A jump arm assembly for a tilling machine includes a jump arm and a disc hub assembly for coupling a tilling disc to the jump arm. The jump arm has a first end configured to be coupled to a frame unit of the tilling machine and a second end opposite the first end. The disc hub assembly includes a hub housing and a shaft having a first axial shaft section and a second axial shaft section. The first axial shaft section is configured to be rotatably mounted within the hub housing. The second axial shaft section extends outwardly from the hub housing and is at least partially threaded to receive a threaded nut to secure the tilling disc to the disc hub assembly.