Described is a mechanical transmission (T) comprising a containment structure (1) housing a roto-translational element (2), extending along an axis of rotation (X) and comprising a first and a second threaded portion (3, 4), a rotary element (5) connected or connectable to a drive unit to define a mechanical power input unit and equipped with a first thread (8) designed to engage rotatably with the first threaded portion (3) to the roto-translational element in such a way as to define a first threaded connection, a fixed guide (9) having a second thread (14) designed to engage with the second threaded portion (4) of the roto-translational element (2) in such a way as to define a second threaded connection, and a translating element (10), translating along the axis (X) and defining a power output unit. The translating element (10) is connected to the roto-translational element (2) for translating at the same linear speed as the roto-translational element (2). The roto-translational element (2) is thus simultaneously coupled to the rotary element (5) and to the fixed guide (9) respectively by means of the first and second threaded connections. These connections have different pitches in such a way as to vary the angular speed between the roto-translational element (2) and the rotary element (5).