Methods for making threads - Threading tools guide | GSR Blog

Thread production: Methods for the production of threads

In this blog post we would like to introduce you to the different forms of thread production. Threads can, among other things:

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• • • milled
    • formed
    • drilled
    • rolled
    • shot
    • rolled and
    • swirled.

You wonder what the difference is, which method is better?

Machining and non-cutting method

There are different methods for the production of threads. Basically, the manufacturing methods can be divided into two sub-categories: Machining and non-cutting methods for thread production. For a better understanding a short overview follows.

Machining process

In the machining process, material is removed in the form of chips. This is also the reason for the name. The machining process can be carried out manually or mechanically. The tool is given a coarser surface by the removal.

(drilling, milling, turning and whirling)

Chipless process

Therefore, no chips are removed in the non-cutting process. The required thread profile is pressed into the tool. This results in a smooth surface and a higher thread strength. In the non-cutting process, the forming process is divided into hot and cold forming.

(forming, rolling and rolling)

Let us take a closer look at the three most common methods of thread production:

• • • • • 1. Drilling or cutting
          2. Milling
          3. Shapes or furrows

1. tapping and thread cutting

 

Tapping – also called thread cutting – is a cutting process. The material is removed by a step-like succession of the cutting edges.

✅ Advantages:

The field of application is very wide and the design of the tools is very simple. It can also be used for large workpieces with large diameters.

❎ Disadvantages:

With deeper threads there are problems with chip removal. There is the danger of cutting the thread.

 

2. thread milling

Thread milling is also a machining process. The thread milling cutter can mill an internal and external thread and can also be used on thin-walled workpieces. It is possible to produce the bore and thread in one working process. The thread milling cutter can be used on almost all materials.

✅ Advantages:

One thread milling cutter is required for different sizes. Only tools for left and right-hand threads are required. No problems with chips or tool breakage, as these can be easily removed. High cutting speed and feed.

❎ Disadvantages:

There are profile deviations with small thread profile angle and coarse pitch (e.g. trapezoidal thread).

3. Gewindeformen bzw. Gewindefurchen

Thread forming or thread grooving, on the other hand, is a chipless process. The thread profile is produced by displacing the material. The forming is carried out in a stepwise process. Due to the forming process, the thread has a higher thread strength and a better surface, as the material fibres are uninterrupted.

✅ Advantages:

No chip formation. Thread forming is suitable for greater thread depth. Longer tool life and cutting speeds. Cutting of the thread is excluded. A smoother and better surface structure is possible.

❎ Disadvantages:

Not applicable for all materials. Resharpening of the tool is not possible.

Conclusion:

Every production has its advantages and disadvantages. Which manufacturing method is preferred depends on the material, hardness and size.

 

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.

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:

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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:

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.

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