Straight advance method: The straight advance method is also called the grooving method. When turning the thread, only the middle carriage is used for lateral (perpendicular to the guide rail direction) feed, and thread turning is completed in several strokes. Although this method can obtain a relatively correct tooth profile, the operation is also very simple, but because the three cutting edges of the tool participate in the cutting at the same time, the vibration is relatively large, the flank is easy to pull out burrs, it is not easy to obtain a better surface quality, and it is easy to produce The phenomenon of piercing, therefore, it is only suitable for turning trapezoidal threads with a small pitch:
Left and right cutting method: When turning the trapezoidal thread with the left and right cutting method, in addition to using the middle carriage scale to control the lateral feed of the turning tool, at the same time, the small carriage scale is also used to control the left and right micro feed of the turning tool until the tooth profile is completely turned. . When threading with the left and right cutting method, since one of the two main cutting edges of the turning tool is performing single-sided cutting, it avoids the simultaneous cutting of three edges, so it is not easy to cause the phenomenon of cutting. In addition, when finishing turning, try to choose a low speed (v=4～7m/min), and pour cutting fluid, generally you can get a good surface quality. In the actual operation process, students should control the left and right feeds while observing the chip condition based on actual experience. When the discharged chips are very thin, smoothing can be used to make the surface of the screw thread smooth and precise. . However, the operation of the left-right cutting method is more complicated. When the small carriage left and right micro-feeds are prone to errors due to the influence of the empty stroke, and the middle carriage and the small carriage feed at the same time, the size and ratio of the two feeds are not fixed. The cutting amount is not easy to control, and the tooth shape is not easy to be turned clearly. Therefore, the left-right cutting method requires high proficiency and cutting skills of the operator, and is not suitable for beginners to learn and master:
Straight groove turning method: When turning the trapezoidal thread with the straight groove method, a rectangular thread turning tool with a bit width slightly smaller than the width of the alveolar base is generally used, and the thread is roughed to the small diameter by the horizontal straight forward method (0.2～0.3mm on each side) The margin), and then use a fine turning tool for trimming. This method is simple, easy to understand and easy to master, but when turning a trapezoidal thread with a larger pitch, the tool is easy to break due to its narrow head and insufficient strength: the cutting groove is deep, chip removal is not smooth, resulting in accumulation of Chips "smash off" the cutter head: the feed rate is small and the cutting speed is low, so it is difficult to meet the needs of turning trapezoidal threads:
Turning stepped groove method: In order to reduce the damage of the cutter head during the "straight groove method" turning, we can use the turning stepped groove method. This method also uses a rectangular thread turning tool for grooving, but instead of cutting directly to the small diameter size, it is divided into several tools to cut into stepped grooves, and finally a fine turning tool is used to trim to the specified size. In this way, the cutting and chip removal is smoother and the method is relatively simple, but it is not easy to align the spiral straight groove when changing the tool, it is difficult to ensure the correct tooth shape, and the phenomenon of inverted teeth is easy to occur.
To sum up: In addition to the straight forward method, the other three turning methods can reduce or avoid the simultaneous cutting of three edges to varying degrees, so that the chip evacuation is smoother, and the force and heat of the tool tip are improved, so that vibration is less likely to occur. It can also increase the cutting amount and improve the thread surface quality. Therefore, the left and right cutting method, the turning straight groove method and the turning step groove method have been widely used. However, for beginners, the above three turning methods are difficult to master and cumbersome to operate, which needs to be made easier and simplified. Through years of teaching and practice, it has been discovered that "layered turning of trapezoidal threads" can make it easy for students to understand and master.