1) Incorrect corner
Turning tool angle when sharpening is not correct, i.e., turning in two cutting edge flank angle inconsistent with threading the angle between the projection surface of the base, angle of thread lead-out processing is incorrect. Solution: When sharpening the turning tool, you must use an angle ruler or template to check, and get the correct angle of the teeth. The method is: the model or angle ruler should be parallel to the front of the turning tool, and then check with the light transmission method. Commonly used metric thread angles: triangular thread 60°, trapezoidal thread 30°, worm 40°.
2) Radial rake angle is not corrected
In order to make the turning tool smoothly, reduce the surface roughness, and reduce the phenomenon of built-up edge, often grinding the radial rake angle, which causes the cutting on both sides of the turning tool does not coincide with the workpiece axially, making the thread teeth of the workpiece out of the workpiece. The angle is larger than the tool nose angle of the turning tool. The larger the radial rake angle, the greater the error of the angle of the tooth profile. At the same time, the thread profile that is turned out is not a straight line in the axial profile, but a curve, which affects the fitting quality of the thread pair. Solution: When sharpening the thread of the thread cutter with large radial rake angle, the tool nose angle must be corrected by the angle between the two blades of the turning tool. In particular, the thread with higher machining accuracy has the following calculation method:
In the formula, εr is the angle between the two blades of the turning tool; rp is the radial rake angle; α is the angle of the teeth.
3) Excessive profile angle during HSS cutting
In the high-speed cutting of the thread, due to the pressing force generated by the turning tool on the workpiece, the tooth shape will be enlarged and the workpiece will expand. Therefore, when sharpening the turning tool, the angle between the two blades should be appropriately reduced. Small 30'. In addition, the major diameter of the workpiece before turning the external thread is generally smaller than the nominal size (about 0.13p).
4) The tool is not installed correctly
The incorrect installation of the turning tool means that the symmetrical centerline of the two cutting edges of the turning tool is not perpendicular to the axis of the workpiece, resulting in a tilted tooth angle (commonly known as inverted tooth). Solution: Use a ruler or template to install the turning tool so that the symmetrical centerline is perpendicular to the workpiece axis and the tool tip is at the same height as the center of the workpiece.
5) Tool wear
After the tool was worn out, it was not sharpened in time, resulting in the fact that the two sides of the tooth profile were not straight but curved or "broken". Solution: Reasonably choose the cutting amount and sharpen the knife after wear.
6) The pitch (or lead) is incorrect
A thread length is incorrect. The reason for the incorrect length of the thread is that the exchange gear has been incorrectly calculated or assembled. If the position of the handle in the feed box or carriage box is wrong, check the position of the handle of the feed box or check the hanging wheel.
B thread is partially incorrect. The reason that the thread is partially incorrect is that the screw and the spindle of the lathe are too large, the handwheel of the carriage is not balanced, and the opening and closing nut gap is too large. Solution: If the screw is caused by axial turbulence, adjust the adjustment round nut at the joint between the screw of the lathe and the feed box to eliminate the axial clearance of the thrust ball bearing at the joint; if it is the axial direction of the spindle Caused by the movement, can adjust the spindle rear adjustment nut to eliminate the axial clearance of the thrust ball bearing; if it is the opening and closing nut of the carriage box and the screw shaft caused by improper meshing, the opening and closing nut can be trimmed and adjusted. The nut gap; if it is unbalanced, the slide box can be pulled out to make it rotate with the rotating shaft evenly.
C Turning the process of opening and closing nut lift automatically lead to incorrect pitch. Solution: Adjust the opening and closing nut setting to reduce the gap properly, control the opening and closing nut to lift, or use heavy objects to hang on the handle of the opening and closing nut.