with two consecutive clips (3) respectively, the machine having a mechanism for indexing the a pitch adjusting point of the clips (3), wherein the indexing mechanism is formed on the one hand by a toothed indexing wheel (8), arranged downstream in the direction of movement of the chain and driven at the same peripheral speed as the drive wheel (6), and on the other hand by a roller (5) of the carriage entering into the tooth gap of the indexing wheel (8) when the clip, further downstream in the direction of movement of the chain and corresponding to said carriage, is at the point for adjusting the pitch of the clips.