Backing off device of tap-grinding machine

The utility model discloses a relief grinding device for a tap grinding machine, comprising a grinding wheel carrier, a head holder and a tailstock, wherein, the grinding wheel carrier is connected to a control mechanism which controls a grinding wheel to only perform whirling motion and feeding motion; the head holder and the tailstock are arranged on a rocker which is positioned on a work top of the tap grinding machine; both ends of the rocker are respectively fixed on shells of the work top and the relief grinding device of the tap grinding machine through cross spring boards and connected with bearing supports on a control mechanism of the rocker; a camshaft of the control mechanism of the rocker is connected with a power shaft through a gear pair. The grinding wheel of the relief grinding device only performs whirling motion and feeding motion, and workpieces are arranged between tips of the head holder and the tailstock which are positioned on the rocker and rotate and simultaneously swing along with t