CNC Tapping: An Introduction to the Process and Its Benefits

How Does CNC Tapping Process Work?

Tapping can only be performed in a pre-created hole. Therefore, a drilling operation is required to make the hole in the part. After the holes have been drilled, the parts are ready for tapping. The following will explain how the tapping process works.

Step 1: Choose Appropriate Taps 

Before you begin tapping, you must first pick the suitable taps. The taps must be chosen properly to make the thread as precise as possible. When selecting tap drills, you should consider numerous factors, including the screw size, diameter, threads per inch, material, and fit. A right-tapping tool is very important to the success of the tapping process.

Step 2: Carry out the Tapping Process

After choosing the taps, it is time to begin the tapping process. An automated feeding system normally feeds the part during a CNC tapping operation. Before the operation, the operator should set the CNC machining center to the appropriate speed and ensure the tapping tool is set to the needed depth. The tapping process can begin after the machining center’s settings have been completed.

The turning center may rotate the parts throughout the process. It is advised that the process be performed with a reasonably slow spindle speed. A speed range of forty to sixty rpm is preferable. The computer controls this entire process, and the system will notify you when the tapping operation is completed. The thread inside the holes is formed after tapping. Chamfering is thus required to remove the rough edges of the hole.

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.

Types of Taps in CNC Tapping

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 

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.

Spiral Flute Taps 

Spiral flute taps also have spiraled flutes for threading and chip removal. However, they have a flat end instead of a pointed end. The flat end provides more cutting edges, allowing for faster cutting and higher chip evacuation. Spiral flute taps are good for tapping through holes, blind holes, and tough materials where chip buildup is a concern. However, they require a pre-tapped starter hole to help guide the tap.

Form or Roll Taps

Form taps, or roll taps, are used for high-volume tapping operations. Instead of cutting threads like a conventional tap, form taps use hardened threads to displace material and form threads in a hole. This allows them to tap holes much faster while still producing high-quality threads. Holes tapped by form taps have a better surface finish and tighter dimensional accuracy. The rolling of the material eliminates cut chips and leaves an exposed grain flow around the thread. 

Types of CNC Tapping Process

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:

Through Hole Tapping 

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.

Blind Hole Tapping 

This type taps a hole that does not exit the other side of the workpiece. This requires chips to evacuate back out through the entrance hole, which can be difficult for larger taps. Gun nose or spiral flute taps are often used for blind hole tapping since they are better at evacuating chips. Peck tapping, which retracts the tap periodically to clear chips, may be required for deeper blind holes. 

Rigid Tapping 

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.

Floating Tapping 

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.

Synchronous or Self-reversing 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.  

Peck Tapping 

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  

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.

Advantages and Disadvantages of CNC Tapping

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

Advantages:

• High Productivity. CNC tapping allows for much faster threading speeds compared to manual tapping. This results in higher throughput and productivity.
• Consistent Quality. CNC tapping produces very consistent, high-quality internal threads with tight tolerances. It minimizes variability between parts.
• Low Scrap and Rework. The consistency and control of CNC tapping results in fewer scrapped or reworked parts due to tapping issues.
• Repeatability. Once CNC tapping programs have been created, the same tapping process can be easily repeated for other batches of parts.
• Versatility. CNC tapping can cut many thread types in different hole sizes and features. It handles most tapping needs.
• Safety. CNC tapping removes operators from the tapping process, reducing the potential for injuries like hand tapping injuries.

Disadvantages:

• Higher Initial Costs. CNC tapping requires a significant initial investment in CNC machines, tapping heads, cutting tools, and work-holding equipment.
• Complex Programming. Creating CNC programs for tapping operations can require substantial programming time, especially for complex parts. This additional programming adds cost.
• Higher Risk of Tap Breakage. The high spindle speeds and feed forces involved with CNC tapping can increase the chance of tap breakage, particularly when starting holes. This may damage parts and require tool replacement.
• Limited to Machined Holes. CNC tapping requires holes to be pre-machined before tapping. It does not replace the need for drilling holes before tapping.
• Difficult Setup. Setting up jobs for CNC tapping can involve precisely aligning and securing workpieces and selecting proper cutting tools. This setup time reduces productivity, especially for new jobs.
• Less Flexible. Once CNC machines have been programmed for a tapping cycle, modifying them on the fly cannot be easy. Manual tapping may have a faster changeover between different jobs. 

Common Applications for CNC Tapping

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.

1. Automotive Parts Manufacturing. CNC tapping is extensively used to tap threads in engine blocks, cylinder heads, transmission housings, and other automotive components where high volume and precision are required.
2. Aerospace Parts Manufacturing. CNC tapping produces the tight-tolerance threads needed for aircraft structures, jet engine components, landing gear, and avionics. The repeatability of CNC tapping is essential for aerospace applications.
3. Medical Device Manufacturing. Everything from surgical instruments to prosthetics to MRI machines relies on CNC tapping to produce the fine, precise threads needed for medical equipment. 
4. Electronics and Telecommunications Equipment. CNC tapping is used to reliably tap minute threads in electronic components and enclosures requiring high precision.
5. Plumbing Fittings and Valves. The high productivity of CNC tapping suits it well for tapping large quantities of threads in plumbing parts like pipe fittings, sprinkler heads, and valve bodies.  
6. Mold and Die Components. Intricately machined tools like injection molds, stamping, and forging dies commonly use CNC tapping to accurately thread ejector pins, core bolts, and other fitted parts.  
7. Oil and Gas Industry Parts. Oil and gas extraction and refining equipment utilize CNC tapping to tap piping, valves, pumps, meters, and other heavily threaded components.
8. Optics. Precision optics like telescopes, microscopes, lasers, and prisms use CNC tapping to tap their lens mounts, casings, and adjustment mechanisms where micron-level accuracy is necessary.
9. Pneumatic and Hydraulic Cylinders. The threaded ends and attachment points of pneumatic and hydraulic cylinders are commonly machined using CNC tapping due to the large number of cylinders produced. 

Difference Between Tapping and Threading

Tapping and threading are two methods for producing screw threads, but there are some key differences between them:

Tapping:

• 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 produce slightly weaker threads due to material lost during cutting. Although still quite strong for most applications.
• Requires frequent replacement or resharpening of worn-out taps. The cutting edges of taps dull over time and with use. 

Threading:

• Uses die to physically form threads onto cylindrical surfaces like bolts, studs, or rods. Dies are wrapped around the surface and squeezed to imprint threads.
• Produces external threads onto shafts. The threads are formed on the outer diameter of the workpiece.
• Creates threads through the displacement of material rather than cutting. No chips are produced during threading. Material is moved to form the threads.
• Typically a one- or two-step process: workpiece grinding/turning, then threading. No pre-drilling of holes is required. Just preparing the shaft surface.
• It can operate at much higher speeds than tapping since no cutting occurs. This results in higher production rates.
• Produces stronger threads because no material is removed. The full diameter of the shaft remains.
• Dies last much longer than taps since they are not cutting material. They eventually require resizing but not nearly as often as tap replacement.
• Usually requires a slightly oversized blank diameter to allow for material displacement. Extra stock must be left for threading.

Tapping cuts internal threads in holes while threading forms external threads on shafts. Tapping is usually slower and produces slightly weaker threads but with more precision. Threading operates faster and results in stronger threads but with slightly lower precision. The specific application requirements dictate which method, or combination of both, is most suitable.

The Tips to Achieve Optimal Results with CNC Tapping

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. 

Summary

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.

Knowing the CNC tapping process can ensure you get parts with high-quality, accurate threads. LEADRP is a company specializing in CNC machining and prototyping services. With rich manufacturing experience, we can provide solutions for various parts and threading. Contact us now for an instant quote!

Reference

What Is CNC Tapping? – From IMTS