Thread Cutting and Forming: The Ultimate Guide to Machining Thread

Thread Cutting and Forming: The Ultimate Guide to Machining Thread

Threading is an important part of the metalworking process. For manufacturers, machining threads should never be taken for granted. There are now many different connectors and fittings available on the global market. Because of this, it is becoming increasingly difficult to find the right threads for your program.

There also seem to be some problems with the methods of cutting threads. Nonetheless, these methods are still the best way to make threads. To increase your profit margins, you should look into the various threading methods available. Read on to learn important facts about mechanical thread machining.

Table of Contents

What Are Machined Threads in Manufacturing?

Threads are continuously extending spiral ridges. The spiral ridge has the same portion on all four sides of a cylinder or cone. It can occur on the inside of a nut or on the outside of a screw or bolt.

The primary use of threads is to create a connection between two processes. When you think of a water bottle cap, threads come to mind. Together, the cap and the mouth of the bottle form a tight seal that prevents water from entering.

Movement is transferred from one object to another through the action of a coupling. Thus, the movement contributes to a mechanical advantage. These terms will help you better understand machining threads:

Crown: This is the surface where the two sides of the thread meet. When a thread protrudes from a cone or cylinder, it is called the crown. In other words, it is the top of the thread.

Side: The side of the thread connects the tip to the root. In theory, there is a straight line where the side surface intersects the plane of the shaft.

Root: The threaded surface that connects the side of another threaded shape is called the root. The part of the cone or cylinder right next to it is where the thread protrudes. In other words, it is the end of the thread.

Pitch: This is the space between two adjacent parallel areas on a thread. When you think about it, the pitch circle diameter is the theoretical diameter of a cone or cylinder.

Helix Angle: The helix angle is the number of turns the helix makes around the thread axis when the thread is flat. On the other hand, the helix angle of a tapered thread is formed by the conical helical region of the thread.

Machined Threads in Manufacturing

Types of Machining Threads

Different rules are used to classify threads into different categories. Spacer threads and machine threads are commonly used on hardware. On the other hand, the UNC (coarse) and UNF (fine) threads are the standard classification of the Unified Thread System.

We will discuss female and male threads in this paper.

Internal Threads

Internally machined threads are threads on a concave surface. Single lip threading tools are used to make these types of threads. This type of thread tap is used for certain internal threads. A tap is a metal tool used to create threads on the inside of a CNC machined part.

To fit a screw into a workpiece, an internal hole is required. For internal threads, you can use a hand tap or a machine tap to cut the threads. To cut internal threads, you need these things:

  • Twist drill
  • 900 countersink
  • Internal tap
  • Adjustable tap wrench (for hand taps)
  • Hand drill or box column drill (for machine taps)
  • Safety goggles

First, you need to find out how big a hole you need. Then, it is important to know which tap to use for the job. Standard sizes of taps for internal machining are used to separate them into different groups.

The following method can be used to calculate the tapping diameter:

Core hole diameter = Tap diameter – Thread pitch.

Centering with a punch is part of the thread-cutting process. The core hole is then drilled with a twist drill. 90-degree countersunk holes help to chamfer the stroke in the core hole. Place the tap in a tap wrench and turn it into the core hole. This cuts the threads.

Tapping of brass shaft parts on CNC lathes

External Threads

Threaded is another name for external threads. External threads are commonly used for screws, plug gauges, bolts, and nuts. Any part that can be turned can have external threads running through it.

Machining external threads with a lathe is very effective. They can also be cut by hand using round dies. In most cases, round dies are stored in a stationary die bank. As counterparts to internal threads, manufacturers usually use round dies.

Some molds are also hexagonal square molds. For interlocks, these types of molds work best. They help hold the housing in place and move the dies to hard-to-reach places. The following tools can help you cut male threads:

  • Round die and rod
  • File
  • Die stock
  • Vise (for clamping)
  • Flat-tip screwdriver
  • Cutting spray (for surface quality)

First, you need to file the edges of the rod. Then, you will chamfer the rod at 45 degrees. The chamfer should be slightly larger than the depth of the thread. After that, you can clamp the round die so that it stays in place. Cutting threads requires a lot of pressure on the round rod. Cutting sprays help to improve the surface quality of the part and make it last longer.

Types of threads machined in machining

How to Cut Machined Threads?

Thread cutting helps the part to form a threaded connection. Connections to complete screws require internal threads. Many connections also require matching male threads.

Knowing how to cut threads is an important skill for single-piece manufacturing. It is also needed for fixing things. This is because, for technical and economic reasons, machines are not always useful.

The following are the best methods for cutting machined threads:

Milling

This method uses a milling cutter that rotates. The shape of the milling cutter corresponds to the shape of the desired thread. Manufacturers use one or more cutters. All the cutting edges on a single cutter are in the same plane. Multiple cutters, on the other hand, have several rows of annular cutting teeth.

You can also cut threads with a hob. In this case, the cutter teeth will be arranged in a spiral pattern. Milling can create threads on the inside or outside. Threads cut with a milling machine have a very high degree of precision.

This method is most effective when the thread pitch is too large to use a mold. Many machinists consider milling to be better than lathe turning. Milling is the best method for machining parts such as screws. This is because milling makes parts quickly and correctly. In addition, milled parts can be finished with only one or two passes.

Turning Threads on a Lathe

Cutting threads on a lathe is another important threading process. Spiral ridges can be machined on the workpiece by this process. The spiral ridge on the part has a uniform cross-section. Multiple cuts using a threading kit is the method of machining threads on a lathe.

One of the most common methods of tapping on a lathe is using a tap handle. The machinist clamps the workpiece to the machine’s chuck. Then, for smaller and larger taps, a spring-loaded center or dead center is used. Both of these can be clamped to the tailstock.

The next step is to use a handle to turn the tap. The molded handle is another common method. It is perfect for cutting threads on the outside of the machine. Rigid tapping and single-point threading are two other methods of using a lathe.

Die Cutting

In most cases, die cutting is used to cut external threads. Parts can be manufactured quickly using die-cutting. Therefore, the cost of die-cutting threads is relatively low. The accuracy and quality of parts manufactured by this method are average. However, this method is good for most mass-produced products.

Generally, there are two different types of threading dies. They are:

  1. Bottom or round split dies: These dies can be used by hand. Of course, they can also be used in machines. They are round and have their radial cuts closed with screws. In this way, the fit can be changed to make it looser or tighter.
  2. Adjustable molds: In this case, two molds are built into a mold magazine. It is also possible to clamp the molds with a jig. With the tapered design, you can also move towards or away from the center. This allows for different degrees of fit. Adjustable dies are great for manual use.
Cutting machinery machining thread process

How to Design a Machined Thread?

To reap all the benefits, it is not enough to know how to cut threads. It is also important to know how to use the thread-cutting technique in the best possible way. Here are some design tips for using threads.

  • Female threads should have countersunk holes at the end
  • If there are no special requirements, lower-height threads are better than higher-height threads.
  • It is cheaper to use threads of conventional size and shape
  • At the beginning of the thread, there should be a flat surface aligned with the thread’s center axis
  • The wall of the tubular part should be thicker in order to withstand the pressure of molding or cutting
  • The end of the male thread of the part should be chamfered
Design a Machined Thread

Conclusion

To produce a high-quality part, you need to know everything about the manufacturing process. Cutting threads with machining processes is an important part of manufacturing parts. Although it may seem a bit difficult, you should not give up on it.

Instead, talk to someone who knows a lot about threading, Yonglihao Machinery has been in the business for more than two decades. Our engineers have been involved in a large number of CNC projects, so we can make sure you get the best service possible.

We always put our customers first and have a support team to make sure you get the right part for your needs. We offer the best threading services at prices that are hard to beat. If you have any questions, feel free to email us. You can also share your design files for an immediate quote!

FAQ

Thread machining is primarily used to help create threaded connections between parts. Using this method is one of the best ways to manufacture and fix single parts. It ensures better utilization of parts and simplifies the structure.

Yes. A milling machine can be used to machine threads. To perform thread cutting, you need a CNC machine center that can perform helical interpolation. This will ensure good thread cutting and accurate results.

When machining threads on a lathe, both internal and external threads can be machined. The choice depends on the purpose of the part.

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