We undertake thread machining on numerical control lathe when, use a cutting tool to undertake cutting normally. When machining big pitch whorl, because cutting tool has worn away fast, dimension of the whorl after can causing cutting to machine changes precision of big, whorl is low. Through old exploration, we fumble when giving a kind to machine whorl in the cutting on numerical control lathe, divide lathe tool of thick, essence to undertake. In machining a process, wear away when thick car razor blade after the limit, change fine vehicle bit to thick car cutting tool, fine vehicle cutting tool changes new bit afresh. Can be in so make sure whorl cutting machines precision while, also reduce cutting tool cost. This method key depends on pair of thick, essence pair of knife precision of thread tool. 1, operation method The circle outside mixing workpiece end panel cutting one knife (end panel is flat, ) of the circle outside the car, d of diameter of the circle outside be being measured next, change whorl of cutting of knife of thick car whorl. Specific means is as follows: rough machining cutting tool (after T0X00) shakes with the hand pulse generator is machined to cutting first outside round D. Shake with the hand pulse generator is versed in to shake-out in Z axis square, input D is worth (axis of this knife X is over to the knife) . Record the specific data that next X axes show. On the data that shakes with the hand pulse generator shows a record in X axis place to negative direction feed 1 ～ 2mm. Shake with the hand pulse generator loses directional feed in Z axis likewise, cutting tool cutting arrives workpiece can. Input Z0(Z axis is over to the knife) . At this moment thick car thread tool ends to the knife. Be opposite again by this method whorl finish machining, operation measure and thick car cutting tool agree completely to knife method. Won’t produce chaos to discount an appearance in cutting process so. Although more machines cutting tool cutting, won’t produce chaos to discount an appearance as much. 2, note (1) is opposite cutting tool each when X axis, the number that the machine tool shows each are not identical. Must have recorded the real data of each cutting tool. After exiting X axis, the data of feed of axis of X of cutting tool of many whorl cutting must identical, cannot have difference. (2) is in the process to the knife, when be close to workpiece X axis and Z axis, proposal hand shakes pulse generator had better choose feed 0.001mm to block.