Thread Machining: Definition, Process Types and Application
Threads are an important and indispensable component in the intricate world of modern manufacturing. They facilitate connection between parts at a low cost and can be found everywhere from your mobile phone to an engine assembly. To produce high-quality, durable products we need to understand the nuances of thread cutting.
In modern manufacturing, managing multiple threads efficiently is crucial for optimizing production and ensuring high-quality outcomes.
In this article, we will discuss the intricacies of machining threads, exploring different types of threads, terminology, and the main machining technologies. We will also delve into the step-by-step machining process, applications of threads, and much more.
Let’s start from the beginning.
What Is Thread Machining In Part Manufacturing?
Thread machining is a vital subtractive process that involves removing material to create threads on a workpiece. Manufacturers use a range of machining tools to create various diameters of internal and external threads, often managing multiple threads simultaneously to enhance efficiency. As the threading tool rotates, it gradually takes out material forming a continuous helical ridge known as a screw thread.
The main purpose of a thread is to serve as a coupling agent between two components. It allows fastening through the interaction of the male and female thread.
A thread consists of several key parts. Let’s explore these elements in detail.
Main Parameters For Thread Profile
To design and effectively create a thread, you need to understand the key geometric parameters of the thread. They include;
Crest: As the name implies, the crest refers to the top point of a thread. It connects the flanks of the same thread and can either be flat or rounded.
Root: This is the bottom surface of the groove. It joins the flanks at the bottom of thread grooves.
Flank: Simply put, the flank is the side of a thread. It links the crest to the root and acts as a mating surface during assemblies.
Pitch: Thread pitch can be defined as the distance between a point on a threaded structure and an equivalent point on an adjacent thread. For example, the distance between the crests of two successive threads.
Thread Axis: It is an imaginary line that passes through the middle of a thread screw.
Major diameter: This refers to the diameter of the major cylinder, an imaginary cylinder (concentric to the thread axis) that binds the crests of an external thread or the roots of an internal thread.
Minor diameter: It is the diameter of the minor cylinder, which is an imaginary cylinder that touches the roots of an external thread or the crests of an internal thread.
Helix Angle: This is the angle between the thread axis and the helix on a straight thread. On a taper thread, the helix angle refers to the angle between the thread axis and the conical spiral of the thread.
Types Of Machining Threads
Threads fall under different categories depending on the classification standard. For example, based on the Unified Threads Standard (UTS), screw threads are grouped into UNC (coarse threads) and UNF (fine threads). Other types of threads include square, taper, left-hand, right-hand, and acme threads
That being said, all machining threads fall under two broad categories; external and internal threads.
Internal Threads
Internal threads, also known as female threads, run along the inside of a member. They are typically machined using taps, threading mills, or single-tip threading tools.
Internally threaded components such as nuts and tapped holes accept screws forming a solid connection within the workpiece.
External Threads
External threads, or male threads, are found on the outside surface of fasteners such as bolts, screws, studs, and plug gages. Most manufacturers prefer using a lathe for external thread machining. Alternatively, you can opt for die-cutting processes. External thread cutting is overall easier than creating internal threads.
How To Cut a Machining Thread? Fixed Machining Parts?
There are different thread machining techniques, each following a distinct procedure. In this section, we’ll focus on the step-by-step process of creating threads through tapping.
When cutting machining threads, managing multiple threads simultaneously can significantly improve efficiency and reduce production time.
Drilling Holes
Before you start machining threads, you need to have an appropriate size hole in the workpiece. The hole is machined using a drilling bit in a process known as tap drilling. The size of the drilled hole is based on factors such as the type and size of the tap and the required threads.
Thread Tapping
Once the tap drilling process is complete, you can now apply threads to the hole. This starts with carefully aligning the tap with the hole. The tap should be perpendicular to the hole to create perfectly straight threads.
After the setup, the tap is rotated clockwise under steady pressure. This motion gradually cuts threads into the workpiece. It’s necessary to reverse the direction of the tap after a couple of turns. This step breaks the chips and prevents tap damage.
Cleaning
When you’ve achieved your desired thread depth, clean the hole to remove any leftover debris and lubricant residues. Common cleanup tools include hand-operated air guns and specialized hole cleaners.
Testing
Inspecting and measuring the cut thread are the final essential steps of the thread machining process. A thread gauge can help you verify the accuracy of the created threads.
Common Screw Thread Machining Methods In CNC Process
Thread cutting is an essential process that generates screw threads, a component with a wide range of applications. There are different thread machining methods, each with its own strengths and weaknesses. In CNC machining, the ability to create and control multiple threads simultaneously can greatly enhance production efficiency and precision. Below, we’ll discuss the features of the most common methods of cutting threads.
Tapping
Tapping is a common thread-cutting method that creates internal threads in pre-drilled holes. This is accomplished using special tools known as taps. Tapping holes is efficient and economical, especially when machining smaller threads. You need to choose the right tap for your project to optimize performance.
There are multiple types of taps, each designed for a specific threading job. For example, a hand tap is operated manually with a tap wrench while a machine tap will cut threads with a drilling machine. Other types of taps include master taps, machine screw taps, spiral fluted taps, and fluteless taps.
Taps are typically made from high-speed steel (HSS). However, tough applications – such as threading a hole in a hard metal – demand a stronger tap material like solid carbide.
Thread Milling
Thread milling utilizes a rotating milling cutter to create threads. Manufacturers often prefer this threading method for its speed, accuracy, versatility, and high-quality finishes. It allows for fast turnaround times and does not leave burrs on the workpiece surface. In fact, machine shops can typically achieve the desired finish with just the first pass or two passes at most. Thanks to its remarkable efficiency, thread milling is ideal for fabricating parts such as lead screws.
The cutting tool’s shape matches the desired geometry of the threads. There are two main types of milling cutters, single-point and multipoint tools. As the name suggests, a single-point cutter only has one cutting edge that interacts with the workpiece during machining in a single pass. On the other hand, multipoint cutters utilize multiple edges during the thread-cutting process. Thread milling is suitable for both internal and external threads.
CNC Threading on Lathes
Another popular threading technique involves cutting threads on a metal lathe. This machining process can be used for both external and internal threading. It leverages the accuracy of CNC machines to create highly precise threads and achieve tight tolerances.
CNC lathes typically use a single-point tool with indexable threading inserts. Therefore, the insert can be switched to match the required thread contour. The ideal threading tool will vary from application to application, based on factors such as thread type, material, and size of the workpiece. High-speed steel (HSS) tools are suitable for soft materials while hard metals usually require carbide tools. CNC lathes also rely on different types of G-code for thread cutting.
Thread Grinding
Thread grinding is one of the most precise techniques for cutting threads. It uses a rotating grinding wheel to create threads into a bolt, screw, or other threaded component. This method is perfect for tough materials that are otherwise hard to machine. It delivers exceptional dimensional accuracy and an overall better surface finish. Thread grinding is often automated by using CNC equipment to control the movement of the grinding wheel.
You’re likely to come across two types of grinding wheels; single-line and multi-line grinding wheels. The former uses a single cutting edge and is suitable for precision screws, thread gauges, and low-volume threading. Multi-line grinding wheels are more productive since they remove more material during each pass. They are, therefore, ideal for higher-volume production.
Application of threading
Threads play a crucial role in a wide range of industries, each relying on them for different applications. Let’s explore some of the common threading applications across various sectors.
Automotive Industry
The automotive industry is heavily reliant on complex assembly processes. Threads provide a strong and reliable connection in various automobile parts such as engines, brake systems, suspension components, transmission systems, and steering components.
Aerospace Industry
The aerospace industry demands high-strength, accurate, and reliable connections. Even the slightest error can be disastrous in this sector. Aircraft components such as engines, landing gear, hydraulic, and flight control systems utilize different types of threads that offer safety and functionality.
Construction Industry
The construction industry is an essential part of a functioning society. Buildings require various threaded components for strength and sturdiness. Also, engineers heavily rely on threaded connections when building infrastructure such as bridges and ports.
Electronics Industry
In today’s world, almost everyone owns a mobile phone. Other popular electronic gadgets include computers, TVs, fridges, and washing machines. Such household electronics have one thing in common. They depend on screws and fasteners for efficient assembly and functionality.
Plumbing Industry
Threaded connections are essential in the plumbing sector. For instance, threaded pipes are widely used in residential, commercial, and industrial plumbing. They allow for watertight connections that prevent leaks and facilitate smooth water flow.
What is the difference between rolling and machining threads?
Thread rolling and thread machining are the most commonly used thread production techniques.
Thread machining, also known as thread cutting, is a subtractive process that involves removing material to create the desired thread profile. This can be done using cutting tools such as taps, threaded mills, grinding wheels, and threaded dies. Cut threads are cost-effective and highly versatile.
Thread rolling does not require any cutting or material removal. Instead, the workpiece material is displaced and molded into the required form using flat plates, round dies, and other forming tools. Rolled threads are known for their high quality and strength.
Author
Gavin Leo is a technical writer at Aria with 8 years of experience in Engineering, He proficient in machining characteristics and surface finish process of various materials. and participated in the development of more than 100complex injection molding and CNC machining projects. He is passionate about sharing his knowledge and experience.