A metering machine for the formation and deposition of volumetrically predetermined quantities of a fluid or semi-fluid substance configured as (C) drops (GC) on a substrate (PB) in relative movement with respect to the metering machine, comprising: a support structure (4), a metering unit (8), associated with the support structure (4), comprising a chamber (10) containing the substance (C) to be metered, communicating with at least one metering duct (14) provided at its end opposite the chamber (10) with a delivery nozzle (22), valve means (26) interposed between the metering duct (14) and the nozzle (22) which, in their normally closed position, prevent the substance (C) from flowing from the duct (14) to the nozzle (22), at least one piston (16) sliding in a leak-tight manner in the metering duct (14) and moving in an alternating manner between a retracted position, in which the substance (C) to be metered is able to flow from the chamber (10) to the metering duct (14), and a forward, end-of-stroke position within the metering duct (14), the displacement of the piston (16) between the retracted position and the forward position causing the valve means (26) to open and the metered quantity of substance (C) contained in the metering duct (14) to be expelled via the nozzle (22), and actuator means (6) borne by the support structure (4) in order to cause the alternating movement of the piston (16) within the metering duct (14), the actuator means (6) being adapted to provide the piston (16), in its stroke from the retracted position to the forward position, with a high kinetic energy such as to cause the expulsion of the substance (C) to be metered with a projectile flow.
