Ⅰ.the definition of turning thread:

Turning thread is a method of machining thread with lathe. When turning thread, in order to obtain the correct thread shape, the tool tip must be equal to the center of the workpiece, the tool tip Angle is equal to the tooth Angle, and the turning tool feed direction must be strictly consistent with the workpiece rotation direction.

 

Ⅱ、Standard for turning thread:

1, the national standard thread standard refers to the thread standard formulated by China, mainly including the following:

① Common thread GB/T 192-2003 is the Chinese national standard, the full name is "Common thread basic size". The standard specifies the basic dimensions of the common thread (M series), including the diameter and pitch series, basic dimensions, tolerances, limit deviations and marking.

The GB/T 192-2003 standard is suitable for mechanical fastening connections for general purposes, such as the design, manufacture and inspection of bolts, nuts, screws, studs and other fasteners. This standard plays an important role in ensuring the interchangeability, reliability and economy of threaded connections.

2 Metric taper thread GB/T 1415-2008 standard, the standard specifies the tooth Angle of 60°, the tooth type, basic size, tolerance and marking of the metric seal thread. The internal thread has two kinds of cone internal thread and cylindrical internal thread, and the external thread has only one kind of cone external thread. The internal and external threads can be formed into two types of sealing fit: the internal taper thread and the external taper thread form a "cone/cone" fit; The cylindrical internal thread and the taper external thread form a "column/cone" fit. This standard is applicable to general sealing threaded connections on pipes, valves, pipe joints, stoppers and other products. When assembling, it is recommended to add a suitable sealing medium in the thread pair, such as sealing tape, sealant, etc.

(3) GB/T 12716-2011 standard for 60° taper pipe thread specifies the tooth type, basic dimensions, tolerances, marks and gauges of NPT and NPSC pipe threads with a seal Angle of 60° and thread pairs themselves.

The 60° taper pipe thread contains NPT (taper thread, divided into internal thread NPTM and external thread NPTF) and NPSC (cylindrical internal thread). Internal and external threads can be formed into two types of matching: taper internal thread and taper external thread (NPTF and NPTM) group of matching; Cylindrical internal and taper external threads (NPSC and NPTM) are used together. This standard applies to sealed threaded connections of pipes, valves, fittings, plugs and other piping accessories.

The current effective standard for trapezoidal thread is GB/T 5796-2016. The standard specifies the basic tooth type, design tooth type, basic dimensions, tolerances, marks and gauges of trapezoidal thread. Trapezoidal thread is mainly used for transmission and fastening connection, which has the advantages of high transmission efficiency, good neutrality and high root strength.

2. The American standard thread standard refers to the thread standard developed by the United States, which mainly includes the following:

UN (Unified National Thread) : This is a unified thread standard for mechanical connections and fasteners. The UN thread has a 60° profile Angle and the pitch is expressed in teeth per inch.

NPT (National Pipe Thread) : This is a taper pipe thread standard for pipe connection. The NPT thread has a 60° profile Angle and the pitch is expressed in teeth per inch.

(3) UNC (Unified National Coarse Thread) : this is a coarse unified thread standard with large pitch, used in cases where quick connection and disassembly are needed.

④ UNF (Unified National Fine Thread) : This is a fine tooth unified thread standard, small pitch, for occasions requiring high precision and strength.

These American thread standards are widely used in the United States and other countries for machinery, plumbing, automotive, aerospace and other fields. When using American standard thread, it is necessary to select the appropriate standard according to the specific application scenario, and design and processing in accordance with the standard requirements.

3, the following are some common British standard thread standards:

BSW (British Standard Whitworth Thread) : BSW thread is a Wyeth thread standard, mainly used in the United Kingdom and other Commonwealth countries. It has a 55° tooth profile Angle, and the pitch is expressed in teeth per inch.

BSP (British Standard Pipe Thread) : BSP thread is a thread standard for pipe connection, including BSPP (parallel pipe thread) and BSPT (conical pipe thread) two types. The BSP thread has a 55° profile Angle and the pitch is expressed in teeth per inch.

BSF (British Standard Fine Thread) : BSF thread is a fine Wyeth thread standard, mainly used in the United Kingdom and other Commonwealth countries. It has a profile Angle of 55° and a finer pitch than the BSW thread.

④ UNF (Unified National Fine Thread) : UNF thread is an American unified fine thread standard, which is also adopted by the United Kingdom. It has a 60° tooth profile Angle, and the pitch is expressed in teeth per inch.

These British thread standards are widely used in the United Kingdom and other Commonwealth countries for machinery, plumbing, automotive, aerospace and other fields. When using British standard thread, it is necessary to select the appropriate standard according to the specific application scenario, and design and processing in accordance with the standard requirements.

 

Ⅲ、What kinds of turning threads are divided into:

Thread turning is the method of processing threads on the lathe with a turning tool, which is mainly divided into the following types:

1. Direct drive method: When turning, the tool is fed in the direction perpendicular to the axis of the workpiece, and the thread is turned in one stroke. This method is suitable for turning triangular threads with small pitch.

2. Oblique advance method: When turning, the turning tool is fed along the direction of a certain Angle with the workpiece axis, and the turning of the thread is completed in multiple strokes. This method is suitable for turning triangle thread and trapezoidal thread with larger pitch.

3. Left and right cutting method: When turning, the turning tool is fed alternately along the direction of a certain Angle with the workpiece axis, and the turning of the thread is completed in multiple strokes. This method is suitable for turning triangle thread and trapezoidal thread with larger pitch.

4. Stratified cutting method: When turning, the turning tool only turns a very shallow thread shape after each feed, and then gradually deepens, and the turning of the thread is completed in multiple strokes. This method is suitable for thread with high turning precision.

 

 

Ⅳ、Form of turning thread:

1. Internal thread turning: Using the tool to turn the internal thread in the inner hole of the workpiece.

2. External thread turning: Using the tool to turn the external thread on the outer cylinder of the workpiece.

3. Left-hand thread turning: Use the tool to turn the left-hand thread, that is, the thread that rotates counterclockwise.

4. Right-hand thread turning: Use the tool to turn the right-hand thread, that is, the thread that rotates clockwise.

5. Multi-thread turning: Using the tool to turn out multiple thread heads at the same time in one clamping.

6. Trapezoidal thread turning: Using the tool to turn out trapezoidal shape of the thread.

7. Rectangular thread turning: Use the tool to turn out the rectangular shape of the thread.

 

Ⅴ、Thread tool selection：

1. Thread type: It is necessary to determine the type of thread needed to be machined, such as triangle thread, trapezoidal thread, rectangular thread, etc.

2. Pitch and tooth Angle: pitch refers to the distance between two adjacent thread teeth, and tooth Angle refers to the Angle on both sides of the thread teeth. These parameters need to be determined according to the specific thread standards.

3. Thread accuracy: Thread accuracy refers to the dimensional accuracy and shape accuracy of the thread, usually expressed by tolerance. The desired level of thread accuracy needs to be determined according to the specific requirements of use.

4. Thread direction: It is necessary to determine the rotation direction of the thread, which is usually divided into two kinds: left and right.

5. Thread length: It is necessary to determine the effective length of the thread, that is, the actual length of the thread.

6. Surface quality: It is necessary to determine the surface quality requirements of the thread, such as surface roughness, hardness, etc.

7. Processing materials: Different materials require different tool materials and geometric shapes. For example, when processing steel parts, high-speed steel or cemented carbide tools are usually used, while when processing aluminum alloys, PCD tools are needed.

8. Machining accuracy: thread with high machining accuracy requires the use of higher precision tools, such as sharp edges and small tip radius tools.

9. Tool life: Tool life refers to the time that the tool can maintain good performance during processing. In general, the longer the tool life, the lower the processing cost.

10. Processing efficiency: Processing efficiency refers to the number of threads that can be processed per unit time. Generally speaking, the higher the processing efficiency, the lower the production cost.

Ⅵ、When choosing thread cutting tools, the following factors need to be considered：

1. Processing materials: Different materials require different tool materials and geometric shapes, for example, processing steel requires a tool with higher hardness, while processing aluminum alloy requires a sharp tool.

2. Thread type: Different thread types require different tools, for example, the processing of internal threads requires an internal thread tool, while the processing of external threads requires an external thread tool.

3. Tool size: The tool size needs to match the size of the thread processed to ensure processing accuracy and efficiency.

4. Tool material: Tool material needs to be selected according to processing materials and processing requirements, commonly used tool materials include high-speed steel, carbide, ceramics and so on.

5. Tool coating: Tool coating can improve the wear resistance and corrosion resistance of the tool, thereby extending the tool life and improving the processing efficiency.