CNC Milling vs CNC Drilling: Which One to Choose?

The capability of CNC machining to create complex and precise parts comes with its diverse machining processes, such as milling, turning, drilling, and others. Here, we will focus on milling vs drilling to understand their unique capabilities to help you choose the appropriate machining approach.

Although you can use any process (or combination) to convert your design into a functional product, which one to use depends on design specifications and final requirements. So, let’s compare working, tool setup, offered precision, advantages, applications, and other aspects of milling and drilling.

What’s CNC Milling? 

CNC Milling is a versatile machining approach that precisely cuts workpieces to intended shapes using different rotating cutting tools. Here, inputted digital instructions (G & M Codes) in the CNC milling machine dictate the tool movements and remove material. This control- automation produces consistent and repeatable parts from digital designs. 

what is cnc milling

The milling is suitable for intricate designs with fine details due to the multi-axis movement of tools. Similarly, it can perform many operations like cutting, drilling, and engraving. As a result, milling is applicable in industries requiring intricate parts with tight tolerances. 

What’s CNC Drilling?

CNC drilling is another subtractive manufacturing approach that focuses on creating precise holes in the workpiece according to the uploaded CAD design. It generally involves a single-axis movement. The drilling machines utilize computer-controlled rotating drill bits to create the holes. Meanwhile, the drill bit size is exactly or slightly less than the desired hole diameter. 

high speed drill

Unlike other operations, CNC drilling processes specialize in hole drilling for different applications. With respective drills, you can make straight, centric, counterbore, countersink, tapped, reamed, and other types of holes. 

The drilling techniques are crucial in applications such as electronic components, automotive & aerospace parts, and mechanical assemblies. 

Differences Between CNC Milling and Drilling: Quick Comparison

CriteriaCNC MillingCNC DrillingWorking ProcessThe milling tool rotates and feeds the material to obtain the desired shape.Rotating drill-bit advances inside the material and creates cylindrical holes.Motion PathHorizontal and vertical motion.Vertical motion pathTooling and SetupEnd mill, face mill, drill bit, or fly cutter. Precision and CapabilitiesHighly preciseLess precise than millingMaterial TypesMetal, alloys, plastics, and compositesUnable to process hard metal and alloysSurface Finish QualityMore fine as-machined finishSlightly high roughnessSpecific Industries and ApplicationsFrom simple pistons to advanced aerospace parts.Limited to hole drilling applicationsCost ConsiderationsCostlierLess costlyLead TimeComparatively slow turnaroundRapid turnaround

Compare Differences Between CNC Milling and Drilling in Detail

These two CNC processes are renowned for their exceptional machining capabilities in different domains. They both have similar machine setups, precision, and control mechanisms. But what is the difference between milling and drilling? Let’s point out the differences in detail, examining different comparison criteria. 

Working process

The CNC milling machines convert the uploaded CAD designs into computer instructions that decide the tool control. Next, the workpiece is attached to the vises, clamps, or fixture plates. As the tool(generally end mill) moves to the initial milling position, the rotating tool starts to feed the material with a pre-determined feed rate and speed. At the same time, the muti-axis movement allows the tool to move across the workpiece and shape it. 

Furthermore, there can be two distinct workpiece movements in CNC milling. First, the workpiece moves in the same direction the tool rotates, called climb or up-milling. In the second case, the tool rotates against the direction of feed, called conventional or down milling.

The drilling works by removing the material from the area where the hole is needed using a rotating drill tool. As in CNC milling, the computer controls the drilling tool. After positioning the workpiece to the drilling coordinate, the bit starts to rotate and advances into the material (typically along the Z-axis) to create a precise and clean hole.

Motion Path 

One significant difference in milling vs drilling is the motion path of cutting operations. During the operation, the milling cutting tool moves horizontal and vertical motion parts, allowing for more versatile and complex shapes. 

In contrast, attachments primarily move in a vertical motion path during drilling operations. This is because drilling focuses on creating holes or material removal from a specific point. 

Tooling and Setup

Usually, CNC milling involves an end mill, face mill, drill bit, or fly cutter to process the material. The correct machine tool is necessary for efficient and accurate milling. Saying that drill bit and end mill is the most common. Therefore, you need to consider material type, cutting edge, tool coating, shape & size, and other factors while choosing the end mill vs drill bit. Afterward, work materials get fixed on the machine table, where tool paths align perfectly.

end mills

The drill bits for CNC drilling operations are chosen about the work material, hole depth, size, hardness, and finish quality. Also, some complex drilling might require custom or specialized tools. The tool attaches to the spindle, and the workpiece gets fixed to the machine table.  

Precision and Capabilities

These are among the most precise manufacturing processes. They offer eye-to-detail machining processes with high precision. For illustration, the milling produces parts precise as ±0. 005’’(0.127 mm), whereas drilling can achieve tolerance as low as ±0.002″(0. 05 mm)

Milling can create intricate parts or products, from simple slots to complex automotive engine components. On the other side, drilling is focused on creating holes of different shapes and sizes. It can drill a hole up to a depth of 2600 mm and 3 – 32 mm diameter. 

Material Types

Both processes are compatible with metal, plastics, and composites. So, they can work on a wide range of materials to fulfill numerous manufacturing needs. 

Common Drilling Materials 

  • Steel
  • Aluminium
  • Brass
  • Stainless Steel 
  • Hardened plastics, like Polycarbonate and PEEK 

However, milling has more material capabilities than drilling. Drilling is incompatible with hardened tool steel, certain ceramics, and some titanium alloys that milling can work with.  

Common Milling Materials

  • Steel
  • Aluminium 
  • Brass
  • Inconel
  • Garnet
  • Titanium
  • Tungsten 

Surface Finish Quality 

CNC milling employs multi-axis movement and diverse tooling, resulting in a versatile as-machined surface finish. The roughness value (Ra) of the milled surface can reach as low as 1.6 µm. Consequently, the drill surface can achieve a Ra value of 3.48 µm. However, the Ra value is affected by depth of cut, material, RPM, and other factors. 

Hence, surface finish by milling is finer than drilling because of cutting dynamics. Still, drilling offers a better surface with the holes. Additionally, milling deals with exterior machining, making it easy to achieve superior machined surfaces. 

Specific Industries and Applications

custom cnc milled parts

Application is probably the most critical comparison aspect in milling vs drilling because it determines where these processes are applied. CNC milling can machine any flat surface precisely to any complex angle, such as curved and undercuts.  

Applications of CNC Milling 

  • Automotive parts like cylinder heads, engine blocks, gearbox housing, and more
  • Prototyping for various industries.
  • Medical equipment’s components and implant
  • Mold and tool manufacturing 

CNC milling is preferred in more diverse areas than drilling as it can craft detailed geometries. Still, drilling is indispensable where precise cylindrical features are needed.

Applications of CNC Drilling 

  • Deep and small holes in diverse materials.
  • Drilling holes for fasteners in airframes and engines of aircraft.
  • Automotive assemblies.
  • Precise & consistent holes in electronic boards to place the components.

Cost Considerations

CNC drilling and milling both are cost-effective manufacturing methods. They justify the cost with precision, complexity, and rapid turnaround capabilities. However, CNC milling processes are slightly costlier in a head-to-head comparison of drilling vs milling. 

If we break down the cost factors and considerations, milling costs vary on complexity, workpiece material, machine setup, production speed, and operation numbers. Meanwhile, drilling costs are affected by drilling depth, hole diameter, and number of holes. 

Lead Time

Generally, CNC milling operations have a longer lead time due to intricate and complex parts machining. In contrast, CNC drilling projects offer shorter lead times because drilling is more straightforward machining focused on hole-making tasks. 

However, several factors decide the lead time of any specific milling or drilling project. For example, milling lead time depends on machining intricacies, material type, setup time, required precision, and operator skill. Similarly, drilling lead time is influenced by hole number, depth, diameter, and equipment & tool setup times. 

Advantages of CNC Milling and Drilling

These processes bring various advantages of precision, cost, complexity, and production speed for diverse materials and applications. However, these operations also have individual benefits where they find their applications. 

cnc drilling on brass

Advantages of CNC Milling

  • It creates complex and versatile shapes with exceptional accuracy, from simple piston machining to advanced aerospace parts.
  • The automation of milling eliminates human error, contributing to precise results.
  • CNC milling machines can work with different metals, alloys, plastics, composites, and ceramics. This material versatility opens its application possibility in every industry.
  • Produce identical parts with consistent precision and quality, cost-effective for prototyping to mass production.
  • The as-machined surface finish of milling is smooth. Although, it might leave some tool marks that require post-processing.

Advantages of CNC Drilling

  • It brings high precision to hole-making tasks, superior to any traditional drilling method for consistent and accurate hole dimensions.
  • This method is highly cost-effective for large-scale production.
  • Drilling is a quick process and can perform repetitive tasks consistently. 
  • It can create holes with various shapes and sizes, from a few mm in diameter to 4 cm and up to a depth of 2600mm.
  • Like milling, drilling is compatible with large material types.

Disadvantages of CNC Milling and Drilling

Like every other manufacturing method, milling & drilling have some disadvantages. So, let’s unfold some capabilities and cost drawbacks of these processes.

Disadvantages of CNC Milling

  • The expensive price of CNC milling equipment and tool setup demands high upfront costs.
  • Tool changing for multiple operations increases machine downtime.
  • The workpiece size that can be machined is constrained due to machine capabilities. 
  • The milling machining generates noise, deburr, and material waste. 

Disadvantages of CNC Drilling 

  • Drilling is limited to hole creation, making it less versatile than milling.
  • It is challenging to drill hard materials like steel, titanium, and hardened steel.
  • The continuous drill causes excessive heat generation and can damage the workpiece and wear the tool. 
  • It requires separate drilling tools for different materials. 

CNC Milling vs. Drilling: How to Choose the Right Technique for Your Project

Choosing between milling vs. drilling entirely depends on the design and project specifications. After all, it is all about obtaining the functional and dimensional requirements in the final product. If your project is of complex shape, requires a smooth finish, tight tolerances, or has several features, CNC milling is the right choice for you. On the other hand, CNC drilling is the go-to option for any precise hole-drilling project. 

At RapidDirect, We provide comprehensive CNC machining services, including CNC milling, turning, routing, and drilling. We have extensive experience in handling CNC projects for diverse industries. Our services extend from rapid prototyping to custom machining for your unique needs.  

Choosing us for your machining projects ensures speed, precision, and quality with a customer-centric approach. Our expert engineers and operators balance cost and quality with every machined part. So, upload your design file and get an instant quote to start your project!

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