1. Transmission principle When turning threads, in order to obtain accurate threads, the screw rod must be used to drive the tool holder to feed, so that the tool moves a distance equal to the thread pitch every time the workpiece rotates. 2. Thread turning tool and installation The guarantee of the tooth profile angle α depends on the sharpening and installation of the thread turning tool. Requirements for thread turning tool sharpening: 1) The tool nose angle of the turning tool is equal to the tooth profile angle α of the axial section of the thread; 2) The rake angle γ0=0°, in order to improve the cutting conditions for rough thread turning, a turning tool with a positive rake angle (γ0= 5°～15°). Requirements for thread turning tool installation: 1) The tool tip must be at the same height as the workpiece rotation center. 2) The bisector of the tool nose angle must be perpendicular to the workpiece axis. Therefore, use the tool setting template to set the tool. 3. Machine tool adjustment and installation After the turning tool is installed, the machine tool should be adjusted. According to the size of the workpiece pitch, look for the lathe label, select the position of the handle of the feed box, disengage the polished rod feeding mechanism, and change it to the screw drive. Select a lower spindle speed for smooth cutting and sufficient time for tool retraction. In order to make the tool move evenly and smoothly, it is necessary to adjust the gap between the guide rail of the sledge plate and the gap between the screw and the nut of the small knife holder. During the turning process, if the workpiece is slightly loose to the spindle, it will lead to inaccurate thread shape or pitch, so the workpiece must be clamped firmly. 4. Operation method The pitch diameter of the thread is guaranteed by controlling the total depth of cut of multiple feeds. When threading, the depth of cut each time should be small, and the total depth of cut can be roughly controlled by the dial of the middle slide plate according to the calculated thread working tooth height (working tooth height=0.54×the pitch of the workpiece, and the unit is mm), and measured with the help of a thread gauge. There are three methods for turning triangular threads, namely straight forward method, left and right cutting method and oblique cutting method. (1) Straight forward method The knife is fed by the middle slide, and the two blades and the tip of the knife are cut at the same time. This method is easy to operate, the tooth shape produced by the car is clear, and the tooth shape error is small, but the turning tool is stressed, the heat dissipation is poor, the chip removal is difficult, and the tip of the tool is easy to wear. It is suitable for processing threads with a pitch less than 2mm and fine turning of high-precision threads. (2) left and right cutting method The characteristic of the left and right cutting method is that only one blade of the turning tool participates in the cutting, and at the same time of each cutting depth, the small tool holder is used to move a small distance to the left and right. Repeat the cutting several times in this way, and when the car reaches the last 1-2 cuts, the straight-forward method is still used to ensure that the tooth shape is correct and the root of the tooth is clear. This method is suitable for processing threads with larger pitches. (3) Oblique cutting method Turn the small tool holder at an angle, so that the turning tool feeds in parallel to the right side of the thread to be turned, so that basically only one of the two cutting edges of the turning tool cuts. The cutting force of this method is small, the heat dissipation and chip removal conditions are better, the cutting amount can be larger, and the productivity is higher. However, it is not easy to produce a clear tooth shape, and the error of the tooth shape is relatively large. It is generally suitable for rough turning of larger pitch threads. 5. Avoid “chaotic buckling” When threading, the movement of the turning tool is driven by the engagement between the split nut and the screw rod, and a thread groove needs to be completed through multiple tool passes. When one tool is turned and another tool is turned, it must be ensured that the turning tool always falls in the thread groove that has been cut out, otherwise it is called “chaotic buckling”, which will cause the workpiece to be scrapped. The main reason for “chaotic buckling” is that the pitch P of the lathe screw and the pitch P of the workpiece are not integer multiples. When P wire/P work = integer, after each tool pass, the “opening and closing nut” can be opened, the turning tool is withdrawn horizontally, and the tool holder is shaken vertically, without “chaos buckling”. If P wire/P ≠ integer, you can’t open the “opening and closing nut” and swing back the tool holder, but only after the turning tool moves once, do not open the “opening and closing nut”, just withdraw the turning tool, reverse the workpiece and reverse, so that the turning tool returns to the initial position. Then adjust the cutting depth of the turning tool, and then continue to drive along the car, the main shaft rotates forward, and proceed to the next tool pass. Because the “split nut” is not opened, the split nut is always engaged with the screw mandrel, and the tip of the turning tool will be accurately cut in a fixed spiral groove, so that “chaotic buckling” will not occur. 6. Measurement of triangular thread A common measuring tool for inspecting triangular threads is a thread gauge. Thread gauge is a comprehensive inspection measuring tool, which is divided into two types: plug gauge and ring gauge. The plug gauge is used to inspect the internal thread, and the ring gauge is used to inspect the external thread, and a pair is composed of a pass gauge and a stop gauge. The threaded workpiece is qualified only if the pass gauge can pass but the stop gauge cannot pass, otherwise the parts are unqualified.  

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