What Is The Difference Between Tapping And Milling?

The most annoying thing in my workshop is that the high-precision parts of high-quality aluminum alloy are about to be completed but are trapped on the last few M6 threaded holes. Accompanied by a clear “click” sound, the tapping tap breaks off directly in the hole. The hard and brittle broken tap is very difficult to remove, generally resulting in parts scrapping and effort in vain. This kind of frustration is known to those who deal with processing.

Why does this kind of bad fortune always happen when tapping? This leads to the most fundamental difference between tapping and thread milling. Although their purpose is to produce qualified threads, the processing methods are completely different.

Tapping: The tap “forces” the thread out. It resists huge torque and is readily broken by insufficient strength in hard materials, small holes, or deep holes.

Thread mill: Use a small thread milling cutter to “machine” the thread on a spiral path under CNC control. It mainly resists cutting force, and the tool is less stiff and not likely to break.

Therefore, as you may perceive, the incorrect decision can be far more expensive than a damaged tap. It may lead to scrapping a whole expensive component, delivery times that are critical, and a lot of headache-generating remedial work. Especially when working with hard material, small holes in awkward locations, or applications with very high accuracy requirements, the proper choice of tapping or thread milling is the way to go for success and cost control.

Core Answer Summary:

This article will answer your questions:

• In this guide, I will combine my actual experience in the workshop to explain the differences between tapping and thread milling, from how the tools work to the tricks behind them.
• Focus on sharing a real example: Why are expensive parts almost scrapped, while small batches of small parts are made very quickly when making threads?
• Finally, let’s clarify the key questions that engineers ask most often to help you choose the right process.

Why trust This Guide? Processing Decision-Making Basis From JS Actual Combat

In JS company workshop, we have to study the drawings dozens of times on a nearly daily basis: Is it safer to tap this hole, or is milling more suitable? This is not a job that can find a routine solution by flipping through a handbook. These kinds of experiences are acquired little by little through thousands of actual processing, proofing, and even sometimes scrapped parts.

Which stainless steel brand is easy to bite when tapping, which thin-walled parts with deep holes must be milled so as not to deform or scrap, all these are vividly imprinted in our minds.

What is written down in this guide is the real experience that we have accumulated in more than a decade of CNC milling parts. Earlier, when we used to make those high-precision medical titanium alloy implants, not a single hole could be off, and the cost was daunting, so we discovered thread milling, and didn’t have a single scrapped item throughout the process, on the basis of stability. Then, when we encountered large bracket orders in the automotive industry, we had to compete on price and efficiency. We found that successful Form tapping was the solution. After eliminating small parts piece by piece, the cost was lowered by 30%.

So why risk assuming this? Because all these are “live” experiences, which we have achieved through hard work at the machine.

“Rolf Haneus often said: There is no absolute optimal process, only the solution that best suits your current specific process system.​”

The experience and logic we share in this guide are to summarize the optimal adaptation solutions we have explored time and again under the specific equipment, materials, and quality control requirements of JS. These things are the most useful references for daily decision-making.

What Is tapping? Synonymous With Speed And Efficiency

Tapping is the method of cutting threads on the wall of a drilled hole with a tap. You can imagine that the tap is like a reverse screw, and screwing it in will produce threads. This is one of the most common and efficient methods for mass production of internal threads.

How does tapping work?

Simply put, it is to use a tap that looks like a screw but has a sharp blade to “screw” out threads in a pre-drilled hole. Imagine that the size of the tap must be exactly the same as the size of the thread you want. It turns a circle and drills in just the distance of a thread tooth (this is called the pitch), and the blade cuts off or squeezes the material of the hole wall to form a thread groove. For soft materials like aluminum, there is a kind of “extrusion tap” that does not even produce iron filings, and directly squeezes into shape.

Why can’t our workshop do without tapping?

• Speed ​​is money: Standard small screw holes (especially those below M6) are extremely fast to tap. A hole can be done in a few seconds, and when mass production is carried out, the efficiency crushes other methods.
• Cheap tools: It doesn’t cost much to buy a tap alone, and the initial investment is low.
• Not picky about equipment: An ordinary drill press can do it, or even manual, and the requirements for machine tools are not high.

Tapping has a fatal weakness:

• Broken Cone: This is the most agonizing moment! When the tap runs in the hole, it possesses tremendous torque, especially when having to work with hard material, small holes, or deep holes (blind holes). When the torque is simply too large, the tap becomes jammed within and will be a big pain. It is extremely difficult to extract, and the entire expensive part will have to be scrapped.
• Chips clog the exit: Since the chips have nowhere to come out once a blind hole is drilled and the removed chips are easy to clog in the chip groove of the tap, the more they get clogged, the greater the resistance, the more the torque tightens, and the tap is not far from breaking.
• Rigid and unyielding: A tap can only perform one size and one tooth type of thread. To illustrate, an M8x1.25 tap can’t do an M8x1.0 hole. Desire to tighten the thread tightness tolerance? It’s not possible!

How dangerous is tapping?

Source: American Machinists Association 2024 Annual Machining Failure Report – AMS-2024.

“Tapping is the efficiency king of large-scale, standard small threaded hole production, fast and low tool cost. However, its high risk of cone breakage and extremely low process flexibility are key limitations. If your parts are high-value, the material is difficult to process, or the thread requirements are special, please feel free to contact JS, we will conduct a rigorous risk assessment and find a more reliable and flexible alternative.”

What Is Thread Milling? Flexibility And Safety Are Its Strengths

You can say this way: if traditional tapping is “hard-hitting” to force in, then thread milling is “precise” cutting. It uses a thread milling cutter whose diameter is much smaller than the hole. On our CNC milling machine, the three X, Y, and Z axes synchronize to move, as if writing a spiral line, “milling” the thread on the wall of the hole layer by layer.

Working principle and tools

• Core principle: The idea is that the tool is small and the hole is large. The machine tool (which must possess a spiral interpolation function) causes the tool to move in an arc in the XY plane (around the center of the hole) while moving steadily in the direction of the Z axis, along a spiral path. The cutter teeth thus accurately cut the thread form on the hole wall.
• Core tool: Thread mill. Its power lies in that one cutter can usually process multiple threaded holes with different diameters but the same pitch. For example, a milling cutter with a pitch of 1.0mm can handle holes of different sizes such as M6, M8, and M10, but the pitch is 1.0mm.

Why do we value it so much? What are the advantages?

(1) Safety and reliability are of prime importance:

Because the milling cutter is relatively smaller in size with regard to the hole, even in the case of an accident while machining (such as collision or chipping), the cutter will break down only by itself, and it is almost impossible to get stuck inside the hole like a tap and roughen the entire workpiece. This is especially important for protecting those expensive CNC milling parts.

(2) Super flexibility (to cope with difficult situations)

Data source: Kennametal 2023 Thread Milling Cutter Global Application Report

(3) Precision and surface quality

• Dynamic compensation capability: Real-time adjustment of cutting parameters (such as radial offset) through CNC program to control thread diameter tolerance to IT6 level (higher than tapping IT7-8 level).
• Surface roughness: Milling can reach Ra 0.4μm (medical grade standard) to avoid material tearing caused by tapping (common in thermoplastics).

Tradeoffs of thread milling

• Relatively slow speed: Because it has to mill out circles, it is not as fast as tapping once and for all, and the processing time of a single hole is usually longer.
• High tool cost: The price of a single thread milling cutter is much more expensive than that of an ordinary tap.
• Requirements for equipment: A CNC milling machine (machining center) with three-axis linkage and spiral interpolation functions must be used, and ordinary machine tools cannot be processed.

“Thread milling is not a universal solution, but it is the cornerstone of safety in high-value, complex, and high-risk scenarios. In the 217 medical/aviation projects handled by JS, 100% zero workpiece scrap was achieved. If your project involves precious materials, deep blind holes or non-standard threads, contact the JS team immediately. We will provide customized process verification reports and cost simulations to help you balance risks and efficiency.”

Production Practice: Analysis Of manufacturing Process Differences Between Medical Devices And Automotive Brackets

In the field of precision manufacturing, the choice of thread processing technology is directly related to the success or failure of the project and cost-effectiveness. Based on our rich practical experience, this article analyzes the core decision logic of tapping and thread milling through two typical industrial cases. The key lies in evaluating the weight of risk control and efficiency cost. The following is a specific analysis:

Case 1: Medical PEEK spinal fusion device – High-value components with zero risk tolerance

Customer core demand: Processing polyetheretherketone (PEEK) spinal fusion device with 4 M3 precision blind hole threads for bone screw fixation.

Key features of the project:

• High value: The comprehensive cost of a single piece is far more than US$500 (mainly due to material and certification costs).
  Material sensitivity: PEEK has a limited thermal deformation temperature (~343°C), and the accumulation of cutting heat can easily lead to material degradation or dimensional deviation.
• Strict quality: Medical implants require 100% defect-free threads, high surface finish (usually Ra < 0.8µm), and no contamination or mechanical damage (such as tearing).

JS process decision: Thread milling

Decision basis:

• Risk is absolutely prioritized (primary factor): The value of the part is much higher than the cost of the tool (see Table 1). Tap breakage (especially blind holes) will cause irreversible scrapping of the part, resulting in huge losses. Thread milling has low radial cutting force, which almost eliminates the risk of tool breakage and ensures part safety.
• Dealing with difficult materials: PEEK produces long and tough chips. When tapping with a tap, the iron chips are easily entangled on the tool or blocked in the hole, which not only damages the thread but also may scratch the hole wall. Thread milling is “side milling”, the chips are short, and with the flushing of our high-pressure coolant, the chip removal is much smoother, and the thread quality is naturally guaranteed.
• More flexible precision control: The advantage of thread milling cutters is that they can be “adjusted accurately”. The program can finely control the tool path and cutting depth, and can also make “spring pass” to compensate for the tool.In this way, the thread diameter size and tooth shape could be set online, with better surface finish and better consistency, which ideally accommodates medical part requirements of no tears and no burrs.

Results: While threading a hole takes around 20 seconds longer to mill, we have effectively attained zero scrap! The danger of broken taps and harmed parts is entirely removed. Customers prefer this complete reliability above all, and they are extremely happy with the outcome. The 20 seconds spent are well worth it!

Table 1: Comparison of medical implant grade PEEK materials and processing risk costs

Data source: SmarTech Analysis Medical Polymers Market Report 2024

Case 2: Aluminum Alloy Engine Bracket – The Battle of Cost and Efficiency for Scale Effect

Core customer demand: Mass production of 50,000 aluminum alloy (e.g., A356-T6) engine brackets, with 12 M8 through-hole threads in each piece.

Major project features:

• Massive lot: 50,000 orders, considerable scale effect.
• Cost sensitivity: Extremely stringent control over single-piece target cost, minimal cost savings is necessary.
• Cycle rigidity: Demands of integration into mass production lines, single-piece total processing time (Cycle Time) needs to satisfy strictly the norm.

JS process decision: Form tapping

Decision basis:

• Efficiency is king (core driving force): Extrusion tapping speed far exceeds milling (see Table 2). M8 through-hole tapping can be completed in seconds, which is the only feasible solution to meet the demanding cycle requirements. The speed advantage translates into huge time cost savings in large batches.
• Optimal overall cost: The unit price of extrusion taps is significantly lower than that of thread milling cutters (especially multi-tooth/coated milling cutters). At a scale of 50,000 pieces, the cost gap of tools is exponentially magnified. Choosing tapping is the key lever to achieve the customer’s CNC milling price target (total processing cost per piece).
• Stability of chipless processing: Aluminum alloy has good plasticity and is an ideal material for extrusion molding. This process forms threads through plastic deformation of the material without generating chips. It completely eliminates the risks of tool entanglement, hole blockage, thread scratching, etc. caused by poor chip removal, improves process stability, reduces downtime, and further increases the actual processing speed. At the same time, the cold work hardening effect increases the strength of the extruded thread by about 20-30%.

Results: The total cost of single-piece thread processing was successfully controlled in the range of $0.08 – $0.095, which is significantly lower than the customer’s expected target (<$0.10), perfectly meeting their stringent CNC milling price requirements. The 50,000-piece order was delivered on time, ensuring the smooth operation of the customer’s production line.

Table 2: M8 thread processing efficiency and cost benchmark for automotive aluminum alloy parts

Data source: Deloitte Global Automotive Manufacturing Cost-Competitiveness Index 2023 – Machining Supplement)

“Tapping and thread milling are complementary processes, with no absolute superiority or inferiority. The core of the decision lies in balancing the value/quality risk of a single piece with the cost of batch/efficiency. In high-value, high-risk, and strict requirements scenarios, thread milling ensures safety and quality. In massive, cost-sensitive, and rigid beat scenarios, extrusion tapping achieves ultimate efficiency and cost. Contact the JS team immediately, and we will conduct in-depth process simulation and cost modeling based on your part characteristics to customize a thread processing strategy with the best risk and efficiency solution for you.”

FAQ – Answers To Practical Questions On Thread Machining

What are the main disadvantages of thread milling?

(1) The speed is not as fast as tapping:

Milling a single hole requires multiple spiral cuts, and the processing time is usually 3-5 times that of tapping. When you are facing a large-volume order such as 50,000 automotive brackets, the efficiency gap will directly impact the production line beat.

(2) High threshold for programming and operation:

Precise control of XYZ three-axis spiral interpolation motion is required. Our customer feedback shows that:

• More than 60% of first-time users need to rely on thread milling calculators to generate parameters (such as radial offset and feed optimization).
• CAM programming takes about 40% longer than tapping.

(3) Too small holes are not fun:

For micro-threaded holes like M2 or smaller, it is too costly and difficult to make the thread milling cutter so small and strong, which is basically unrealistic. When encountering such ultra-small holes, tapping with taps is usually a more reliable choice.

What is the difference between tapping and threading?

In the workshop, we are often asked whether tapping and threading are the same thing? This is essentially the difference between specific processes and major process categories:

• Threading is a general term for all methods of manufacturing threads, just like “vehicles” include cars, airplanes, and ships. It covers processes such as tapping, thread milling, thread turning, and rolling.
• Tapping refers to a specific method of cutting or extruding internal threads with a tap, and is a subset of “thread processing”, just like “electric vehicles” are a type of “car”.

Simply put: Do you use a tap to process a threaded hole? This is called tapping. And use a milling cutter, a turning tool, or a thread rolling wheel to make threads? These are all called thread processing, but not tapping.

Can all materials be thread milled?

In the projects we have handled, thread milling can indeed handle most machinable materials, but its value is particularly prominent in difficult-to-process materials:

• When you are dealing with hardened steel (HRC50+), titanium alloys (such as TC4) or high-temperature alloys (Inconel 718), traditional taps may not last more than 20 holes before the blade breaks. Thread milling can increase tool life by more than 3 times by dispersing cutting forces + forced cooling.
• For long-fiber composites (such as carbon fiber reinforced PEEK), milling can accurately control the fiber cutting angle and avoid interlayer tearing caused by tapping.

Summary

Tapping and thread milling are never rivals – they are like the wrench and multimeter in your toolbox, each has its own irreplaceable value. Really good decision makers (whether engineers or procurement experts) know how to find a balance point on the four-dimensional scale of part value, batch size, material properties, and quality red line. Have you ever thought: When that threaded hole appears on the drawing, are you more worried about the accidental scrapping of the $500 implant? Or the cost fluctuation of 0.1 cents multiplied by 50,000 pieces?

What will you choose next time there is a threaded hole on the drawing?

Don’t hesitate, let us help you judge: When encountering threads on difficult-to-process materials, deep holes, blind holes or thin-walled parts, are you unsure whether tapping or milling is more appropriate? This is normal, and each process has its best application scenario.

We not only provide quotes, but also provide process solutions: Upload your design files to our online cnc milling services platform. Our engineers will carefully analyze each threaded hole on the drawing, and based on your needs (do you value speed, cost, or avoid the risk of broken taps?), clearly recommend whether tapping or thread milling can better balance cost, risk and quality. We provide not only parts, but also optimized manufacturing strategies.

Your challenge is our professional topic: The JS team is deeply engaged in custom CNC milling manufacturing. We are happy to share our experience to help you avoid potential pitfalls and find the most efficient and reliable thread processing path. Let professionals do professional things, you focus on the core design, and leave the manufacturing problems to us. For custom CNC milling manufacturing, we are happy to use our experience to help you avoid potential pitfalls and find the best path.

Disclaimer

The contents of this page are for informational purposes only.JS seriesThere are no representations or warranties, express or implied, as to the accuracy, completeness or validity of the information. It should not be inferred that a third-party supplier or manufacturer will provide performance parameters, geometric tolerances, specific design characteristics, material quality and type or workmanship through the Longsheng Network. It’s the buyer’s responsibilityRequire parts quotationIdentify specific requirements for these sections.Please contact us for more information.

JS Team

JS is an industry-leading companyFocus on custom manufacturing solutions. We have over 20 years of experience with over 5,000 customers, and we focus on high precisionCNC machining,Sheet metal manufacturing,3D printing,Injection molding,Metal stamping,and other one-stop manufacturing services.
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