CNC Tapping: An Introduction to the Process and Its Benefits

Tapping through CNC is a machining process and it helps to create threads within pre-drilled holes or nuts. It consists of insertion of a tap—a pointed tool at its tip—into an existing hole to create inside turning. This is considered an efficient, economical and very simple process especially when dealing with smaller threads. CNC tapping is a popular application used in aerospace, automotive, and medical device manufacturing for its precision and efficiency.

CNC tapping, which we will discuss in this article by explaining: what is CNC tapping? How does it work? Pros and cons Applications Difference between Tapping And Threading. Here you will read and discover all of CNC tapping.

In this article, we’ll explore the essentials of CNC tapping, including:
What is CNC tapping?
The Steps Involved in the CNC Tapping Process
Types of Taps in CNC Tapping
Types of CNC Tapping Process
Advantages and Disadvantages of CNC Tapping
Common Applications for CNC Tapping
Tapping vs Threading: The Difference

CNC tapping is one of the most common manufacturing processes that we use to create internal threads in parts. This means that internal threads are being formed in a drilled and chamfered hole to receive screws or bolts. Using computer numerical control (CNC) machines, tapping is performed with pre-programmed precision, ensuring efficient and accurate threading to meet exact specifications.
Tap is the cutting tool for tapping. It is wound into a hole and cuts the threads as it moves. You can select the appropriate one based on the type of hole you wish to thread. In general, hand taps and power taps are the two typical taps. Hand taps are the most common types, which include the taper tap, bottoming tap, and plug tap. For CNC applications or manual machining work, choose power taps, such as spiral point tap (gun nose or bull nose tap), spiral flute tap (gun), form or roll tap, and others.

Tapping can only be done for an existing hole. So the part needs an operation, which is a drilling operation to make the hole. Once the holes are drilled, everything is ready for tapping. Here’s the process on how tapping works:

Now before you can tap away, you need to select the right taps. Say that the thread has to be as accurate as possible, then you have to choose the taps properly. There are a myriad of factors that you need to account when choosing tap drills, such as screw size, or diameter, threads per inch (TPI), material and fit. The success of tapping is heavily dependent on a right-tapping tool.

Now that you have selected your taps, the next step is to start the process of tapping. A CNC tapping operation has the part generally fed via an automatic feeding system. The speed of the CNC machining center needs to be set before the operation, and the tapping tool depth also needs to be set prior to beginning. Once the settings on the machining center have been made, then tapping can start.

One example of this is in CNC tapping, where during the threading process the turning center may just be rotating the part. You should be working at one tricky spindle speed somewhere between 40 and 60 RPM, which is a good place to be for quality threads. The full operation is based on the CNC system, which operates precisely and alerts the user when failure to tap.

The threads are formed in the hole after tapping. Chamfering is used to clean up the edges around a hole, leaving a nice sharp edge devoid of burrs. This procedure makes certain that the opening is well prepared and clean for its intended purpose.

It should be noted that lubrication should always be used while drilling a hole and producing a thread in part. The oil prevents harsh sounds from being made by the parts. In addition, it can also smooth out the cuts. And the oil aids in removing tiny chips from the parts throughout the process. The oil also prevents overheating of the drill.

Selecting the proper tap type for each application is key to success in any CNC tapping operation. In some situations, it may take trial and error to determine the best approach based on the machine, holding tools, and properties of the parts being threaded. Three main types of taps are used for CNC tapping: spiral point taps, spiral flute taps, and form or roll taps.

Spiral point taps are the most commonly used taps for CNC tapping. They have a pointed end and two spiraled flutes that wrap around the tap to cut threads and evacuate chips. The pointed end allows the tap to self-start in a pre-drilled hole. Spiral point taps can be used for most applications except tapping through holes or into blind holes.

These taps have spiral flutes to assist in both threading and effective chip removal. Spiral point taps have a flat end instead of the pointed end of spiral point taps. This flat end, in turn, multiplies the number of cutting edges achievable and allows for effective clearance of chips while increasing speed while cutting.

These taps are especially good for threading in holes, blind holes as well as tough-to-machine materials where chip packing can be an issue. On the other hand, spiral flute taps will need a pre-tapped starter hole to prevent the tap from wandering during threading.

Form taps balanced for higher volume tapping operations, also called roll taps. Form taps use hardened threads that displace material to form threads in a hole instead of cutting them like a conventional tap. This enable them to thread holes at a much faster rates but still high quality threads. Form taps provide superior finish and better dimensional accuracy than form-less holes. Rolling the material removes cut chips and exposes a grain flow around the thread.

The CNC tapping process can be optimized by selecting the proper tapping type for a specific application’s hole features, material, and quality needs. There are several types of CNC tapping operations:

It taps a hole that goes completely through the workpiece. Through hole tapping allows chips to evacuate through the bottom of the hole. It typically produces the best thread quality since there is room for chips to escape. Spiral point and flute taps generally work well for through-hole tapping.

This type of tap is used for creating threads in a blind hole, which does not pass through to the other side of the workpiece. In such cases, chip evacuation can be challenging, especially when using larger taps, as the chips need to exit through the entrance of the hole.

Gun nose or spiral flute taps are commonly employed for blind hole tapping due to their superior ability to remove chips efficiently. For deeper blind holes, peck tapping is often necessary. This technique involves periodically retracting the tap during the process to clear chips and prevent clogging, ensuring smooth and precise threading.

The tap is rigidly held by the tool holder and tapping head, synchronizing the tap’s rotation and feed to match the spindle speed. No axial float is allowed. This provides the most accurate tap control and the highest risk of tap breakage if misaligned. It is best for shallow, through holes in softer materials.

The tap is allowed a small amount of axial float to follow the hole. This reduces the risk of tap breakage in misaligned holes or with workpiece movement during tapping. However, some loss of control and thread quality may result. The floating tapping handles medium to deep holes better than rigid tapping.

The tap rotation is reversed at the end of each cycle to back the tap out of the hole. This prevents the need to stop and reverse the spindle for tap retraction. It saves time but requires a tapping head to quickly reverse the tap without losing its feed synchronization. It is often used for high production tapping of through holes.  

The tap advances into the hole in short “pecks” and then fully retracts to clear chips before re-entering the hole. This is often used for blind hole tapping where chip evacuation is difficult. It helps prevent chip jamming but reduces productivity compared to continuous tapping.

Form tapping uses hardened taps that displace material to form threads rather than cutting them. It allows much faster tapping speeds and longer tool life but is only suited for certain materials. And it requires higher machine rigidity and torque.

CNC tapping is a critically enabling technology for fast, precise, low-cost manufacture. The advantages and disadvantages of CNC tapping are as follows:

Advantages:

1. High Productivity. Compared to manual tapping, CNC tapping is much faster when it comes to the threading speed of the process. This translates into improved throughput and higher productivity.
2. Consistent Quality. CNC tapping can create highly precise, high-quality internal threads with tight tolerances. Details: It reduces the variation between components.
3. Low Scrap and Rework. CNC tapping produces less scrapped or reworked parts due to controlled tapping.
4. Repeatability. After creating the CNC tapping programs, this tapping method can be repeated for other batches of components effortlessly.
5. Versatility. Different hole sizes and features can be tapped using many different thread types through CNC tapping. The default tap feature works for most cases.
6. Safety. Eliminating Operators in the Tapping Process Gear material machining creates dangerous or risky tapping processes like hand-tapping injuries that CNC tapping does not need human operators to go through.

Disadvantages：

1. Higher Initial Costs. The first is probably going to be the most important, CNC tapping has a high upfront cost of CNC machines, tapping heads, cutting tools and work-holding equipment.
2. Complex Programming. For complicated parts, significant programming time may be needed to CNC programs for tapping operations. This extra programming comes at a cost.
3. Higher Risk of Tap Breakage. CNC tapping involves high spindle speeds and feed forces, so it can break taps when you try to start holes. This damages portions and would need tool replacement.
4. Limited to Machined Holes. In CNC tapping, holes must be pre-machined prior to the process of tapping. However, it does not eliminate the need to drill holes before tapping.
5. Difficult Setup. When preparing jobs for CNC tapping, it can require very accurately aligning and securing workpieces along with selecting proper cutting tools. All of this takes time and cuts into productivity — for new jobs, even more so.
6. Less Flexible. Altering them on the fly is not terribly easy once cnc machines have been programmed for a tapping cycle. You can usually switch between jobs much faster if you are tapping manually.

CNC tapping is a broadly applied manufacturing process used in the automotive, aerospace, medical device, electronics, industrial equipment, and consumer goods industries, wherever internal threads must be machined to tight tolerances. Its speed, precision, and automation suit these industries.

That enables CNC tapping to be used extensively for thread production in parts that require high accuracy and high volume automotive machining but the number of options available can leave you confused.

CNC TAPPING → Tight-tolerance threads for aircraft structures, jet engine components, landing gear, and avionics. This is essential for aerospace applications where its repeatability matters.

Surgical instruments, prosthetics, MRI machines – CNC tapping creates the fine, exact threads that are needed for medical equipment.

NC tapping is used to have small threads in electronic components and enclosures, which are sensitive that requires high precision.

CNC tapping’s productive capabilities lend itself to tapping high volumes of threads in components such as pipe fittings, sprinkler heads and valve bodies.

Injection molds, stamping dies and forging dies are some of the many tools that require CNC tapping for more precise threading of ejector pins core bolts and other fitted parts.

CNC tapping is used for reliable threading of piping, valves, pumps, meters and other heavily threaded equipment in oil and gas.

Precision instruments such as telescopes, microscopes, lasers and prisms rely on CNC tapping to produce threaded lens mounts, casings, and adjustment mechanisms with micron making precision.

Because pneumatic and hydraulic cylinders have a high production volume, the threaded ends and attachment points are commonly machined using CNC tapping.

Tapping and threading are two methods for manufacturing screw threads, however there are some distinct differences:

It uses rotary cutting tools called taps to cut threads in holes. Taps are either manually turned or machine-driven (as in CNC tapping).

·Produces internal threads in holes. The tap cuts threads directly into the pre-drilled hole.

·Chips are produced and must be removed. Tapping cuts material away from the hole, which generates chips that must be evacuated.

·Usually employs a three-step process:  drilling, tapping, and chamfering. Holes are pre-drilled and then tapped. An optional chamfering step can deburr the thread entrance. 

·Tends to be slower than threading since it removes material. The cutting action limits how fast taps rotate and advance into the hole.

·It can create threads that are not as strong due to material lost during the cutting process. However, still very strong for most applications.

Needs tap replacement or resharpening of worn taps at regular intervals. As with cutting tools, the tap has cutting edges that become dull over time and use.

Die: physically forms threads on cylindrical surfaces such as bolts, studs and rods. A die envelops the surface and it will squeeze in threads to make an imprint.

Forms external threads on the shaft, that is, it creates a thread along a cross-section at the periphery of the workpiece.

Equivalent to material displacing, not cutting; threads are formed. The process used to create these threads is chipless since it displaces the material.

·Follows a one- or two-step process, starting with grinding or turning the workpiece, then threading. No pre-drilling of holes is needed; only the shaft surface needs preparation.

·Operates at higher speeds than tapping since no material is cut. This allows for increased production rates.

·With the internal removal of no material, full shaft diameter is preserved thus providing for stronger threads.

Dies have more life in them than does taps, because they don’t actually cut. It needs resizing now and again, but never replacing.

Needs larger blank diameter due to material displacement Some extra material is left in the stock for threading.

Tapping creates internal threads in holes, and threading makes external threads on shafts. Unlike in-bore tapping, which is slower and creates less robust threads but provides increased accuracy. Threading is a faster process and creates more robust threads however, with decreased accuracy. The decision on what method to use will depend on the needs of your application.

Here are some tips to achieve optimal results with CNC tapping:

1. Select the Proper Tap.Choose a tap specifically designed for the thread size, hole feature, and workpiece material. For tough materials, consider carbide taps. For high volumes, form taps can help.
2. Hold the Workpiece Securely.Rigidly clamp the workpiece in a vise or fixture to prevent movement during tapping. Use jigs or angle plates if tapping at an angle. Workpiece vibration will lead to poor thread quality or tap breakage.
3. Calculate Proper Spindle Speed. Spindle RPM must be high enough to tap holes efficiently but not so high as to weaken or overheat the tap. Use tap manufacturer recommendations based on tap size and material.  
4. Set Appropriate Feed Rate.The feed rate controls how fast the tap advances into the hole. It must be slow enough to allow chip evacuation and prevent tap overload. But too slow and productivity will suffer. Feeds and speeds work together.  
5. Provide Lubrication and Cooling. Tapping fluid or oil helps lubricate the tap, reduce heat, provide rust prevention, and evacuate chips. For blind holes, a tapping fluid pump can help force fluid into the hole. Use a water-soluble fluid for most materials. 
6. Peck Tapping for Blind Holes. Retract the tap fully from the hole periodically to clear chips rather than a single continuous cut. This helps prevent chip buildup in blind holes where evacuation is difficult. It reduces tap overload.
7. Follow Minimum Thread Depth Recommendations.Tap holes deeper than the minimum recommended depth based on the thread diameter when possible. Deeper threads have more engagement and are stronger. They also allow more margin for error if tapping slightly out of the perpendicular. 
8. Check Tapped Hole Thread Quality.Use go/no-go gauges to verify a percentage of tapped holes meet the proper thread size and acceptable tap limits. This catches potential issues before too many parts have been completed. 

CNC tapping creates internal threads on a workpiece using a rotating tool, typically a tap and a feed mechanism. The feed mechanism drives the tap into the workpiece while rotating it, creating threads as it moves. This process can be automated and controlled using computer numerical control (CNC) technology, allowing for improved accuracy and repeatability. CNC tapping is used extensively in high-volume production environments where repeatability and quality are essential.

Interested in incorporating CNC tapping into your production line? At Dongguan Great Light Metal Technology Co., Ltd., we specialize in CNC machining and custom threading solutions. Contact us today to discuss your project requirements.

Metals like aluminum, steel, and titanium are commonly tapped, along with some plastics for specialized applications.

Yes, CNC tapping excels in creating precise small threads, making it ideal for electronics and medical devices.

Using proper lubrication, selecting the right tap, and optimizing spindle speeds can minimize tap breakage.

Drilling and tapping are distinct actions. Drilling is making a smooth hole in a material using a drill and motor. Tapping is the action of creating a thread into the hole’s side.