Semi-automatic thread grinding device for lathe

The invention discloses a semi-automatic thread grinding device which is applied to the field of machining, is driven by a lathe and is convenient to operate. The semi-automatic thread grinding device is mainly structurally characterized in that a spring outer barrel of the thread grinding device is driven by an eccentric wheel to lift, and a knife grinding head is always meshed with a workpiece thread with proper force by an adjusting spring; when the device works, an outer box body moves forwards through rotation of a workpiece so as to compress a reset spring, a handle is rotated to enable a gear to be separated from a rack when thread grinding is finished, the knife grinding head returns to the initial position under the action of the reset spring to conduct grinding operation of the next period, and the initial position of the outer box body can be changed by adjusting a knife rest, so that the size range of the ground workpiece is enlarged, a worker only needs to rotate the eccentric wheel and the handl