A drawing system has software (SW) providing tools to enable a user to create geometric objects in a display, and to select and drag the objects in the display. An assembly engine is a part of the SW, and monitors properties of objects and movement of objects in the display. The assembly engine monitors features and properties of a first object selected and dragged, and features and properties of second objects in the display, determines compatible geometric features that might be joined in assembly between the first and second objects, and upon compatible features for join being moved within a preprogrammed threshold distance (TD) in the display, affects a join operation, bringing the compatible features of the first and the second object together in an assembly and redrawing the assembly.