Sorry for posting so late on this issue. I have been reading through these posts and I agree that the motor is probably wired for Wye (Star) Connection. This connection puts a lower voltage on each of the three windings, so each winding sees about 57% of the voltage it would see if connected Delta. Interestingly, the motor will run at or near full speed assuming the loads on the motor are low enough, meaning the belts are not too tight and not so much friction. This Wye connection is often used as a means of starting a motor and getting it up to full speed before reconnecting the windings as a delta connection (done through a sequence of mechanical switching of winding connections). When connected in Delta, the motor can operate a full power. This starting method was often used on large air compressors here in the USA for motors of 300HP to 500HP. The unloader valves on the compressor are open when in start mode thereby keeping the load on the motor down, and allowing it to come up to full speed. Then when at full speed, the winding are mechanically reconnected in Delta configuration and the compressor is off and running as desired. The advantage to this method of stating is keeping the starting current down to a lower more tolerable level. I have no idea why the previous lathe owner would want to run the motor Wye connected unless it was because of the voltage available. So getting back to the problem as noted, I agree with the comment that the motor was in Wye connection as as such had not ability to handle load. I did not see anything in the motor terminal box photographs which would suggest the previous owner used a Wye-Delta starter since all six leads of the motor would have to be brought out of the terminal box and connected to the starter. Those pictures showed the motor wiring was Wye connected for sure.
