A device for cutting glass for example separating a drop or portion of a plastic glass skein emerging from a feeder characterized by having two shear arms mounted for rotation in a common frame, each of the shear arms being provided with a knife at its extreme end and a device for periodically moving the arms in a pincher-like closing movement toward one another and away from one another so that the knives can execute a cutting process. The device for periodically moving includes a device for forming a periodic working cycle preferably comprising at least one cam having one segment forming a working stage of a working cycle and a second segment forming an idle stage. By varying the speed of rotation of the cam while the follower is in the second stage, a time delay between the closing of the knives can be adjusted without changing the speed of movement during a cutting stage.