Large flange reference circle line drawing device

A large flange reference circle line drawing device comprises a supporting plate, a lock screw, a paintbrush ruler and a scriber. The large flange reference circle line drawing device is characterized in that a horizontal through hole is formed in the middle of the supporting plate, the paintbrush ruler is inserted in the horizontal through hole and fixed by the lock screw, and the scriber is arranged at the end of the paintbrush ruler; the portions, which are located on the two sides of the horizontal through hole, of the supporting plate are symmetrically provided with front screw holes and back screw holes which are in the vertical direction, sliding bolts are connected with the back screw holes in a threaded mode, the bottom ends of the sliding bolts are provided with ball bearings, sleeve bolts are inserted in the front screw holes, steel balls and springs are placed in inner cavities of the sleeve bolts, and compression bolts are connected with the inner cavities of the sleeve bolts in a threaded mode. The large flange reference circle line drawing device is skillful in design, simple in structure and convenient to use, and capable of drawing a needed reference circle on a large flange; the production cost is far lower than that of an existing large compass.