In one example, a 3D printing system includes a support structure generator to identify a breakaway support to temporarily support part of the object, to design a wedge shaped groove between a portion of the object and the support, the groove ending at a line along which the support intersects the object, and to generate a digital object model that includes the support and the groove. The system also includes a 3D printer to print the object, support and groove based on the object model.