Screw Thread Manufacturing Methods in Precision CNC Machining: 03 Most Popular Thread Processing

Precision CNC Machining is a revolution in screw threading manufacturing, this technique simplifies the process and reduces time and cost in production. CNC machining technologies have made screws more precise in custom desire. 

To understand and apply this tech in your project, you can contact us – TDB Tech anytime now. Explore screw thread manufacturing methods in CNC Machining and start applying them to your projects and tasks!

Now, TDB Tech will show you what they are and some benefits of these methods.

About Thread and Thread Cutting on CNC Lathe | Threading on CNC Machines

As we all know, threads are used to attach two separate parts. However, there is a fact that every thread has a matched pair of threads with their sex, including external threads as male, and internal threads as female. A CNC machine can cut a workpiece into separate internal and external threads.

Utilizing an indexable threading insert, single-point threading is the technique used to cut threads on CNC lathes. The threading process involves both cutting and forming, so the threading insert’s size and shape must match those of the finished thread. 

Single-point threading is a machining technique that produces helical grooves of a particular shape with uniform spindle advancement. The programmed feed rate in feed rate per change handles the thread’s uniformity. 

The leader of the thread, never the pitch, determines the threading feed rate. The lead and pitch are the same for single-start threads. The CNC system offers spindle synchronization for each threading pass because single-point threading is a multi-pass operation.

Hard materials that can be difficult to penetrate with a tapping tool are better suited for thread mills.

CNC lathes can also create high-quality single-point screw threads in a single setup of the CNC machined part. Without switching gears, CNC threading enables a wide range of thread pitches, tapered threads, and multiple lead threads. Utilizing a tool with a specialized threading indexable insert, whose size and shape should match those of the finished screw thread, is known as single-point threading.

What are the main parameters for indicating threads?

• Thread series: the variations of diameter and pitch in threads, that are applied to specific thread diameters (such as UN and Metric).
• Thread type: there are various thread types within the thread series, including UNC and UNF for UN, or M and MJ for Metric.
• Nominal diameter/major diameter/thread size: these denote thread size, referring to the thread’s main diameter.
• Pitch: the distance a point moves parallel to the axis in one revolution.
• Depth: how deeply a thread is cut (through or blind) into a hole.
• Allowances: tolerances that a thread fit may have.
• Class fit/tolerance/allowance: the major, minor, and pitch diameters, as well as whether a part is internally or externally threaded, are all within this tolerance range.

5 Common Types of Thread-Making Methods

In CNC Machining, there are numerous types of thread-making available nowadays. Here, let’s break down the various kinds of them. 

In general, thread cutting describes a method of creating threads on a workpiece, which uses forming tools or abrasive, Turning, Milling, and Grinding, for example.

The transmission chain of the machine tool makes sure that the turning tool, milling cutter, or grinding wheel moves a lead accurately and uniformly along the axial direction of the workpiece when turning, milling, and grinding threads. The tool (tap or die) rotates about the workpiece while tapping or threading, and the first formed thread groove directs the tool’s (or workpiece’s) axial movement.

Thread turning

Forming turning tool or thread comb tool using a lathe to make the thread. The most popular method of turning thread with forming turning tools is using a single piece and small batch production of threaded workpieces, which have a simple structure. 

Although thread comb cutters have high production efficiency, the structure of the cutter is complex. Therefore, it is only suitable for medium and large-scale production of short-thread workpieces with medium-turning fine teeth. The pitch accuracy of ordinary lathe-turning trapezoidal thread can only reach grades 8 ~ 9. Productivity or accuracy can be greatly increased when cutting threads on a specialized thread lathe.

Thread milling

Thread milling is processed by a thread milling machine with a disc or a comb milling cutter. 

While the disc milling cutter is mainly used for milling external trapezoidal threads on objects like screw rods and worms, the comb milling cutter is used for internal and external milling of conical and ordinary threads. 

As the thread is milled with a multi-edge milling cutter and the working part’s length is a bit more than the processed thread’s length, the workpiece can be processed only by rotating 1.25 ~ 1.5 revolutions, and the productivity is very high. 

Thread milling typically has a pitch accuracy of grade 8 to 9 and a surface roughness of R5 to 0.63 microns. This technique can be used for rough machining before grinding or for mass production of threaded workpieces with average accuracy.

Thread milling is another way for manufacturing screw threads on CNC machines by utilizing a milling cutter and a 3-axis machining center, adopting circular interpolation of the x-axis and y-axis, and linear feed in the z-axis, to move rotating cutting tools in a circular ramping motion.

The ability to cut a variety of threads and workpieces on the same machine makes thread milling particularly suitable for the thread processing of large parts and valuable materials. 

Thread grinding

Thread grinding is especially useful for creating precise threads on hardened workpieces. It can classify a single-line grinding wheel or a multi-line grinding wheel according to the cross-sectional shape of the grinding wheel.

Grinding wheel dressing is more convenient when the pitch accuracy of a single-line grinding wheel is grade 5-6, and the surface roughness is R1.250.08m. 

This technique works well for hobbing precision shovel screws, thread gauges, worms, and small batches of threaded workpieces. The two types of multi-line grinding wheel grinding are longitudinal grinding and cut-in grinding. 

In the longitudinal grinding method, the grinding wheel’s width is smaller than the thread’s length that needs to be ground. By repeatedly moving the grinding wheel longitudinally, the thread can be ground to the desired size. When using a cut-in grinding technique, the grinding wheel’s width is greater than the thread’s length that needs to be ground. 

The grinding wheel cuts into the surface of the workpiece thoroughly, after roughly 1.25 revolutions, the workpiece can be ground. Although the productivity is high, the precision is only a little lower, and the dressing of the grinding wheel is more challenging. Large quantities of taps can be shoveled and ground into threads for fastening using the cut-in grinding technique.

Thread tapping

Tapping is a typically efficient and economical threading method. Mostly, tapping is used to produce internal threads only. 

Because tapping covers most screw thread profiles and is applicable for threaded holes with small diameters and low positional accuracy. 

Rigid tapping, which relates to the rigid spring chuck holds the tap, and the spindle feed is consistent with the spindle speed under machine tool control, which is CNC machining’s fundamental configuration.

The accuracy of the tap or die determines the machining accuracy of tapping or threading. Although there are numerous methods for processing internal and external threads, only tap can process small-diameter internal threads. Tapping and threading can be done manually or with the aid of a lathe, drilling machine, tapping machine, and threading machine.

3 Benefits of Precision Threading on CNC Machining

High precision, high efficiency, and quick processing. 

Generally, the CNC cutting tool is manufactured with high precision using hard alloys. CNC machines are computer-controlled, which ensures that the threading process is repeatable and accurate. The machine can be programmed to follow a specific thread profile, which ensures that the threads are cut to the correct pitch and depth. This level of precision is not possible with manual threading methods.

Lower costs

In CNC machining, one tool can be used for both left and right-hand threads with the same screw pitch, as well as different thread tolerances, hole diameters, and a broad range of materials. 

Therefore, it can save as much as possible the tool inventory costs.

Moreover, CNC milling can easily change functions by removing chips and cooling; it also has better cutting than tapping. Specifically designed for CNC threading of difficult materials such as aluminum, copper, and stainless steel.

Thread milling is appropriate for CNC thread machining of blind holes with short bottom holes and holes that do not have a run-out groove. Thread milling produces smooth, burr-free surface finishes.

Flexible in Applications 

Precision threading on CNC machining is flexible in applications because of some reasons including:

• The CNC machine can be programmed to thread a wide variety of thread profiles, including metric, imperial, and custom threads
• The CNC machine can thread parts of different sizes and shapes, quickly and efficiently.

Here are some specific examples of how precision threading in CNC machining is used in a variety of applications:

• Automotive parts manufacturing: CNC threading is used to tap threads in engine blocks, cylinder heads, transmission housings, and other automotive components where high volume and precision are required.
• Aerospace parts manufacturing: The repeatability of CNC threading is essential for aerospace applications, such as jet engine components, landing gear, and avionics.
• Plumbing fittings and valves: CNC threading is used to produce high-quality threads in plumbing fittings and valves.
• Machine tools: CNC threading is used to produce the threads on machine tools, such as lathes, milling machines, and drill presses.
• Consumer goods: CNC threading is used to produce threads on a variety of consumer goods, such as furniture, appliances, and toys.

FAQs about Screw Thread Manufacturing Methods in CNC

How are screw threads manufactured?

Thread grinding is done on a grinding machine with specially dressed grinding wheels that match the thread shape. The process is typically used to create accurate threads or threads in hard materials; ball screw mechanisms are a common application.

What are the methods of cutting screw thread?

Taps and dies are the two most common thread-cutting tools. External threads are created by dies, while internal threads are created by taps. Threading or chasing refers to cutting external threads, whereas tapping refers to cutting internal threads.

What are the methods of thread manufacturing?

The following steps are involved in the production of cotton sewing thread: Opening, Cleaning, Carding, 1st Stage Drawing, Sliver Lap Forming, Ribbon Lap forming, Combing, 2nd Stage Drawing, Roving, Spinning, Clearing/Splicing & Winding, Assembly Winding, and Twisting.

What is the CNC code for threading?

G76 is the threading automatic cycle. 

Canned Cycles is the name given to these automatic cycles in CNC codes.

Summary

This article provided a review of all the types and benefits of thread cutting using a CNC Lathe. If you still want to learn more about machining operations from TDB’s experts, do not hesitate to contact us via

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