This is a perennial question from new lathe owners. With the motor running, and the FWD-REV gearbox in FWD or REV (Atlas 9" or 10" without QCGB) or the Tumbler lever in either FWD or REV (all other Atlas or Atlas-Craftsman models), the lead screw should be turning. If the carriage is stopped with the half nuts (AKA split nuts) open/disengaged and the gear on the bottom of the threading dial engaged/meshed with the lead screw, the threading dial should be turning. This is normal. When you engage or close the half nuts, the carriage should start to move to the left or the right. And the threading dial should stop rotating. THIS IS ALSO NORMAL! The reason is that with the carriage moving to the left or right as the lead screw turns, it and the threading dial gear are not moving relative to the top of the lead screw thread visible just to the right of the threading dial. So the threading dial gear and dial do not rotate.