Coffee making machine

An infusion group for a machine for preparing infusions from a compressed powdered substance, the group comprising a moving member (2) having a longitudinal internal cavity (3) open at its ends and adapted to receive a dose of said powdered substance fed through means (16, 17) for introducing the powdered substance, and means (8, 9, 18, 19) for causing an axial translation of said member (2) relative to a pair of confronting pistons (4, 5 ), one of which is a moving piston (4) connected to said translation means (8, 9, 18, 19) so as to be axially translated, and the other one is a stationary piston (5), said pistons (4, 5) being adapted to co-operate with said cavity (3) by tightly engaging the cavity walls in order to define an infusion chamber and having heads (23, 27) equipped with filters (25, 28) between which said dose of powdered substance can be compressed because of the translation movements of said moving member (2) and said moving piston (4), characterised in that said translation means (8, 9, 18, 19) comprise a first and a second threaded shaft (8, 9) that are associated with said moving member (2) and said moving piston (4), respectively, and are simultaneously rotated in opposite directions by a driving member so as to cause simultaneous axial translation, in opposite directions, of the moving member (2) and the moving piston (4).