CNC milling is a versatile machining process known for precision and complex parts. It involves different techniques/operations and can accommodate diverse tooling; end milling is one of them. In fact, this is the second most popular machining technique after CNC turning.
Different tooling options, high material removal rate, precise finish, and some other factors make this process widely used across industries.
This article will elaborate on what is end milling, compatible cutters, applications, benefits, potential challenges, and machining considerations.
What is End Milling?
Like every other subtractive manufacturing process, end milling involves the use of rotating cutters with multiple edges to remove material until desired shapes and features are formed. It crafts complex and intricate features on metals, alloys, plastics, composites, and other engineering materials.
What makes end mills different from other tools is the helical design of cutting edges. The cylindrical-shaped shank contains tooths on both ends and sides, so they cut the workpieces from multiple directions.
Moreover, a variety of CNC end mills(square, ball nose, corner radius, etc.) allow you to work with multi-feature 3D shapes. With the right cutters, you can make complex contours, deep holes, pockets, slots, flat profiles, recesses, etc.
Anatomy and Terminologies
Before moving into further discussion, let’s look at its anatomy and key terminologies;
- Shank: The cylindrical part of the mill that is clamped into the machine’s spindle or tool holder.
- Neck: The reduced diameter section between the shank and the cutting portion for deeper reach and clearance.
- Flute: The helical grooves along the end mill’s body, which form cutting-edge during machining.
- Cutting Diameter: Diameter at the widest point of the edges.
- Cutter Sweep: The arc or path formed by the cutting edge during rotation.
- Cutting Length: The axial length over which the cutting tooth’s edges engage in material removal during milling.
- Helix Angle: The angle between the end mill’s helical flute and its centerline.
How End Mills Work?
A specialized end mill machine or regular CNC machine accommodates suitable end mill tools in its spindle (or other rotating components). Then, it controls the movement precisely across the workpiece in a pre-determined tool path.
The size of the cut, depth, speed, cycle time, and all other variables depend on CNC inputs and geometry & end mill sizes.
The detailed steps for How the end mill works?
Part Design and Programming
A detailed design of the part to be end-milled is created first, outlining all features, dimensions, and machining directions. While creating the design, it is essential to consider the capabilities of end mill cutters; what kind of shapes they can machine?
Machine Setup
The end milling cutter is secured in the spindle’s collet or tool holder, whereas the vice, clamps, or fixture hold the workpiece. Consequently, the position of the workpieces is parallel to the table or the spindle axis. The value of the input parameter depends on the work material and tool coating. The operator sets the reference point (work offset) after setting tool and work.
Milling Process
Once the program is run, the spindle rotates the end mill tool, and then the cutting edges interact with the material and form the chips via shearing. Edges at the end perform axial cutting and side edges perform radial cutting, whereas helical flute design facilitates easy chip removal.
The entering angle and cutting path depend on the CNC program. The same program codes dictate the spindle to move the cuter across the axes( X, Y, Z).
Types of End Mills and Their Applications
Based on the geometry of machining edges and application preferences, there are different types of mill bits for the end milling process. The tip (end) shape and flute characteristics make them distinct from each other.
Let’s discuss some common CNC end mills shortly;
Roughing End Mills
These end mills remove a large amount of material while leaving a relatively rougher surface finish. The rugged or wavy edges and larger core diameter allow for heavy cuts with minimal vibration.
Application: Heavy-duty machining of steel, aluminum, iron, and other metals. E.g. Molds, shipbuilding, pre-finishing auto parts, etc.
Ball End Mills
A ball end mill is characterized by the hemispherical tip (nose) with a two or four-flute design. These mills can cut the works in a continuous path crafting complex 3D contours, curves, and concave profiles. You can use the ball nose end cutters for facing, pocketing, profiling, filleting, etc.
Applications: 3D contour machining for molds and die, sculpting automotive and aerospace parts, adding fillets on complex designs, etc.
Corner Rounding End Mills
A corner rounding type of end mill involves a radius at the tooth edges, which removes the material from work to achieve a rounded corner or specific radius. You can choose the radius size of these milling bits according to your requirements.
Applications: Deburring, filleting (or radii on sharp edges), aesthetic finishing, and transition curves between contours in complex parts.
Square End Mills
As the name suggested, these cutters involve a flat and square tip perpendicular to the tool’s rotational axis. This geometry crafts perfect 90-degree edges, corners, and flat bottoms on the workpiece. Thus, square mills are popular for general purposes in machining tasks.
Applications: Keyways, slots, external contours, vertical cutting, flat bottom holes, and flat surface smoothing.
Dovetail End Mills
Dovetile or fishtail milling cutters are defined by angled edges for cutting (matching the desired dovetail profile) that are available in standard angles like 45°, 60°, and 90°. You can choose them to create dovetail-shaped grooves or profiles.
Applications: Slots & sliding fixtures, dovetail joints, grooves, notches, undercut features, etc.
Finishing End Mills
It is a sharpened and fined end mill, designed to achieve tighter dimensional tolerances and smooth surface qualities. The bit design includes a higher number of flutes (2 to 6) and larger helix angles to achieve lower roughness levels, down to Ra 0.4 µm.
Applications: Different industrial items requiring smooth finish for performance, such as medical device parts, heat sinks, measurement instruments, vehicle engine parts, etc.
V-bit End Mills
These are the milling cutters with a V-shaped tip formed by tooth edges in 30, 60, or 90 degrees. The sharp conical tips in V-milling bits make them suitable for chamfering, engraving, and 3D carving.
Applications: V bits engrave Signs, logos, symbols, numbers, and letters on the work surface. Consequently, they are also applicable for chamfering and narrow-cuts.
Materials Used in End Milling
You can choose different plastics, metals, alloys, and composites to machine with end milling processes. Material selection is directly related to tooling and machining conditions; suitable tool coating and milling variables are different from one to another material type.
The table below outlines the common materials, and what is the right End Mill for them;
Material | Characteristics | End Mill Features | Grades/Types |
Aluminum Alloys | Lightweight, easy to machine | High helix angles, polished flutes | 6061, 7075, 2024 |
Steel & Stainless Steels | Strong, wear-resistant | High Speed Steel (HSS ) or carbide, TiCN coating | AISI 304, AISI 316, AISI 1018, AISI 1045 |
Titanium Alloys | Strong, corrosion-resistant, hard to machine | Variable helix designs diamond-like carbon (DLC) coating | Grade 5 (Ti-6Al-4V), Grade 2 |
Plastics | Lightweight, prone to melting | Sharp edges, single or double flutes | Acrylic, Polycarbonate, Nylon, Delrin, PE, PP |
Composites | Abrasive, risk of delamination | Compression end mills | CFRP, GFRP, Kevlar, Epoxy, Thermoplastics |
Applications of End Milling in Various Industries
Various precision machining features are possible to create with a CNC end mill, flat surfaces, complex profiles, channels, holes, etc. So, its uses are diverse; from general consumer items to industries requiring tight accuracy.
The following are some major application sectors ;
Aerospace Industry
End milling operations are useful in the production of complex components such as engine mounting and bracket housings in aerospace. These components are typically made with aluminum and have very high requirements for accuracy and quality. Other examples are
Aircraft wings, turbine cartridges, and surface roughing of many other components.
Automotive Components
CNC end mill cutters create both rough and smooth finish automotive components; the level of precision, fine details, and surface quality makes them more favorable in vehicle manufacturing. You can make engine parts, valve seats, transmission housings, oil channels wheel hubs, etc.
Moreover, this milling approach also addresses the growing demands of EVs, like motor elements, batter housing features, and drivetrain components.
Precision Parts for Electronics
Miniaturization and accuracy are key demands for electronics parts; carbide end tools are used to make Printed Circuit Boards (PCBs). For instance, smooth holes, and keyways facilitate smooth connection. Other uses include enclosures for electronic devices, mounting components, thermal management elements, etc.
For Medical Devices
Accurate dimensions and finish are critical in medical device manufacturing, directly impacting treatment effectiveness and safety. End milling can process medical-grade titanium, stainless steel alloy, and some plastics to create diagnostic devices, implants, and surgical tools. Additionally, it also allows for the customization of implants according to patient needs.
Prototyping and Custom Part Manufacturing
Engineers and manufacturers use multi-axis CNC end milling machines to test and refine designs. They can produce intricate designs in metals, plastics, and composites. For example, molding tools, jigs, fixtures, custom parts, etc.
Benefits of End Milling
- An end mill cutter performs multiple operations like cutting, plunging, fattening, profiling, contouring, etc.
- It provides high machining precision and accuracy, down to ±0.05 mm in standard and ±0.002 mm in precision milling.
- It involves cutting in or across all four axes of a spindle, which enables to creation variety of complex shapes and surfaces.
- The operation’s accuracy minimizes the number of additional finishing processes. A typical range of the as-machined roughness level is 6.3 to 0.8 µm.
- The multi-flute design and coating allow for deeper cuts.
Common Challenges in End Milling and How to Overcome Them?
Like every other CNC process, it has its own difficulties and limitations. Understanding these challenges and strategies to mitigate them helps to avoid machining issues and achieve the desired result.
Chattering, excessive tool wear, poor finish, and heat buildup are common challenges. Let’s discuss these challenges more briefly and how you can overcome them;
Dealing with Chatter and Vibration
Machining chatter and vibration are mainly associated with machine stability and tool rigidity. Long overhanging tools, loose clamping of work, and wrong cutting angles cause this periodically self-excited vibration.
Prevention: Using vibration dampers or absorbers is the in-process method to mitigate the chatter. During setup, ensure stability, optimize cutting variables, and clamp the workpiece securely.
Potential for Tool Breakage
Although it is a rare phenomenon, tool breakage can occur if there is excessive cutting force, chatter, hard workpiece, incompatible tool geometry, chip packing, or thermal stress. Over time a CNC end mill cutter becomes dull and its angle’s wings get ripped off. Moreover, tool breakage not only results in part failure but also poses a critical safety concern.
Prevention:
- Optimize the tool path
- Use the correct feed and speed
- Monitor the process continuously,
- Choose an end milling cutter with a suitable coating (E.g. TiAlN, DLC)for hard work materials.
Requires Specialized Setup
You might need custom fixtures and calibration tools for perfect alignments during the setup. This is more complex than standard milling and requires a high level of expertise. Additionally, it can be time-consuming for small batches and prototypes.
Prevention:
- Use modular and adjustable fixtures to reduce setup complexity
- Perform CAM simulation to analyze setup and tool path before actual machining.
Heat Generation
During the operation, cutting edges move against the works or they contact each other periodically, leading to friction. When any imbalance happens in processing, friction increases, which deforms the edges and converts mechanical energy into heat.
Prevention:
- Use suitable coolant type and flow
- Do not push extra feed and speeds, balance these with productivity
- Keep the rake angle positive
- Monitor the tool rubbing and take the correct action right away
- Often, climb milling effectively transfers the heat into the chip.
More Expansive
Manufacturing parts with end milling are more expensive than conventional or standard milling operations. The reasons are simple; expensive tooling, demand for experienced operators, complex machine setup, etc. To keep the cost of end milling in balance, you can use high quality tools, leverage automation, and choose efficient tool paths.
Key Considerations of Using End Mills
Select the Right Tool Material
High Speed Steel (HSS) and Carbide are the two main end-mill materials. HSS tools are affordable and work best with plastics and soft metals like aluminum. On the other hand, carbide is harder than HSS and suitable for high-speed machining and hard materials like titanium and tool steel. For more robustness, you can choose these tools with hard coating, such as TiN, TiAlN, or DLC.
Use the Correct Flute Count
Although tools with different flute numbers are in practice, typically 2 and 4-flute end cutters are popular in machining shops. The main difference between the 2 vs 4 flute end mills is the cutting speed and finish quality. As the number of flutes increases, it can cut harder materials and the finish level also improves. On the other hand, low flute numbers provide faster cutting speed. So, choose the right count accordingly.
Control Depth of Cut
Highly deep cuts cause heat generation and shallow cuts reduce the speed, therefore controlling the cut depth is essential. There are two general rules for maximum depth; either half of the mill diameter or less than the length of the flute. For smooth finishes, you might need to control the depth up to 10-20 % of the tool diameter.
Optimize Feed Rate and Speed
Set the right feed and speed by considering factors, material properties, tool rigidity, tool geometry, and capabilities of CNC machines. The best suggestion is to follow the manufacturer’s guidelines(charts) and incremental adjustments for fine-tuning. Moreover, you can also use online milling speeds and feeds calculator to find out the optimal speed and feed.
Use Coolant or Lubrication
As previously said, heat is one of the common challenges and you must use suitable coolant or lubrication to avoid this. Lubrication reduces friction and coolant stabilizes the temperature of the machining area. There are different options for coolants, oil-based, water-based, synthetic, etc. Moreover, you can apply these either by flood coolant or MQL method.
Maintain Proper Tool Holder Balance
A correct tool holder balance is essential to reduce the vibration and achieve optimal milling performance with minimal tool wear. There are two ways of balancing; static and dynamic.
Static means measuring imbalance while the tool holder is stationary, whereas dynamic (or high-speed) approach involves rotating the tool holder at operational speeds to detect and correct imbalances.
Regularly Inspect the Tool
You can integrate real-time monitoring systems to inspect the tool’s wear, scratches, tear, and dullness. Schedule a periodic inspection and use checklist to ensure the too condition. Furthermore, continuously track the inspection results and performance over time to decide when to change your tool.
Difference Between End Milling and Face Milling
Face milling is a more specialized operation and focuses on flat workpieces, removing large amounts of material to achieve surface flatness. Often, face mills are used in preparatory steps before performing complex machining tasks. Unlike an end mill cutter, a face cutter tool involves a large and flat face with edges around its periphery.
The face mill vs end mill table below outlines their key differences;
Aspect | End Milling | Face Milling |
Cutting Tool | Small cutters, edges on the sides and end. | Large and flat cutters, edges on the face. |
Tool Movement | Vertical or angled movement | Horizontal or flat movement |
Chip Formation | Complex and discontinuous chips | Large and continuous chips |
Speed | Lower cutting speeds | Higher cutting speeds |
Surface Finish | Good for precision but rougher than face milling | Smoother finish on large workpieces, Ra ( 0.8 – 1.6 µm) |
Applications | Detail work, pocketing, profiling | Surface finishing, flattening, large cuts |
Best for | Small parts, deep slots, narrow spaces | Flatening and surface smoothing |
Tool Life | Longer under proper use and maintenance | Faster wear due to higher cutting forces |
How RapidDirect Supports Your Milling Operation Needs?
Considering the end requirements and arranging the right end mill type is essential for any end milling project, which we completely understand at RapidDirect. Our engineers closely work with you until your parts are delivered, including design optimization assistance, material selection, and finishing recommendations.
Furthermore, our in-house factory has milling machines with the latest CNC integration that tackles custom and complex designs with high precision.
- Instant quotation & design feedback
- 20+ end milling operations
- Custom tooling for complex parts
- Milling Prototypes and full-scale production
- 100+ material options
- Streamlined manufacturing and quick leads
Whether you are a small startup or an established brand, our CNC milling services can provide high-quality parts across industries, strictly in compliance with your design.
Conclusion
Overall, the end milling process enables to creation of intricate features and profiles on various types of workpieces. The use of the right type of cutter, milling variable, and setup is essential to make parts with high geometrical complexity. Furthermore, understanding its possible challenges before the machine runs helps to prevent defects and risk of failure.
This process is helping innovations of complex mechanical structures for industries and continuously pushing the manufacturing precision and efficiency.
FAQ
Based on geometry and specific uses, there are many types; flat, ball nose, roughing, finishing, corner radius, and tapered end mill.
Choosing the right CNC end cutter requires considerations of the material, cutting type (roughing or finishing), geometry (flutes, shape), machine capability, and surface finish.
Drilling cuts axially for cylindrical hole creation, whereas end bits work in both axial and radial directions for slots, grooves, channels, and intricate contours.
The name comes from its functionality—it involves cutting edges at the end and sides, which allows for multi-directional material removal.
A milling cutter is a broad term including end, face, and slab mills. On the other hand, a ball-end mill is a specific type that involves a hemispherical tip for machining 3D contouring and complex surfaces.
You can determine the material feeding rate using the given formula; Feed= Spindle Speed (N) x Chip Load per Tooth (Z) x Flute Count.