A computer-based system and method generate a movement of a 3D part of a 3D assembly in a 3D scene. Movement of the 3D part represents rotation by a predetermined angle. The method a) displays a 3D assembly of 3D parts in the 3D scene; b) selects a 3D part of the 3D assembly; and c) displays in the 3D scene a 3D manipulator. The 3D manipulator comprises three axes, and is anchored to the 3D part at an anchor point. The method then d) drags the 3D manipulator along one axis by a current distance from the anchor point on the axis. The predetermined angle corresponds to a maximum distance from the anchor point. The method e) while dragging the 3D manipulator, computes a ratio of the current distance to the maximum distance, and f) generates the movement of the 3D part proportionally to the ratio.