A cutting tool mechanism for converting a rotary motion to an orbital, oscillatory or impact motion, said mechanism comprising: an inner circular part comprising teeth members, which extend radially outwardly; a surrounding circular part comprising teeth members, which extend radially inwardly; where said inner circular part teeth members are fewer in number than said surrounding circular part teeth members; where said inner circular part co-operates with said surrounding circular part by engagement of said inner circular part teeth members with said surrounding circular part teeth members; and where, as a one of said inner circular part and said surrounding circular part rotates about a central axis of an input coupling (81, 111) of the mechanism, an other of said inner circular part and said surrounding circular part is configured to move constrained by the engagement of said teeth members (19, 27) of said inner circular part and said surrounding circular part, wherein the engaging teeth members ride along and over each other to provide an orbital, oscillatory or impact motion in the other of said inner circular part and said surrounding circular part; wherein the input coupling (81, 111) is connected for transmission of rotary motion about the central axis to the one of said inner circular part and said surrounding circular part; and wherein the other of said inner circular part and said surrounding circular part has an output coupling configured to receive a blade, the output coupling configured to transmit said orbital, oscillatory or impact motion to the blade, to oscillate the blade between a maxima away from and a minima toward the central axis. an inner circular part comprising teeth members, which extend radially outwardly; a surrounding circular part comprising teeth members, which extend radially inwardly; where said inner circular part teeth members are fewer in number than said surrounding circular part teeth members; where said inner circular part co-operates with said surrounding circular part by engagement of said inner circular part teeth members with said surrounding circular part teeth members; and where, as a one of said inner circular part and said surrounding circular part rotates about a central axis of an input coupling (81, 111) of the mechanism, an other of said inner circular part and said surrounding circular part is configured to move constrained by the engagement of said teeth members (19, 27) of said inner circular part and said surrounding circular part, wherein the engaging teeth members ride along and over each other to provide an orbital, oscillatory or impact motion in the other of said inner circular part and said surrounding circular part; wherein the input coupling (81, 111) is connected for transmission of rotary motion about the central axis to the one of said inner circular part and said surrounding circular part; and wherein the other of said inner circular part and said surrounding circular part has an output coupling configured to receive a blade, the output coupling configured to transmit said orbital, oscillatory or impact motion to the blade, to oscillate the blade between a maxima away from and a minima toward the central axis.