Understanding Thread Machining: A Beginner's Guide

In the intricate manufacturing world, threads are crucial in providing the necessary coupling and connection between components. Understanding the nuances of thread machining is essential for producing high-quality products with optimal strength and durability. In this guide, we will study the fundamentals of machining threads, exploring different types of threads, terminology, methods for machining, key design tips, surface finishing techniques, and more.

If you are looking for more details, kindly visit BH.

Types of Threads:

Threads come in various forms, including internal and external threads. Internal threads within fasteners like nuts are machined using specific threading tools or taps. External threads, seen on bolts and screws, are created using lathes or die-cutting methods. Understanding the distinction between these types is crucial for effective thread machining.

Internal Threads:

Internal threads inside fasteners like nuts are machined using specialized tools such as taps, thread mills or single-tip threading tools. These threads accept screws and secure them within the workpiece. Select a tool with the appropriate nominal size to machine internal threads and fix the hole diameter according to the end-use application. Remove the actual threads from the CAD drawing during CNC machining, leaving only the major diameter profile. To calculate the minor diameter before tapping, consult hole size charts. It is critical to understand the percentage of thread that you will be tapping. A target is 70%, but different applications require different hole sizes. Also note that cut taps require different hole sizes than form taps.. After locating the center and drilling the hole to the calculated core-hole diameter, tap the hole&#;s edge with a tap tool and chamfer it with a 90-degree countersink.

External Threads:

External threads, which run along the outside of a fastener&#;s shaft like bolts, are typically produced using lathes. Any cylindrical rod can be turned in to create external thread profiles, with the tool selection based on the required pitch depth. External thread cutting begins with clamping the threading die, typically a round die, to the lathe machine. Before cutting, file and chamfer the edges at a 45-degree angle. Then, touch the workpiece edge with a cutting tool before revolving it along its length to create a continuous thread.

Terminology in Threads Machining:

Special taps offer several advantages over standard taps in certain applications:

• Root

  : The bottom surface of a thread groove, formed by two adjustable threads, can be either flat or rounded.

• Crest: 

  The outermost surface of a thread, created by the two sides of the thread, is known as the crest.

• Flank

  : The surface that connects a thread&#;s root and crest, making contact with its counterpart, is called the flank.

• Thread angle: 

  The angle formed by two adjacent flanks of two threads in the axial plane is called the thread angle.

• Thread depth: 

  The axial distance between a thread&#;s crest and root is defined as thread depth.

• Pitch: 

  The distance between two identical threads is known as the pitch.

• Helix angle: 

  The angle between the thread&#;s helix and a line that is normal to the axis of rotation is called the helix angle.

• Major diameter: 

  The diameter of the imaginary co-axial cylinder that touches the crest of the external thread (or root of the internal thread) is termed the major diameter.

• Minor diameter: 

  The diameter of the imaginary co-axial cylinder that touches the root of the external thread (or crest of the internal thread) is called the minor diameter.

• Pitch Diameter: 

  The average of the major and minor diameters is the pitch diameter.

Methods for Machining Threads:

Thread cutting is a fundamental process in creating screwed connections between components. Whether machining internal or external threads, ensuring they are securely inserted and locked together during assembly is crucial. Selecting the most suitable method for thread cutting involves considering various factors such as technical complexity, cost-effectiveness, time efficiency, accuracy, and tool availability.

CNC Milling:

CNC milling is a versatile method capable of cutting internal and external threads. It utilizes the circular motion of threading tools to create threads in a single lateral movement. This technique is particularly effective for larger holes, providing a high surface finish and precise dimensional consistency.

Thread Machining with Milling:

In thread milling, two popular tools are solid carbide and indexable tools. These tools feature parallel cutting teeth, unlike taps with helical setups. Multi-tooth thread machines can cut threads to deeper layers in a single turn around a hole. While carbide tools are preferred for smaller hole sizes due to their precision, indexable tools offer a cost-effective solution as only the cutter needs replacement.

Threads Machining with Lathe:

A single-point turning tool with a carbide insert can machine threads with a lathe. Before starting the cutting process, calculations for pitch, lead, depth, and major and minor diameters are essential. The tap handle method is commonly employed for tapping with a lathe machine, but it requires the workpiece to be securely clamped into the chuck.

Here&#;s a step-by-step guide for thread machining with a lathe:

If you are looking for more details, kindly visit threading in lathe machine.

1. Set the thread bit and adjust its height to align with the center point of the lathe. Ensure the tool bit is at the correct angle relative to the workpiece.


2. Gradually bring the threading tool closer to the workpiece.


3. Rotate the handle to generate threads. For instance, if aiming for threads with a pitch of 1 mm, the threading tool should move 1 mm as the workpiece completes one revolution.

Die-Cutting of Threads:

Die-cutting is a simple and cost-effective method suitable for mass production without requiring high precision. It involves using threading dies to create external threads compatible with internal thread counterparts.

Here&#;s an overview of the die-cutting process:

1. Chamfer the first end side of the workpiece at a 45-degree angle.


2. Choose an appropriate diameter for the die and secure it in a die-stock.


3. Position the dies on the end side of the workpiece and rotate the die-stock along its length to create threads.

Threading dies are commonly employed in metalworking and manufacturing to repair threads in worn-out holes or bolts. Threads produced with dies enhance strength and durability while reducing material costs due to minimal wastage.

Key Thread Design Tips: :

Design Tips for Designing Machined Threads

Uniform Surface Preparation:

• A uniform surface preparation is essential for ensuring the quality and functionality of machined threads.
• Before threading, it&#;s crucial to ensure that the surface of the workpiece is clean, free from debris, and properly deburred to prevent interference during threading.
• Any irregularities or imperfections on the surface can impact thread quality and lead to issues such as irritating or stripping.

Chamfering:

• A uniform surface preparation is essential for ensuring the quality and functionality of machined threads.
• Before threading, it&#;s crucial to ensure that the surface of the workpiece is clean, free from debris, and properly deburred to prevent interference during threading.
• Any irregularities or imperfections on the surface can impact thread quality and lead to issues such as irritating or stripping.

Thread Height and Thickness:

• The appropriate thread height and thickness are crucial for achieving the desired thread profile and functionality.
• The thread height refers to the length between the crest and the root of the thread, while the thread thickness is the width of the thread measured across the crest.
• These dimensions should be carefully calculated based on the thread pitch, diameter, and intended application to ensure optimal thread engagement, strength, and load-bearing capacity.

Surface Finishing for Threads:  

• Surface finishing is the final step in thread machining, enhancing both the threads&#; aesthetics and functionality.
• Black-oxide finishes and painting are two effective methods for surface treatment, offering corrosion resistance and aesthetic appeal.
• Black-oxide finishes provide additional protection against corrosion, making them particularly suitable for threaded components exposed to harsh environments or outdoor applications.
• Painting can further enhance the appearance of machined threads and provide additional protection against corrosion, abrasion, and wear.

Conclusion:

Mastering thread machining is essential for producing high-quality products in the manufacturing industry. By understanding the types of threads, key terminology, machining methods, design tips, and surface finishing techniques, manufacturers can ensure the reliability and durability of their products. For expert assistance in thread machining services, consult our experienced team of engineers specializing in all thread manufacturing aspects.

There are several screw thread machining methods in CNC. These different methods have their features and benefits. Here, we&#;d discuss the common ones and what makes them stand out.

1. Tapping

Tapping holes are ideal for use in producing internal threads. It is an economical as well as efficient threading method. This CNC method is applicable for use in threaded holes with the low accuracy of position as well as holes with a small diameter.

It as a method of screw thread machining has reduced CNC threading machine downtime. Also, the machining structure here is quite simple compared to other methods. Furthermore, tapping is a high-speed cutting process that greatly improves productivity and machining efficiency.

Cutting tools used in this machining method are cheaper, thereby reducing the cost of manufacturing. It is also a versatile process with a wide range of applications.

2. Thread Milling

This is another method used in making screw threads. This process utilizes a milling cutter as well as a 3-axis machining center. It also adopts a circular interpolation of the three main axes; x, y, and z linear feed. Thread milling is ideal for threading large parts or materials of high value.

Thread milling has a fast processing speed, high precision, and efficiency. The milling tool used often contains hard alloys. Also, milling cutter tools are versatile, reducing the need to acquire different tools for different milling processes. For instance, the same cutter can cut the left and right-hand thread using the same pitch of screws. You can adjust the hole diameters, tolerances, and material cut with minimal difficulty.

Threads made using milling have a superior-quality surface with zero burrs. This method is ideal for making thin-walled parts, machining blind holes, and asymmetric/ non-rotating parts.

3. CNC Threading on Lathes

Thread cutting on a lathe is another common screw threading process with a wide range of adoption. CNC lathes facilitate the production of high-quality screw threads. With this method, machinists can make several tapered threads, lead threads, and thread pitches.

Rigid tapping and single-point threading are two of the most common methods used in CNC lathe threading. Single-point threading uses a tool with an indexable insert with a shape and size that corresponds to that of the finished screw head.

4. Thread Grinding

This is ideal for use in threading hardened workpieces. Two main types of grinding wheels are used for this process; multi-line grinding wheels and single-line grinding wheels. The single-line grinding wheel has a pitch accuracy with grades 5 ~ 6. It also has a surface roughness of R1.25&#;0.08 μm.

Single-line grinding is ideal for making a precision screw, worm, thread gauge, shovel grinding hob, and small batch threading.

The multi-line grinding is divided into cut-in and longitudinal grinding methods. The major difference between these two methods is the width of the grinding wheel. In the longitudinal method, the width of the grinding wheel is less than the length of the thread being ground. On the other hand, the width of the grinding wheel used in the cut-in method has a greater length than the thread.

Are you interested in learning more about cnc lathe machining parts? Contact us today to secure an expert consultation!