Among the CNC machining services we provide, CNC milling and CNC drilling are the most common process requirements. However, there are still many people who do not know much about the two subtractive machining processes. Your in-depth comprehension of the distinctions between the two will actually help you optimize the machining process, and even improve the quality and market competitiveness of parts. Next, I will introduce the differences between them in detail.
What is CNC Milling?
As an important part of the subtractive process, CNC milling can realize precision CNC machining and manufacture various complex-shaped precision parts by rotating cutting tools. During the milling process, manufacturing precision parts of various complex shapes by rotating cutting tools. During the milling process, the machine tool follows the instructions (G code and M code) entered by the operator to control the tool along the X, Y and Z axes to cut the workpiece, remove excess material, and gradually form the required parts.
In addition, milling supports the processing of a variety of materials, including metal and plastic. It can be said that any complex part machining task you want can be easily accomplished.
What is CNC Drilling?
CNC drilling is a process that uses a two-point rotating tool to perform cutting along the axial direction of the workpiece. This process mainly uses advanced CNC systems and servo drive technology to control machine tools to achieve precision machining, and uses the drill bit to automatically move along a preset trajectory to complete drilling operations on the workpiece.
CNC drilling can accurately control the depth and diameter of the hole, reducing human intervention and significantly increasing work efficiency.
What is The Difference Between Milling and Drilling?
After introducing the definitions of the two processes, I will introduce to you the differences between CNC milling and CNC drilling in detail.
CNC Milling vs. Drilling: Cutting Technique
First of all, the biggest difference between the two is the cutting process. CNC milling mainly uses cutting tools such as milling cutters to process fixed workpieces. During the process, the tool can rotate and act transversely on the workpiece surface, while the workpiece itself can also move. In other words, the feed direction of the tool can be at any angle with the tool axis, allowing the processing of various complex shapes to be completed.
On the contrary, CNC drilling is a single-function cutting process. The machine tool is equipped with a rotating drill bit, which drills a cylindrical hole on the workpiece, and the feed direction of the drill bit is always in the axial direction. You can control the depth and diameter of the drill hole.
CNC Milling vs Drilling: Speed & Efficiency
The difference in speed and efficiency between the two is also significant. Let’s discuss CNC milling first. Since this process is cutting layer by layer, the processing speed is slow. But if you have a need for large-diameter holes, milling will be a very suitable machining method. On the other hand, if you have a large number of standard drilling needs, CNC drilling can be said to be the “king of speed,” which can complete a large number of drilling operations in a very short time. The reason is that it has an extremely high material removal rate (MRR).
For example, if you have a manufacturing requirement of 1,000 holes, CNC drilling may only take 20 minutes to complete all the work, while helical milling may take 2 hours.
CNC Milling vs Drilling: Precision & Tolerance
Many times, when we process parts, precision has always been a concern for customers. Although both of these are precision machining processes, in terms of accuracy, they are still different. CNC drilling is only suitable for general tolerances, and the accuracy range is generally between ±0.1 mm and ±0.05 mm. The actual situation also depends on the material and the size of the drill bit. In addition, CNC drilling process can control the size and shape of drilling, and the drilling depth can reach 2600 mm.
The accuracy of CNC milling is much higher, and it can reach the tight tolerance of ±0.01 mm. Therefore, this process is also often used to make various high-precision and complex components. For example, parts in the aerospace and automobile manufacturing industries are basically manufactured by CNC milling. This is because it is controlled by CNC interpolation, and the position is extremely precise. So, if your drawings require a tighter fit of H7 or higher, my suggestion is to choose the milling process.
Depth view: In the drilling process, the drill bit will exhibit a very subtle walking phenomenon when contacting the material. Although the diameter of the drilled hole is accurate after machining, the center of the circle may deviate from the theoretical coordinates by 0.05mm. Milling is processed by spiral interpolation, so the lateral force on the tool is relatively uniform. What’s more, it can also achieve position correction.
Considering the above, if your drawings have strict requirements on dimensional tolerances, drilling and reaming are the best options. But if strict positioning is required (such as Ø0.02 mm relative to datum A), milling is a better choice to prevent hole position drift.
CNC Milling vs. Drilling: Tool Movement
In fact, I don’t need to say more about this, the tool movement trajectories of the two processes are obviously different. CNC milling cutters are capable of moving in the X, Y, and Z axes and can run along complex tool paths. The drill bit for CNC drilling is simple. The drilling tool can only feed linearly in a single direction. After completing the corresponding processing, the drill bit can be returned along the original direction.
CNC Milling vs Drilling: Surface Finish
Since we are discussing the issue of machining accuracy, there is another part indicator that must be mentioned, which is the surface finish. It can achieve an extremely high surface finish on the surface of the part, and its surface roughness value (RA) can be as low as less than 0.8 μm. Additionally, this process can also easily process flat-bottomed holes, so once you need a sealed and beautiful part, milling is definitely your first choice.
Correspondingly, the roughness of CNC drilling is much worse. Since the entire cutting process involves the squeezing and tearing of the workpiece by the drill bit, the Ra value can generally only reach the range of 1.6-3.2 μm. If you want the surface to be drilled smooth enough, additional processing (such as reaming or boring) is required.
CNC Milling vs Drilling: Cost
I think that cost is also another issue that you are really concerned about. The CNC milling process is more complex and has a wide range of machining capabilities. Machining different materials and shapes of parts often requires the use of appropriate tools. The additional processes involved increase time and labor costs.
CNC drilling is different, it is cheaper. Because the process only involves simple tasks such as cylindrical holes. The machine is easy to set up, the cutting tools are cheap, and it’s ideal for mass production of drilled parts. These factors have greatly reduced the cost of the CNC drilling process.
CNC Milling vs Drilling: Applicable Materials
CNC milling is extremely adaptable, almost all materials can be processed, including metals such as aluminium, stainless steel, and copper, as well as plastics such as nylon, acrylic, and even wood and other materials. It can be said that CNC milling can be used to process parts from soft plastics and wood to hard steel, even titanium alloys.
The CNC drilling process is mainly suitable for relatively uniform materials. However, when you need to process some extremely hard or brittle material parts, you need to replace the appropriate drill bit for processing. Failure to do so may result in tool breakage.
Why are stainless steel and titanium alloys preferred for milling?
Engineers’ Insight: This is because during drilling, the drill bit is continuously cutting in the hole, and the chips are difficult to discharge, and the heat tends to gather in the drill tip, so like 304 stainless steel or titanium alloy, which has poor thermal conductivity and is prone to work harden, the high temperature of the drill bit can easily cause the surface of these materials to harden, which will burn the drill bit. However, milling is an intermittent cutting process. The cutting edge only contacts the material for part of each rotation, spending the rest of the time cooling in the air. This can play a good role in dissipating heat and preventing a hardened layer from appearing on difficult-to-machine materials. So, when you’re faced with difficult-to-machine materials, you should know what process to choose.
CNC Milling vs Drilling: Tool Type
The cutting tools used in the two processes are also very different.CNC milling uses milling cutters and supports multi-directional cutting. This tool is designed primarily for radial cutting, but also has some axial cutting capabilities. The advantage of milling cutters is size flexibility. You can use a 6mm milling cutter to process 6mm, 8mm or even 20mm holes through helical interpolation. In addition, milling cutters are also very rigid. They are usually shorter and harder than drill bits of the same diameter, and are less prone to deflection. As for common milling tool types, they include flat-bottom end mills, ball-end mills, etc.
CNC drilling mainly uses drill bits, which can be said to be specially used for axial cutting, that is, vertical downward penetration of the material. Drill bits generally adopt spiral drill structure, and each drill bit has standard specifications, so the drill bit can only process holes with exactly the same diameter. If you want to drill an 8.5mm hole, you must use an 8.5mm drill bit. Common drill bits include twist drills, center drills, etc.
Tooling Comparison Table
| Comparison Aspect | Drill Bit (Drilling) | End Mill (Milling) |
| Primary Motion | Axial / Plunging | Radial / Side Cutting |
| Tip Geometry | Conical Point (118° or 135°) | Flat Bottom or Ball Nose |
| Hole Flexibility | Fixed Size | Variable Sizes |
| Hole Bottom Shape | Conical (Pointed) | Flat (90°) |
| Best Application | Hole Making | Precision machining / Contouring |
| Cost Per Tool | Generally Lower | Generally Higher |
CNC Milling vs Drilling: Scalability
The milling machines used in CNC milling are highly scalable and can be applied to a variety of machining scenarios. Therefore, from small prototypes to high-volume production, the milling machine can complete the corresponding machining work. As for drilling machines, the scalability of this type of machine tool is insufficient. This machine tool can only process fixed-precision holes, so it is more suitable for mass production and repeated work.
CNC Milling vs Drilling: Noise and Vibration
CNC milling tends to produce significant noise. This is because milling is an interrupted cutting process. Adial force causes tool deflection during machining. And the high-frequency intermittent impacts can easily lead to chatter and produce a high-pitched whining noise. And how to suppress vibration during milling? In our factory, we usually use high-rigidity carbide tools and heat-shrink tool holders to process parts, which perfectly solves this problem.
Compared with CNC milling, CNC drilling is relatively quiet. The main reason is that the drill bit is under axial force during the drilling process. The vertical downward pressure helps to clamp the workpiece firmly in the fixture. The vibration of the workpiece is reduced.
Noise & Vibration Comparison Table
| Feature | Drilling | Milling |
| Cutting Mode | Continuous Cutting | Interrupted Cutting |
| Primary Force | Axial (Downward Pressure) | Radial (Side Pressure) |
| Vibration Risk | Low | Medium/High |
| Noise Profile | Consistent Low Drone | Variable Pitch (High whine if chattering) |
| Thin-Wall Safety | Low (Risk of Deformation) | High (Controlled Low Force) |
CNC Milling vs Drilling: Maintenance
Maintenance for CNC milling is relatively commonplace due to the broader range of moving components in CNC milling machines. You need regular laser interferometer calibration to maintain micron-level accuracy and clean up the chips generated during the milling process. At the same time, damaged milling cutters should be replaced in time. Because of its complex geometry, it is difficult to regrind.
Maintenance of CNC drilling is much easier. Drill presses have fewer mechanical structures, resulting in a lower failure rate. Moreover, dull drill bits can be reground for reuse. Lower maintenance costs translate to lower machine hourly rates. If your parts only need to be drilled, I recommend you to use CNC drilling technology.
Application of CNC Milling and CNC Drilling
1. CNC Milling Applications
- Mold making: It can be used to make various complex molds.
- Aerospace: Milling can manufacture complex aerospace components, such as landing gear components.
- Medical devices: The medical components are small in size, complex in shape, and the material is difficult to machine. Milling is the most suitable processing method.
- Rapid prototyping: Supports the production of prototyping and components for various industries.
2. CNC Drilling Applications
- Automobile manufacturing: The most widely used areas of drilling technology, such as the use of engine blocks, crankshafts, etc. in automobiles.
- Circuit board: Drill holes in the board to install electronic components.
- Construction: In the construction industry, it is necessary to drill holes in many steel beams and metal sheets.
CNC Milling vs Drilling: Core Advantages
Well, let’s summarize the core advantages of these two. You can visualize the advantages of the two through the table below.
Core Advantages Comparison Table
| Feature | CNC Drilling Advantages | CNC Milling Advantages |
| Primary Strength | Speed & Efficiency | Versatility & Precision |
| Cycle Time | Fastest for standard holes (Plunge only). | Slower, but combines multiple operations. |
| Hole Depth | Excellent for deep holes (High Aspect Ratio). | Limited depth (Tool deflection risk). |
| Tooling Economy | Low cost; easy to replace or regrind. | One tool can create multiple hole sizes. |
| Geometry | Ideal for cylindrical through-holes. | Can create flat bottoms, counterbores, & threads. |
| Surface Quality | Functional (Standard finish). | Superior (Mirror-like finish possible). |
| Best For | High-volume production & deep holes. | Prototypes, large diameter holes, & tight tolerances. |
If you read this table and still have doubts about which process to choose for your project, then I will give you a “rule of opinions”.
1. Deep Hole Factor
First, if your part has a hole depth greater than 5 times the diameter (aspect ratio > 5:1), selecting a drilling process is almost essential. Because if the milling cutter extends too far, its rigidity will drop sharply, resulting in severe vibration and dimensional deviation. This compromises the precision and accuracy of your parts.
2. Tool Changing Factors
Changing tools is also a common process in your machining process, but it is also a key factor. If you need three holes of 9mm, 9.2mm and 9.5mm on a part, then when you use CNC drilling, you need to purchase 3 types of drill tools, and the machine will need to replace the tool 3 times. And when you use CNC milling, you only need a standard 6mm end mill. The machine only needs to adjust the path radius of the helical interpolation to perfectly process these three dimensions.
In addition, I would like to tell you that when CNC milling holes (helical interpolation), a general rule of thumb is: the milling cutter diameter is approximately 60% ~ 75% of the hole diameter. This ratio not only ensures that the tool is strong enough but also leaves enough space for the chips to be discharged smoothly.
In Conclusion
That’s all about the comparison between milling and drilling. I believe that by reading this article, you should now have a clear understanding of which process to choose. In fact, in the final analysis, there is no better process, it simply needs to suit your budget and delivery time. In addition, our DSR factory has both milling and drilling processes available. If you’re still struggling with process selection, please upload your CAD file and let our experienced engineers provide you with a free process analysis and quote.
FAQ:
Q1: What is the golden rule of milling?
A: In fact, the golden rule of milling can be summarized in two sentences. First, maintain a suitable chip thickness per tooth. Second, try to use a higher speed and sufficient feed to avoid frictional heat generation caused by low feed rates.
Q2: What are the disadvantages of CNC milling?
A: The main disadvantages are as follows:
- Higher cost investment in equipment, tools, fixtures and software
- High dependence on programming, clamping, and parameter setting
- During subtractive processing, more chips will be generated, and the tool is also easy to wear
- Milling is difficult to handle thin-walled structures
- Requirements are placed on the proficiency of the operator
- Thicker workpieces require longer machining times
Q3: What are the disadvantages of CNC drilling?
A: The main disadvantages of CNC drilling are as follows:
- The function of CNC drilling is relatively simple, mainly drilling processing
- The process relies heavily on cooling, clamping and positioning accuracy, and any deviation may lead to hole position errors.
- Deep hole machining requires special drill tools
- Drilling is not effective for very hard materials
- Constant drilling work can lead to overheating, which may damage the workpiece or wear the tool.
Q4: Which companies specialize in CNC milling and drilling contract manufacturing?
A: The companies that can provide you with excellent CNC milling services and CNC drilling services are: Xometry, Protolabs, Astro Machine Works, DSR, Cox Manufacturing, etc. For more specific content, you can refer to another article on our site—Top 10 Precision Parts Machining Manufacturers.
Q5: Can a Drilling Machine be Used for Milling?
A: Generally speaking, it is not recommended because the support methods and force designs of the two processes are different, which can easily cause many processing problems, including vibration, tool deflection, etc. You may also use a drill machine to do a small amount of light-load milling, such as simple grooving and workpiece surface repair.
Q6: What type of drill is used for deep holes?
A: For deep hole machining needs, we usually use gun drills or BTA/STS deep hole drills.
