Thread Machining: A Comprehensive Guide

As long as screws are still present in machined parts, thread machining remains an important aspect of metalwork. It facilitates the connection of parts at a low cost, making them ideal for use with fasteners, fittings, and connectors.

Aside from knowing what threads are, it is also important to identify the right type of thread for your project. So, what exactly does the term thread machining mean? what are the types of machining threads? Keep reading as we answer these questions and provide other important information about threading.

Types Of Threads

There are many types of threads according to different classification standards. For the Unified thread system, the UNF (fine) thread and UNC (coarse) thread are standard. However, the two major types of threads are internal and external threads.

       1) Internal Threads:

Internal threads, also known as female threads, are threaded features created inside a hole or recessed area of a workpiece. They are designed to receive mating fasteners such as bolts, screws, or threaded rods. Internal threads can be found in a wide range of applications, from assembling mechanical components to fastening objects securely.

So, when is an internal thread needed? You would require one if your workpiece needed screw insertions. Machinists use either hand taps or machine taps for cutting internal threads.

       2) External Threads:

External threads, also known as male threads, are machined on the outer surface of a cylindrical workpiece. They are designed to mate with internal threads of other components or to fit into threaded holes. External threads are widely used in fasteners, plumbing fittings, and other mechanical connections.

Using a lathe is one of the most effective ways of making external threads. Another method is to use a round die to cut the external thread by hand. The round die used in this case remains in a fixed die stock. Aside from round dies, there are also hexagonal square dies, ideal for interlocking use.

How To Do Thread Machining?

Thread machining typically involves the use of a cutting tool to remove material from a workpiece and create the desired thread profile. Here is a general step-by-step guide on how to do thread machining:

1. Select the appropriate cutting tool:

   Choose a cutting tool suitable for the thread type, pitch, and material of the workpiece. Common cutting tools for thread machining include taps for internal threads and dies for external threads. Ensure that the cutting tool matches the thread specifications and is in good condition.

2. Prepare the workpiece:

   Secure the workpiece in a suitable fixture, such as a vise or a lathe chuck, to prevent movement during the cutting process. Ensure the workpiece is properly aligned and centered to maintain thread accuracy.

3. Determine the starting point:

   Identify the starting point for the thread on the workpiece. This may involve marking the location or using a center punch to create a small indentation to guide the cutting tool.

4. Lubricate the workpiece:

   Apply a suitable cutting fluid or lubricant to the workpiece. This helps reduce friction, heat, and tool wear during the cutting process. The lubricant also aids chip evacuation and improves the surface finish of the thread.

5. Start cutting:

For internal threads (tapping):

• Align the tap with the starting point on the workpiece.
• Apply downward pressure while rotating the tap clockwise. Use a tap handle or a tapping machine to facilitate the rotation.
• Make sure the tap remains aligned and perpendicular to the workpiece to ensure the thread’s accuracy and prevent tap breakage.
• Cut the thread progressively by making several passes, retracting the tap periodically to break chips and clear debris.

For external threads (dies or thread-cutting tools):

• Position the die or thread-cutting tool on the workpiece, aligning it with the starting point.
• Apply pressure to the die or tool while rotating it in a clockwise direction.
• Maintain a steady cutting speed and feed rate to ensure consistent thread profile and avoid tool damage.
• Make multiple passes to achieve the desired thread depth and accuracy.

6. Check thread quality:

   Periodically inspect the thread during the cutting process to ensure it meets the desired specifications. Use thread gauges or other measuring tools to verify the pitch, diameter, and profile of the thread. Adjust the cutting process if necessary.

7. Clean the workpiece:

   Once the cutting process is complete, remove any chips or debris from the workpiece. This can be done using compressed air, a brush, or other suitable cleaning methods.

   Remember, the specific steps and techniques for cutting a thread may vary depending on the type of thread, cutting tool, and equipment used. It is essential to follow the manufacturer’s guidelines and best practices for the particular cutting tool and thread type to achieve accurate and high-quality threads.

At TDB Hanoi, external threads are made with a tapping machine and internal threads are created with lathe.

Thread machining is a challenge because of the need for skilled and professional equipment. If you want to make standard threads that stand the test of time, then TDB is the right company for you.

Who is TDB? We are a machining company from Vietnam with over 8 years of experience making parts that meet industry standards. With us, your threading project is in good hands as we have one-stop CNC machining services and advanced machines to attend to your order. 

CONTACT US TODAY FOR YOUR CNC MACHINING QUOTE TDB’s CNC Machining ensures consistent product quality. Your projects will benefit from increased production speed and efficiency. Request a free quote today to get started.