Thread Machining Basics: Cutting Techniques and Process and Methods

Threading Machines are important manufacturing machines used to make threads on components. These threads are important because they help in fitting bolts, etc. Threading machines are used in everything from furniture to aerospace fields. This article will familiarise you with threading machining basics and how they are used in different applications.

What is Thread Machining?

This section is an introductory section related to threading machines:

Definition of thread machining in manufacturing

In manufacturing, threading machines are used to make grooves on the parts. These threads or grooves help withstand the tension and shear forces. Threading machines are used for screws to complex machinery parts, so these machines are of vital importance in the manufacturing industries. There are proper thread standards and specifications which are followed while metal threading etc.

What is the process of threading metal called and why it's essential for precision

The process of threading a metal is simply called as threading process. These internal or external threads on the parts are helpful for fastening or securing connections. If these threads are not precise, they will cause the loosening of connections and ultimately failures. That is why it is essential to make these threads with high precision.

Making Threads: Traditional vs Modern Methods

In ancient times or you can say before industrialization, there were manual tools which were used to make grooves over or within the holes of the parts. Due to manual work, there was low precision in making grooves and chances of human injuries were high. The following figure shows some ancient tools used for threading.

But after the innovation of the CNC machines, now these tools work automatically, significantly reducing the chances of error and human injuries.

Who invented threading and how has it evolved over time

Henry Maudslay invented the threading process, but then these tools were converted into a complex manual machine. Now this machine is automatic and works with high precision.

Thread-making methods from manual die cutting to CNC thread cutting

When innovation started, people tried to make their lives easier by innovating new products, materials, etc. The conversion from manual die cutting to CNC thread cutting was important to increase the production rate with high precision.

Thread Machining Design Considerations

The important factors are:

• Material properties
• Thread type
• Applications

Key Parameters for Thread Machining

When you do thread machining, keep the following parameters in mind:

• Pitch of the screw
• Thread size
• Standard thread angle

These parameters affect the mechanical properties of the parts.

Pitch of Screw, Thread size, and Standard Thread Angle

Pitch of the screw: Distance between the threads

Thread Size: The diameter of the threads

Thread Angle: flank-to-flank angle

Some standards are available for these parameters, for instance, the standard thread angle is 60ᵒ.

The relationship between thread pitch and thread strength

If these threads are tight, strength will be higher. When these threads are wide, resistance to shear force is increased.

Explanation of thread machining sizes and choosing the correct dimensions

It is important to create threads very precisely according to the dimensions. If these thread sizes do not match the dimensions of holes etc. it will not fasten firmly and will result in failures.

3 Types of Threads in Machining

There are many types of threading with distinctive applications. But here, you will get familiar with the 3 common types of threads in machining:

Machine threads

You will have seen the threads on the bolts and screws, these threads are called machine threads. These threads help in fixing tightly into nuts or bolts etc. Machine threads result in longer time usages.

Internal Threads

These threads are made on the internal sides of the nuts to enhance the fixing of bolts, etc. They are not limited to nuts; you will also see them in applications like plumbing and machine parts. The types of internal threads include tapered and straight threads.

What is the process of making internal threads?

• Make holes using the drilling process
• Use the threading tools etc.

External Threads

As the name gives a clue, the threads are made over the surface of different parts. Common examples include bolts and screws. The types of external threads include metric and unified threads. You can find its applications in the automotive and machinery industry.

Threading Process: How Does it Work?

It is important to know how a threading process works to use it effectively. Factors like machines, materials etc. affect the applications of the threads.

What is threading in machining and its key applications

In machining, threading means you grooves on or within the surfaces of the parts as you can see in the following figure:

The applications are:

• Secure connections
• Tight fixing of the components
• Durability increases
• Enhanced structural integrity

Threading process in lathe machines and CNC machines

You directly cut the threads using a single-point tool in the lathe machines. Its precision is less and is used in normal applications.

Due to programming, work is automatic in CNC machines. The precision is higher, and less labour is required.

The difference between thread cutting and thread forming

The difference between thread cutting and thread forming is simple. In the thread cutting, you will cut/remove the material to form threads. You will displace the material means not remove to form threads.

Thread Cutting

• Make holes using drilling
• Select the appropriate tools
• Start the cutting

Thread Rolling vs Thread Machining

In thread rolling, you roll the material instead of cutting to make threads on the surface. Thread rolling results in less waste of the material and stronger threads. The disadvantage of this process is that it is not suitable for all kinds of materials.

In thread machining, you need to remove the material to make threads. The material is removed in the form of chips, so the material waste is higher.

Methods for Cutting Threads

The methods include tapping, turning, milling, tap drilling and grinding which are discussed in this section:

Tapping

This process is used to make helical grooves into the material, tap tools are used for tapping. It plays its role by providing secure connections.

Thread Turning

Suitable for making threads on the cylindrical shapes. CNC machines are the best option for turning to achieve high precision in mass production.

Thread Milling

Thread milling is done to form threads by removing the material through a milling cutter. It provides:

• A superior surface finish
• Internal and external threads
• Deep threads

Fanuc G-code is a thread milling program example.

Thread Grinding

If you need a very high level of precision like in the aerospace field where the safety standards are very high, use the thread grinding method. The grinding machine is used to make threads.

Comparison of Thread Machining Materials and Technical Difficulties

There are two important things in thread machining: the material on which threads must be formed and the threading tool in any method. Machining becomes very difficult when you need or choose hard materials like high-carbon steel. You can face issues of tool breaking and even human injuries.

Thread Cutting Tools: Taps, Dies, and More

As I have discussed earlier, thread machining tools are essential, and you should have an idea what is the best tap or die for the respective material. The appropriate selection results in saving money and time. It will increase the production rate as well.

What are taps and dies used for

For external threads, use dies and taps for the internal threads.

What is a starter tap

It is used before starting the main threading process, that's why it is called as starter tap. A starter is often used when the threads have to be made on the hard materials or when the alignment is required.

Common Threading Mistakes to Avoid

During metal threading, the following mistakes should be avoided:

• Inappropriate selection of thread machining tools
• Inappropriate selection of thread machining equipment
• Inappropriate selection of thread machining techniques
• Selecting the wrong materials

What is cross-threading?

Cross-threading means while in metal threading, the threads get mixed, or they do not align properly. This misalignment results in weak joints and ultimate failures.

How to prevent cross-threading during the machining process

There are some factors which need to be understood before starting the threading process on machine parts etc. to avoid cross-threading. These factors include:

• Do not push with extensive force while fixing a bolt in a nut etc.
• Practice the installation process, before fixing a critical joint
• Try to remain aligned

Thread Quality and Inspection

Quality and inspection are two interconnected terms. You must inspect properly to get the best quality products. The same is the case while thread machining. Quality and inspection procedures must be applied before, during, and after manufacturing. You should inspect the material before taking it into the thread machining, whether it is defective or not, etc., to avoid issues during manufacturing.

How to measure thread accuracy and ensure precision

There are proper labs or quality control engineers who overlook the quality of the threads. There are different tools and techniques which help in assessing the accuracy and ensure precision. Check the parameters like:

• The distance between the thread crests
• Diameter of the thread
• Thread angle

If these factors are clear, then the production is accurate and precise.

Tools and techniques used for measuring machined threads

As you know, the manufacturing industries have proper labs containing the required tools for measuring machined threads like:

• To find thread diameter, thread micrometre is used
• Optical comparator to inspect thread angles etc.

• For 3D thread profiles, you can use a coordinate measuring machine (CMM)

Some common techniques include:

1. Visual inspection: Errors in threads are often visible because they are made over the surface of the part.
2. To check the finish of the threads, like in the case of gears, surface roughness measurements are used.

Applications of Thread Machining

1. In the automotive industry, thread machining is used to make threads on the fasteners. These fasteners are used in engine blocks, suspension assemblies and transmission systems. The CNC thread machined parts provide enough strength for bearing load.
2. You will see the extensive use of metal threading in turbine blades, gears, fuselage fasteners etc. in the aerospace field. Material like Ti and Al alloys are thread machined using CNC machines.
3. In the electronics industry, thread-machined parts are used as connectors, screws and housings in electrical devices such as smartphones.

These threads are very important because they provide uniform stress distribution, enhanced strength and reusability. These threads are made according to proper threading standards and specifications.

Conclusion: Mastering Thread Machining

We will conclude this article by saying that the threads are important to make on the surface or within the holes. These threads provide enhanced strength, tight fixing of the parts means strong joints etc. There are different methods available to form threads like taping, grinding etc. Multiple threading tools are available to make threads and different inspection tools and techniques are used to keep the accuracy and precision of machine parts.

FAQs for Thread Machining

Is machining threads expensive?

It depends on many factors like chosen materials, methods etc. Hard materials like high-carbon steels are difficult to machine so the threads are expensive.

Factors influencing the cost of thread machining

The main factors are the type of the material, threading method, threading machine and thread inspection tools and techniques.

What is the difference between die and tap in thread cutting?

Die and tap, both are different threading tools with specific usage. A die is used for making threads on the outer surface while a tap is used for making threads within a hole of the machine parts.

How do you make threads in CNC machines?

Perform the following steps:

• Select the appropriate threading tool according to the material
• Fix your workpiece
• Feed the dimensions in the program of CNC software
• Start the threading process

Thread Casting vs Threading

In thread casting, the threads are made during the casting or moulding process. While in the thread, you make threads on the pre-machined components.