A system and method of making up and breaking out a dual-member drill string. The system comprises a spindle, a spindle carriage and a drive frame. The drive frame provides thrust to the spindle, while the spindle carriage provides rotation. The spindle has an outer spindle and an inner spindle, and is adapted to connect to a pipe section having an outer pipe section and an inner pipe section. Inner joints are geometrically shaped, while outer joints are threaded. When making up dual member drill string, the spindle is advanced, with the outer spindle rotating, and the inner spindle rotating in alternating directions, or “dithering.” A float sensor and a processor are used in tandem to cooperatively couple the inner spindle with the inner pipe sections and the outer spindle with the outer pipe sections.