On CNC lathes, four standard threads can be turned: metric, foot, modulus, and diameter control. Regardless of which thread is turned, the lathe spindle and the CNC blade need to maintain a strict movement relationship: that is, each spindle rotates one revolution (such as the work rotates once), the CNC blade should move evenly by a pitch. The following is based on the analysis of various types of threads to enhance the mastery of various types of threads and facilitate the processing of various types of threads.

CNC lathe

First, the specification analysis of ordinary threads

Numerical control lathe processing also has many specifications for ordinary thread. The specification calculation analysis required for ordinary thread processing mainly includes the following two levels:

1. Diameter of steel parts before thread processing
Following the shrinkage of the thread profile, the diameter of the works before threading is D/D-0.1P, that is, the major diameter of the thread minus 0.1 pitch, usually based on the material deformation potential, which is 0.1 to 0.5 smaller than the major diameter of the thread.

2. Thread processing feed
The amount of thread increase can refer to the bottom diameter of the thread, which is the last position of the thread cutter. The minor diameter of the thread is: large diameter-2 times the tooth height; tooth height = 0.54P (P is the pitch)
The amount of cutting for thread processing should continue to decrease, and the actual amount of cutting is selected based on the CNC blade and work material.

Second, the tool selection and tool setting of general thread CNC blades

If the turning tool is installed too high or too low, when the tool is eaten to a certain thickness, the flank of the milling cutter will bear against the steel part, increasing sliding friction, and even bending the works, resulting in a biting condition; too low, then Cutting is difficult to discharge. The axial force of the turning tool is located at the center of the works. In addition, the gap between the traverse screw and the nut is too large, which causes the thickness of the tool to continue to automatically tend to become deeper, and then the work is extended to show the tool. At this time, the height-width ratio of the turning tool should be adjusted immediately so that the cutting edge is equidistant from the center line of the works(the tool can be adjusted with the aid of the tail stock center). When boring and semi-finishing turning, the cutting edge is 1% D above the center of the works (D represents the diameter of the works to be processed).

Works clamping is not stable. The rigidity of the works itself cannot bear the cutting force during cutting, so that excessive deflection is formed, and the center height of the turning tool and the work is changed (the work is raised), resulting in a sudden increase in cutting thickness and gnawing Knife, the works should be clamped firmly at this time, and the tail stock center can be used to improve the rigidity of the works.

CNC lathe

General thread tool setting methods include trial-cutting tool setting and automatic tool setting with a tool setting instrument. The tool can be directly used for trial cutting with a CNC blade. G50 can also be used to set the works zero point and works movement to set the works zero point for tool setting. The tool setting standard for thread machining is not very high, especially the Z-direction tool setting has no strict limit, which can be determined according to the programming standard.

Third, programming and processing of ordinary threads

In the current CNC lathe processing, thread turning usually has three processing methods: G32 straight cutting method, G92 straight cutting method and G76 oblique cutting method. Because the turning methods are different, the programming methods are different. The processing deviation is also different. We must carefully analyze the operation and application, and strive to process high-precision parts.

1. G32 straight-forward turning method, because the two edges work together, the cutting speed is very high, and the cutting is difficult, so the two turning edges are easy to be damaged during turning. When turning a thread with a large pitch, because the turning depth is very large, the cutting edge is damaged rapidly, which leads to a deviation in the pitch diameter of the thread; however, the processed tooth profile has high precision, so it is usually used for small pitch thread processing. Because the tool moves and chips are carried out by programming, the processing procedure is longer; considering that the cutting edge is easy to wear, it is necessary to ensure frequent measurement during processing.

2. The G92 linear turning mode optimizes the programming and increases the speed compared to the G32 console command.

3. G76 oblique cutting method, considering that it is one-sided cutting, the cutting edge is easy to be damaged and damaged, so that the processed thread surface is not straight, the sharp knife angle changes greatly, and the tooth profile precision is not good. But because it works with one side edge, the load of the CNC blade is small, chip removal is easy, and the turning thickness is decreasing.

CNC lathe

Therefore, this processing method is usually suitable for large pitch thread processing. Because this processing method is easy to remove chips and the cutting edge processing conditions are good, this processing method is more convenient when the thread precision is not high. When machining a thread with a higher precision and a high level, you can choose to use two-cut machining. First, use the G76 machining method to do the rough turning, and then use the G32 machining method to finish turning. But pay attention to the accuracy of the starting point of the tool, otherwise it is easy to buckle randomly and cause the parts to be scrapped.

4. After the thread processing is successful, you can carefully observe the thread profile to determine the thread quality and timely improvement measures. When the thread crest is not sharp, the cutting amount of the lifting knife will increase the major diameter of the thread. The increase depends on the ductility of the material. When the tooth top has been sharpened, the cutting amount of the knife is increased, and the large diameter is reduced in proportion. According to this feature, the cutting amount of the thread must be treated correctly to avoid scrapping.