Thread cutting generally refers to the method of machining threads on a workpiece with a forming tool or a grinder, mainly including turning, milling, tapping, threading, grinding, and 

whirlwind cutting. When turning, milling, and grinding threads, the machine tool's transmission chain ensures that the turning tool, milling cutter, or grinding wheel moves one lead accurately 

and evenly along the axial direction of the workpiece for each rotation of the workpiece. When tapping or threading, the tool (tap or die) and the workpiece make relative rotational motion, 

and the first formed thread groove guides the tool (or workpiece) to move axially.

Thread turning refers to turning threads on a lathe with a forming turning tool or a thread combing tool. Turning threads with a forming turning tool is a common method for single-piece and 

small-batch production of threaded workpieces due to its simple tool structure; turning threads with a thread combing tool has high production efficiency, but the tool structure is complex 

and is only suitable for turning short threaded workpieces with fine teeth in medium and large-scale production. The pitch accuracy of trapezoidal threads on ordinary lathes can generally 

only reach 8 to 9 levels; processing threads on specialized thread lathes can significantly improve productivity or accuracy.

Thread milling refers to milling with disc milling cutters or comb milling cutters on thread milling machines. Disc milling cutters are mainly used to mill trapezoidal external threads on 

workpieces such as screws and worms. Comb milling cutters are used to mill internal and external ordinary threads and tapered threads. Since they are milled with multi-blade milling cutters 

and the length of their working parts is greater than the length of the processed threads, the workpiece only needs to rotate 1.25 to 1.5 turns to complete the processing, and the productivity 

is very high. The pitch accuracy of thread milling can generally reach 8 to 9 levels, and the surface roughness is R5 to 0.63 microns. This method is suitable for batch production of threaded 

workpieces with general accuracy or rough processing before grinding.

Thread grinding is mainly used to process precision threads of hardened workpieces on thread grinders. According to the different cross-sectional shapes of the grinding wheels, there are two 

types of grinding: single-line grinding wheel and multi-line grinding wheel. The pitch accuracy that can be achieved by single-line grinding wheel grinding is 5 to 6 levels, the surface 

roughness is R1.25 to 0.08 microns, and the grinding wheel dressing is relatively convenient. This method is suitable for grinding precision screws, thread gauges, worms, small batches of 

threaded workpieces and precision hobs for relief grinding. Multi-line grinding wheel grinding is divided into longitudinal grinding and cut-in grinding. The grinding wheel width of the 

longitudinal grinding method is less than the length of the thread to be ground, and the grinding wheel can grind the thread to the back size by moving longitudinally once or several times. 

The grinding wheel width of the cut-in grinding method is greater than the length of the thread to be ground, and the grinding wheel radially cuts into the surface of the workpiece. The 

workpiece can be ground after about 1.25 turns. The productivity is high, but the accuracy is slightly lower, and the grinding wheel dressing is relatively complicated. Cut-in grinding is suitable 

for relief grinding of large batches of taps and grinding of certain fastening threads. Thread grinding is to use a nut-type or screw-type thread grinding tool made of softer materials such as 

cast iron to perform forward and reverse rotation grinding on the parts of the machined threads on the workpiece where there is a pitch error to improve the pitch accuracy. Hardened internal 

threads are usually ground to eliminate deformation and improve precision.