How to choose milling tools for machining threaded holes?

Threading is the most common method of connecting mechanical parts, and threaded hole machining is often at the end of the entire production process. Once the machining is not qualified, it can lead to the scrapping of the component or more complicated reprocessing. Therefore, it puts forward higher requirements for the safety of the process. There are various types of cutting tools for processing threaded holes, including thread turning tools, taps, extrusion taps, thread milling cutters, and so on. How to choose the correct machining tool? The selection of cutting tools is actually the choice of machining methods, and the tools used for each machining method are different. There are several common methods for machining threaded holes: tapping, turning, extrusion molding, and thread milling. Next, let's first understand the advantages, disadvantages, and limitations of various processing methods. In actual production, we can analyze which cutting tools should be used for processing from a technical and economic perspective based on the characteristics of these processing methods.

1. Attack teeth

Tapping is a widely used method in threaded hole machining. It can determine the formation of threads with the help of the geometric shape of the cutting tool, so there is no need for specialized machine tools during processing. It can be used on ordinary machine tools, production line special machines, and machining centers. The process of tapping teeth is that the tap first rotates forward for cutting, and then reverses when it reaches the bottom of the thread, leaving the workpiece and cutting in a very narrow space to discharge the chips. For different processing conditions and materials, the type of tap selected is also different. Tap tapping is commonly used in small diameter and large-scale production.

2. Turning machining

Turning machining threads is the use of indexing inserts for turning machining. Triangular threads are commonly used in production, and the shape of the cutting part of the thread turning tool should match the axial cross-section of the thread. When turning, for each rotation of the workpiece, the turning tool must move longitudinally by one lead (single head thread, lead=pitch) in order to machine the correct thread. There are three commonly used methods for car triangle threads:

A、 Straight in French car thread. When threading, after testing and checking that the workpiece and pitch meet the requirements, feed radially perpendicular to the workpiece axis and repeat multiple times until the thread is threaded properly. This turning method is more accurate in shaping teeth. Due to the simultaneous cutting of both edges of the turning tool and poor chip removal, the tool is subjected to high stress and is prone to wear, causing chips to scratch the surface of the thread.

B、 Diagonal French car thread. When the pitch of the workpiece is greater than 3MM, the oblique cutting method is generally used to machine the thread. The oblique cutting method is that the turning tool advances radially along one side of the thread profile while making axial feed. After multiple passes, the thread is processed, and finally the straight cutting method is used to ensure the accuracy of the thread profile angle.

C、 Left and right knife technique. In a regular lathe, this method uses the scale of the transverse drag plate to control the vertical feed of the threaded turning tool, and uses the scale of the small drag plate to control the micro feed of the turning tool on both sides. When the thread is close to being cut, use a nut or thread gauge to check whether the thread size and machining accuracy are qualified. This method is easy to operate, so it is widely used.

Turning machining threads is generally applied to larger diameter holes, and the workpiece can be firmly clamped on the lathe for rotational machining.