Belt drive unit for a molding machine or bored fins, in particular for heat exchangers, with controlled adaptability to bores of different diameters

A drive unit of a belt for a molding machine for bored fins, for heat exchangers, comprising a fixed front part and a movable rear part driven longitudinally with a forward and backward movement to and from the fixed front part, wherein both parts of the drive unit include, on upper surfaces thereof, support plates for movable vertical teeth with oblique top which protrude upwards under elastic thrust and are suitable for being inserted into corresponding bored collars of the belt downstream of a boring unit of the molding machine, wherein the vertical teeth of a movable rear part drive the belt forward during the forward movement of the movable rear part and then lower below the plane of the belt to leave the belt in the position reached during a next backward movement of the movable rear part, while the vertical teeth of the fixed front part keep the belt in the position reached, which is suitable for a next cutting operation, during the step of moving the movable rear part backward, the improvement comprising that the upper surfaces of each of two movable and fixed parts of the drive unit support at least a further support plate for movable further vertical teeth with an oblique top of greater diameter, which are liftable and lowerable by a control panel and the vertical teeth of smaller diameter are replaced with the further vertical teeth.