A rotary cutting unit for trimming sheet material has a support plate for receiving the sheet material. The rotary cutting device having a guide bar with a displaceably guided knife carriage. A rotary knife is rotatably mounted on the knife carriage. The guide bar is guided between an initial raised position and a lowered clamping position. The guide bar includes a clamping surface for contact against sheet material. The guide bar has a force impinged upon it by a spring device, in the direction toward the initial position. An actuation device moves the guide bar out of the initial position into the clamping position. The guide bar is clamped in vertically movable fashion between the spring device and a further spring device. The second spring device has a spring action directed oppositely to the first.