1. Transmission principle
When turning threads, in order to obtain accurate threads, it is necessary to use the screw rod to drive the tool holder feed, so that every turn of the workpiece, the tool moving distance is equal to the pitch.
2. Thread turning tool and installation
The guarantee of tooth shape Angle A depends on the grinding and installation of the threading tool.
Requirements for grinding of screw turning tool:
1) The turning tool's sharp Angle is equal to the tooth shape Angle of the axial section of the thread;
2) Front Angle 0=0°, coarse cutting thread in order to improve the cutting conditions, can be used with a positive front Angle turning tool (0=
5° ~ 15°).
Installation requirements for thread turning tool:
1) The tool tip must be equal to the rotation center of the workpiece.
2) The bisector of the cutter's sharp Angle must be perpendicular to the axis of the workpiece. Therefore, use the knife template.
3. Adjustment and installation of machine tools
After the lathe tool is installed, the lathe should be adjusted, according to the size of the workpiece pitch, find the lathe sign, select the position of the feed box handle, take off the smooth rod feeding mechanism, change to the screw drive. Select a low spindle speed so that the cutting is smooth and there is sufficient time to return the tool. In order to make the tool move evenly and steadily, it is necessary to adjust the gap between the guide rail of the horizontal slide plate and the gap between the screw rod and the nut of the small tool holder.
In the turning process, the workpiece on the spindle if there is a small loose, that is, the shape of the thread or the pitch is not accurate, so the workpiece must be clamped firmly.
4. Operation method
The thread diameter is guaranteed by controlling the total cutting depth of multiple feeds. The cutting depth of each thread should be small, and the total cutting depth can be roughly controlled by the sliding plate dial according to the calculated thread working tooth height (working tooth height =0.54× the pitch of the workpiece, in mm), and measured with the help of a thread gauge.
There are three ways to make triangular threads, namely, straight feed method, left and right cutting method and oblique cutting method.
(1) Direct progress method
Use a middle slide to feed, and cut both blades and tips at the same time. This method is easy to operate, the tooth shape out of the car is clear, the tooth shape error is small, but the turning tool stress, poor heat dissipation, chip removal difficult, knife tip easy to wear. Suitable for machining threads with pitch less than 2mm, and fine turning for high-precision threads.
(2) Left and right cutting method
The feature of the left and right cutting method is to make the turning tool have only one blade to participate in cutting. At the same time of each deep cutting, a small knife rest is used to move a short distance to the left and right. Such repeated cutting several times, the car to the last 1 ~ 2 knife, still use the direct feed method, to ensure the correct shape, the root is clear. This method is suitable for machining threads with large pitch.
(3) Oblique cutting method
Turn the small tool holder to an Angle, so that the turning tool along the right side of the thread parallel to the car feeding, so that there is basically only one cutting edge in the two cutting blades. This cutting force is small, heat dissipation and chip discharge conditions are better, cutting can be larger, higher productivity. However, it is not easy to produce a clear tooth shape, and the tooth shape error is large. Generally suitable for coarse car with large pitch thread.
Step 5 Avoid "unbuttoning"
When the screw thread, the movement of the turning tool is driven by the engagement of the cutting nut and the screw, and a thread groove needs to go through several times to complete. When the car after a knife another car knife, must ensure that the turning tool always fall in the thread groove has been cut out, otherwise it is called "disorderly buckle", resulting in scrap workpiece.
The main reason for the "disorderly buckle" is that the screw pitch P of the lathe and the workpiece is not an integer times the pitch P. When P wire /P work = integer, the "opening nut" can be opened after each cutting, and the turning tool will exit horizontally and the tool rest will be rolled back longitudinally without "disorderly buckle". If P wire /P work ≠ integer, the "opening nut" cannot be opened and the knife rest can be rolled back. Instead, the "opening nut" can only be opened once after the turning tool goes, and the turning tool can only be backed out and the reversing workpiece can be reversed to make the turning tool return to the starting position. Then adjust the cutting depth of the turning tool, then continue to drive in turn, the main shaft is turning, for the next cutting. Since the "split nut" is not opened, the split nut is always engaged with the screw, so that the turning tool tip can be precisely cut in a fixed spiral groove, without "random buckle".
6. Measurement of triangular threads
The common gauge used to check triangular threads is the thread gauge. Thread gauge is a comprehensive test gauge, divided into plug gauge and ring gauge. Plug gauge to check the internal thread, ring gauge to check the external thread, and by gauge, stop two pieces of a set. Thread workpiece is qualified only in the case that the gauge can pass and the stop gauge can't pass, otherwise the parts are unqualified products.
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