EXPERT GUIDE ON THREADING TAPS

Tom Beaumont

Product Training Manager

18 years engineering experience, specialising in 3 & 4 axis CNC milling, turning and horizontal boring.

We will cover the basics of threading taps, the differences between machine, hand, and roll taps, the distinctions among spiral flute, spiral point, and straight flute taps, and the considerations for thread milling.

In this blog series, we'll provide valuable insights and practical advice on Threading Taps from myself an experienced engineer with 18 years of expertise. Whether you're a novice engineer looking to expand your knowledge or someone seeking a refresher in the field of threading, this guide is here to help you understand the intricacies of machine taps and their applications.

What is a Threading Tap?

The use of threading taps is crucial for creating accurate and precise screw threads. In this first section, we'll delve into the fundamentals and explore the question: What is a threading tap?

Understanding Threading Taps: A threading tap, commonly referred to as a tap, is a cutting tool used to create Internal threads within a pre-drilled hole. The tap consists of a cylindrical shank with four flats at the drive end and has flutes running the length of the cutting edges. The flutes are designed to aid chip flow and allow cutting fluids to reach the cutting edge. Taps have a lead chamfer/angle, also referred to as form B,C & E, these act as a guide when the tap enters the predrilled hole, they also help reduce cutting loads.

Function of Threading Taps: Threading taps serve the primary function of cutting internal threads in various materials, including steel, stainless steel, Inconel, titanium, aluminium, cast iron and plastic. They are indispensable tools in industries such as manufacturing, automotive and aerospace.

Selecting the Right Threading Tap: Choosing the appropriate threading tap is crucial for achieving accurate and reliable results. Factors such as material type, hole diameter, and thread specifications must be considered when selecting the tap. It's important to consult reference guides, tap charts, or seek advice from experienced engineers to ensure the right tap is chosen for the job at hand.

It is vitally important to choose the correct tap for your threading application. This is due to the fact that often, the tapping cycle is one of the last processes to be carried out when completing a job. Therefore, any issues that occur due to the incorrect tool being used could increase the risk of scrapping the entire job or a costly, time consuming process like spark erosion to remove the broken tap.

Machine vs Hand Taps vs Roll Taps

In this section, we'll compare three different types of taps: machine taps, hand taps, and roll taps. We'll discuss the reasons why and where you would use each type. By understanding their unique characteristics and applications, you'll be able to make informed decisions when selecting the appropriate tap for your specific projects.

Machine Taps: Machine taps, come in options of spiral point or spiral flute, are specifically designed for use with machine tools such as CNC lathes and Milling machines, drill presses, manual lathes and milling machines. Machine Taps are manufactured using special grinding processes that provide unique geometries with optimal flute space for improved chip evacuation, the unique geometries also make them suitable for high-speed operations. Our best performing general purpose machine tap is the Prime-X from YG-1, with 50% higher tapping speeds!

Hand Taps: Hand taps, also referred to as first, second taps and plug taps. They are a versatile tools commonly used for manual threading operations. They have straight flutes and a chamfer at the tip to aid in aligning the tap with the hole. Hand taps require more care and control compared to machine taps but offer flexibility and convenience in various situations.

Roll Taps: Roll taps, also known as thread-forming taps or cold-forming taps, are unique in their operation. Instead of cutting the material and creating swarf they reshape the existing material to form the thread. Roll taps have no flutes, however they are available with or without oil grooves. Oil grooves allow cutting fluid to pass through while the forming process takes place. When using roll taps specially calculated pre-tapping drill sizes are necessary.

Conclusion: Machine taps are ideal for high-volume, automated operations, while hand taps offer flexibility and precision in manual threading tasks. Roll taps excel in situations where material integrity and high-quality threads are paramount. Understanding the strengths and best uses of each tap type will empower you to make informed decisions when selecting the appropriate tool for your specific threading requirements.

Spiral Flute vs Spiral Point vs Straight Flute Taps

Now we'll explore the distinctions between spiral flute, spiral point, and straight flute taps. Each type has its own advantages and best-suited applications. By understanding the differences, you'll be able to choose the most suitable tap for your threading requirements, whether it's chip evacuation, specific hole types, or material considerations.

Spiral Flute Taps: Spiral flute taps, also known as helical flute taps, feature a spiral-shaped flute design that runs along the cutting length of the tap. The spiral flute geometry helps evacuate chips efficiently during the threading process of a blind hole, the spiral flute design draws swarf out of the hole like that of a twist drill. It is crucial that spiral flute taps are used when tapping blind holes to reduce the risk of tap breakage.

Spiral Point Taps: Spiral pointed taps are generally stronger than spiral flute taps due to their shallower flute design, giving them a stronger core. The flute geometry of a spiral pointed tap is designed to push swarf forward making them first choice for tapping through holes, this is where the tap can pass completely through the predrilled hole.

Straight Flute Taps: Straight flute taps have a straight flutes that run parallel to the tap's axis. These taps have a simple design without spirals or points. Straight flute taps are typically used for tapping short chipping materials such as cast iron and can be used in both blind and through holes.

When Should You Thread Mill Instead of Tap?

Thread milling is an alternative technique to tapping that offers unique advantages in certain situations. In this section, we'll discuss the scenarios where thread milling is preferred over tapping. Understanding when to use thread milling can broaden your options and improve efficiency in specific threading applications. When using a thread mill the operator has greater control over the process. Thread milling is a much safer and more consistent process for unmanned processes or expensive workpieces it is certainly the preferred method.

Hard to cut materials: If you're working with tough materials like hardened steel, Inconel, titanium, Thread milling is a good choice. When cutting more difficult materials thread mills really do come in to their own. The forces increase with taps leading to more breakages whilst with a thread mill you can control the number of passes to reduce cutting forces leading to a more consistent and higher quality thread.

Large Diameter Threads: When tapping holes above 20mm often some machine tools can struggle with the power required to drive the machine tap. Taps can become very costly at this size and thread milling should be seriously considered to not only reduce cost per hole but also reduce the chance of large tap breakages. Due to the very low cutting forces produced when thread milling they also greatly reduce the load on the machine compared to a tap.

Complex Thread Profiles: If you need to machine threads with a special or unusual form, then traditional tapping methods would not be an option. With thread milling, you have the flexibility to create custom thread profiles. This is particularly useful in industries like aerospace or automotive, where unique thread designs are common.

Threads with Interrupted cuts: When you're threading through or blind holes that have interruptions like a cross hole, thread milling is a good choice. Tapping such holes can lead to problems with chip build up and tap breakages. Thread milling speeds feeds and depths of cut can be adjusted to work around such features, ensuring consistent threads without the risk of chip build up or tool failure.

High Production Volume: If you're working on a large-scale production project, thread milling can be more efficient. With the right equipment and programming, thread milling can be automated and done at a faster rate than manual tapping. This saves time and increases productivity, making it beneficial for high-volume production.

Summary Of Thread Milling: Thread milling is often an overlooked process by some machine shops due to the fear of the unknown and the worry about difficulties programming the tool. It is a very simple process and software like Vargus Genuis make it remarkably easy due to it having the ability to select the correct tool for you and generate a working CNC program for your machine. You can use one tool to generate multiple threads as well as create a cleaner thread than taps, you end up with a much safer process due to it removing the fear of breaking a tap and scrapping the part.

Conclusion on an Expert Guide to Machine Taps

In this expert guide on machine taps, we have covered the basics of threading taps, the differences between machine taps, hand taps, and roll taps, the distinctions among spiral flute, spiral point, and straight flute taps, and the considerations for thread milling. By delving into these topics, we aim to equip you with the knowledge necessary to make informed decisions and achieve optimal results in your future engineering projects.

For more expert advice on selecting the right threading tap for your application please contact our technical team on 01924 869 615 or email sales@cutwel.net