1. Gnawing knives and slapping knives
(1) One of the reasons for the failure: the turning tool is installed too high. The turning tool clamping is too high, during cutting, due to the action of the main cutting force generated between the workpiece and the turning tool, the tip of the threaded turning tool is moved downward by the pressure of the workpiece, so that the turning tool is pressed to the maximum outer circle of the workpiece, so that the turning tool that is not deep in the original turning is more and more into the depth of the workpiece, so that the turning depth becomes deeper, and the turning force between the workpiece and the turning tool is further increased, resulting in the phenomenon of gnawing or punching.

(2) The second cause of failure: the clamping strength of the workpiece is not enough. When turning threads, the main turning force generated by the workpiece and the turning tool is the backlash force (i.e., depth of cut resistance).


(3) The third cause of failure: the rear angle of the turning tool is small. In rough turning, the relief angle is small but the turning is deep, and the amount of each tool is not easy to show. However, when the turning reaches a certain depth, the amount of tools gathers together to produce a large turning depth, so that the turning force between the tool and the workpiece increases suddenly, so the phenomenon of gnawing the knife is produced. When finishing, because the left and right turning method is used to turn (i.e., turning with small slide plate feed), the amount of cutter is small, so the cutting force between the workpiece and the turning tool is small, and the cutting force generated by the workpiece and the turning tool can not resist the resistance between the flank face and the workpiece, so that the turning tool can not turn the workpiece although the first few knives are fed in the first few cuts, and a certain knife in the back will finish the measurement of the first few knives at once, so as to produce the phenomenon of gnawing the knife.
Solution: The rear angles on both sides of the thread turning tool should be grinded larger. For right-hand threads, the left relief angle is larger than the right one.
(4) Cause of failure: incorrect turning method. When turning with the straight method, when the turning tool enters the workpiece deeply, if no measures are taken, the thread turning tool will have the phenomenon of three edges turning at the same time, resulting in excessive turning force on the turning tool and gnawing the knife, or even punching.

2. Random buckle
(1) One of the causes of failure: the ratio of the pitch of the lead screw of the lathe to the pitch of the workpiece is not an integer multiple. When threading, it takes several feeds to complete. If, on the second feed, the tip of the turning tool deviates from the spiral groove out of the previous feed car, there will be a tooth disorder (buckle). Because the ratio of the pitch of the lead screw and the pitch of the workpiece is not an integer multiple, when the first spiral groove is lifted after the first spiral groove is turned, when the second spiral groove is turned, the screw rod turns a turn, and the opening and closing nut is pressed again, and the workpiece does not turn the integer circle at this time, resulting in the turning tool can not enter the spiral groove that feeds the car out of the previous time, so there is a disorderly tooth (disorderly buckle) phenomenon.

(2) Cause 2: After reloading the tool in the middle of the process, the tooth is messy when turning. When turning threads, when the rough turning is completed, the tool has been severely worn, and the next step of fine turning cannot be carried out, and a new thread turning tool needs to be installed. The reloaded tool cannot be installed in the same position as the original turning tool, so it needs to be realigned. If the tool is not driven forward when the tool is set, but the knife is shaken into the spiral groove that has been turned in the parking state, when the turning will occur, the tooth will be messy.

3. The pitch is incorrect
(1) One of the causes of failure: the thread is incorrect on the entire workpiece. The reason is that when selecting the handle of the feed box, the correct position of the handle should be selected by mistake, so that when the handle of the feed box is wrenched, the position of the other pitch handle is wrongly selected, and the pitch of the car becomes other pitch.

(2) Cause of failure 2: local incorrectness. The reason may be that the axial movement of the lead screw and spindle is too large. The handwheel of the slip box rotates unbalancedly. The gap between the opening and closing nuts is too large. The opening and closing nuts are automatically lifted during turning.

4. The middle diameter is incorrect
(1) One of the causes of failure: the turning depth is incorrect, and the correct tooth height is not turned.

(2) the second cause of the failure: the wrong tool installation, so that the half angle of the two threads out of the car is not equal, resulting in a skewed tooth type (commonly known as inverted teeth), when the ring gauge is tested and turned, the ring gauge is not used to repair the tooth side, until the middle diameter of the car is wrong, and the gauge can be screwed in when the gauge can be screwed in.

5. The thread surface is rough

Solution: Use oil stone to refine the cutting edge of the turning tool to eliminate the burr generated when grinding; select a slower cutting speed and add sufficient cutting fluid when using high-speed steel turning tool; adjust the lathe saddle pressing plate and the middle and middle The inlay of the dovetail guide rail of the small slide plate ensures the accuracy of the clearance of each guide rail and prevents the vibration during cutting; the rear angle of the threaded fine turning tool should be sharpened, which not only makes the turning tool sharp, but also reduces the turning tool caused by the small rear angle during turning, so that the turning is smooth, reduces the friction between the turning tool and the workpiece, and makes the tooth surface quality better guaranteed.