Undercut machining allows you access to parts such as molds and dies that standard machining methods cannot.

This article aims to focus on the basics, types and applications of undercut machining, so you’ll have a better understanding.

What is Undercut in Machining and Manufacturing?

Undercut machining refers to the process where material is removed from beneath the top layer or surface of a workpiece. This is often done to create a recess or groove that allows for the assembly of parts or to enhance the geometrical intricacies of a component.

Undercuts are typically challenging when machining parts because they may require specialized tools, such as lollipop cutters or T-slot cutters, to reach and remove the material effectively.

Undercuts allow for the assembly of components that would otherwise be difficult or impossible to achieve with conventional machining processes.

What is the Purpose of Undercut Machining?

The primary purpose of undercut machining is to enable the production of complex parts with internal or hidden features that are integral to the functionality or assembly of the product.

These features often allow for the integration of additional components, improve the aesthetic appeal, or meet specific engineering requirements that cannot be achieved through standard machining practices.

How Does Undercut Machining Work?

Undercut machining involves six main stages, each critical to achieving the desired outcome in manufacturing parts with complex geometries:

1. Design and Planning: The first step involves detailed planning and design, where engineers use CAD software to create a digital model of the part, including all necessary undercuts. This stage requires careful consideration of the material, the geometry of the undercuts, and the end-use of the part to ensure feasibility and functionality.
2. Selection of the Appropriate Tool: Choosing the right tool is crucial for effective undercut machining. Tools such as lollipop cutters, T-slot cutters, and dovetail cutters are selected based on the type and location of the undercut. The tool must be capable of reaching the undercut area without interfering with the rest of the part.
3. Setup and Fixturing: Proper setup in the CNC machine is essential to ensure accuracy. The part must be securely fixed, and the tool must have the correct orientation to access the undercut region without causing damage to the part or the tool.
4. Machining Process: The actual machining process involves the CNC machine moving the tool along the predetermined path to remove material and create the undercut. This step must be precisely controlled to maintain the integrity of the part and achieve the required specifications.
5. Inspection and Quality Control: After machining, the part undergoes a thorough inspection to ensure that all specifications are met. This may involve using measuring instruments or 3D scanning to verify the dimensions and integrity of the undercuts.
6. Post-Processing: Depending on the material and the end-use of the part, post-processing such as deburring, polishing, or heat treatment may be necessary to prepare the part for use.

What are the Different Types of Undercuts?

The two main types of undercuts are internal and external undercuts. Let’s get into details for both of them

Internal Undercut

An internal undercut is a feature hidden inside the part, not visible from the external surfaces. This internal geometry is crucial for creating non-visible locking mechanisms or aligning features within a component, often used in complex assemblies like gear hubs or consumer electronics.

External Undercut

Conversely, an external undercut involves cutting away material from the outer surfaces of a part. These features are typically used to ensure a proper fit between components, such as in dovetail joints or interfaces where parts must interlock securely.

Here is how undercuts work in different machining operations:

• Turning: In turning processes, undercuts are known as necks or relief grooves. These are essential for providing clearance at the end of threaded parts or along shafts, where tools need to transition smoothly without colliding with other parts of the workpiece.
• Molding: During molding, undercuts serve as indentations or protrusions that can complicate the mold release process. They are strategically placed to ensure the integrity of the molded part but require careful planning to allow for easy removal from the mold without damage.
• Milling: Milling undercuts involve the removal of material from areas not directly visible from the spindle’s position. This process often requires specialized tools like lollipop cutters or extended reach end mills to create features like internal pockets or specialized slots.
• Etching: In microfabrication, undercuts from etching are typically unintended consequences of the etching process, which can affect the precision of the micro-structures being created. These undercuts are considered during the design phase to minimize their impact on the final product.

Now, that you know that undercuts are either internal or external let’s get into details on the specific operations used to achieve them.

What are the Different Types of Undercut Machining?

These various undercut techniques are essential for components requiring complex geometries and are widely used across various industries, including aerospace, automotive, and medical technology.

Lollipop Cutting

Lollipop cutting utilizes a spherical-shaped cutter, commonly referred to as a lollipop cutter, due to its resemblance to the candy. This type of cutter is specifically designed for machining undercuts and difficult-to-reach areas within a component.

The cutting angle of lollipop cutters can vary depending on the application but generally ranges from 30° to 60° to maximize accessibility and cutting efficiency. Lollipop cutters can vary significantly in terms of materials, but they are often made from high-speed steel (HSS) or carbide to withstand the stresses of undercut machining.

Lollipop cutters are typically used in the aerospace industry for creating complex internal shapes within components, where traditional end mills cannot reach. They are crucial for the manufacture of turbine blades, structural aircraft components, and intricate assemblies requiring a high degree of precision.

Slot Cutting

Slot cutting involves creating a narrow groove or slot in a workpiece, typically used for keyways or channels within mechanical assemblies. This technique employs specific types of end mills and slot cutters that can produce precise and clean cuts, allowing for components to fit together seamlessly.

Common applications of slot cutting include creating slots for electrical wiring in aerospace components, slots for mechanical linkage in automotive transmissions, and channels in high-performance sports equipment for structural reinforcements.

The standard tool angle of slot cutting typically ranges from 5° to 30° to ensure efficient material removal and minimize tool stress.

T-Slot Cutting

T-slot cutting is a specific type of slot cutting used to create a T-shaped slot in a workpiece. It is primarily used for mounting and clamping applications in machine tool setups, providing a secure anchor point for fixtures.

T-slot cutters are available in standard widths ranging from 3mm to 40mm, with depths adjusted to create the characteristic ‘T’ profile needed for specific applications. T-slot cutting is integral to the manufacturing of machine tables, workholding devices, and modular assembly systems where components need to be easily adjustable and securely fastened.

Dovetail Cutting

Dovetail cutting is used to machine angular grooves into a workpiece, resembling the ‘dovetail’ shape commonly seen in woodworking. This type of cut provides a very strong mechanical interlock, preventing parts from slipping in one direction.

The angles typically used are 45 and 60 degrees, though custom angles up to 120 degrees can be specified for specific applications. Dovetail cutting is frequently used in the assembly of parts that require a high level of mechanical strength and stability, such as in aerospace component fittings and metalworking jigs.

Spherical Undercutting

Spherical undercutting involves machining a spherical or partially spherical cavity into a part, which is not accessible with standard end mills due to the undercut nature of the shape.

This technique is essential for creating cavities in molds, aerospace components, and automotive parts where spherical shapes are required for assembly or aerodynamic purposes. The cutting width and depth for spherical undercutting are closely controlled to ensure the integrity of the workpiece and the functionality of the machined feature.

One-Sided Undercutting

One-sided undercutting involves machining a feature on only one side of a part, which is particularly challenging because it restricts the access and visibility of the cutting tool. This method is typically used to create slots or grooves that are not radially symmetrical.

This technique is frequently used in the automotive industry for creating non-symmetrical grooves in engine components where assembly constraints exist. It’s also employed in consumer electronics to integrate components within compact spaces.

Generally, these tools have a narrow angle to allow for precise cutting without interfering with other parts of the workpiece. The width and depth are critical and must be precisely controlled to ensure the feature fulfills its purpose without weakening the structure of the part.

Back Boring

Back boring is used to machine features on the back side of a hole or an existing feature, which is inaccessible from the front. This technique is crucial for operations requiring the enlargement of holes from the opposite side of the initial entry or for internal cavities that must be accessed through existing holes.

Back boring is essential in aerospace for modifying engine components or airframe parts where access is limited to one side only. It’s also used in high-precision assemblies where features must align perfectly across different parts.

Thread Milling

Thread milling is a versatile and precise undercut machining technique used for cutting thread profiles within a workpiece. It offers advantages over traditional tapping due to its ability to produce threads of various sizes with the same tool, its suitability for difficult materials, and its capability to create both internal and external threads.

This technique is extensively used in the aerospace and automotive industries, where high-precision threaded parts are crucial. It is also employed in the production of medical implants and devices, where exceptional accuracy and clean threads are necessary.

Its angle ranges between 5 to 20 degrees, allowing for effective cutting force distribution.

Relief Machining

Relief machining is used to remove material from a part to create a recess or cavity that is typically inaccessible by conventional end milling. This method is crucial for creating space for assembly, reducing weight, or improving the part’s mechanical properties.

Common in the creation of mold tools and die where cavities are required for the molding process. It is also used in the automotive and aerospace sectors for lightweight structures that require high strength and durability.

Keyway Cutting

Keyway cutting is a specialized form of milling used to cut internal and external keyways. This technique is crucial for creating the slots necessary for keyways which are integral parts of couplings, gears, and other components to fit onto a mating shaft and provide torque transmission between shafts and rotating components.

Keyway cutting is predominantly used in the mechanical engineering field to ensure the proper fitting of gears, pulleys, and drive shafts. Its precision is vital for machinery that requires high torque transmission capabilities without slippage.

The angles used are typically between 10 to 30 degrees to ensure clean cutting without excessive wear.

Tapered Undercutting

Tapered undercutting is utilized to machine tapers and undercuts inside a hole or at the end of a shaft. This method is essential for parts that require a conical profile to facilitate a proper fit or for weight reduction purposes.

This machining technique finds applications in automotive components like hub connections, prop shafts, and where tapered profiles are needed for stress distribution or assembly purposes.

The angle used ranges from 15 to 75 degrees depending on the taper requirements.

O-Ring Groove Cutting

O-Ring groove cutting is a precision machining process used to create a recessed channel on a component. This channel is designed to hold an O-ring, which is crucial for forming a tight seal in assemblies that must be fluid or air-tight.

This method is widely used in hydraulic and pneumatic systems, automotive engines, and various fluid-handling devices. The precision of the groove’s dimensions are critical as they ensure the O-ring functions correctly under varying pressures and temperatures.

Tool angles are generally kept at a standard 45 degrees unless specified otherwise for unique applications. The width and depth of the cut depend on the size of the O-ring. Standard dimensions range from 0.5 mm to several centimeters wide, depending on the size of the part and the O-ring.

What Metrics and Measurements Are Crucial in Undercut Machining?

Understanding the metrics and measurements critical to undercut machining is essential for achieving precision in manufactured parts where undercuts are necessary.

These measurements not only ensure the fit and function of the part but also influence the choice of tools and techniques used in the production process.

• Cutting Depth: The depth of the cut determines how deep the tool penetrates into the material, crucial for achieving the desired undercut profile.
• Tool Diameter: The diameter of the tool affects the radius of the undercut, impacting how the tool maneuvers within the part.
• Surface Finish: A critical metric, especially for components requiring high precision and smoothness in the undercut areas to ensure proper fit and function.
• Cutting Speed: The speed at which the tool moves through the material, which can affect the heat generated and the final surface quality.
• Feed Rate: The rate at which the cutting tool advances into the material, crucial for preventing tool wear and achieving efficient material removal.
• Tolerance Levels: The acceptable range of variation in the dimensions, which can significantly affect the assembly of parts.
• Material Removal Rate: How quickly material is removed from the workpiece, impacting production time and tool wear.
• Tool Offset: Adjustments made to the tool path to compensate for the specific tool geometry used in undercutting.
• Spindle Speed: The rotation speed of the spindle, which affects the cutting speed and finish.
• Chip Load: The amount of material removed by each tool tooth, which influences the tool’s life and the quality of the cut.

What Are the Key Applications of Undercut Machining?

Undercut machining finds applications across various industries due to its ability to produce complex geometries that are difficult to achieve with other machining processes. Here are ten industries where undercut machining is commonly used:

1. Aerospace: Fabrication of engine components, airframe structures, and landing gear parts that require precise undercuts to ensure aerodynamic performance and structural integrity.
2. Automotive: Production of engine parts, transmission components, and complex assemblies that require undercuts for weight reduction and assembly precision.
3. Medical Devices: Manufacturing of surgical instruments and implants where undercut features are necessary for ergonomic design and functionality.
4. Electronics: Creation of connectors, housings, and mechanical components for consumer electronics where compact and complex shapes are required.
5. Tool and Die Making: Development of molds and dies that have undercut regions to create specific part features in casting and molding.
6. Consumer Goods: Items such as toys, household appliances, and sports equipment that require innovative designs facilitated by undercut machining.
7. Oil and Gas: Components such as valves, pistons, and connectors that require undercuts for operational efficiency and safety in harsh environments.
8. Marine: Parts for boats and underwater equipment where undercuts provide unique geometries for fluid flow and structural connections.
9. Jewelry and Crafts: Detailed designs and patterns that require fine undercutting for aesthetic purposes in materials like metals and gemstones.
10. Defense: Manufacture of complex military equipment and components where undercuts are necessary for assembly, lightweighting, and integration of multifunctional features.

What are the Main Design Considerations in Undercut Machining?

When planning for undercut machining, it is vital to integrate several design considerations to enhance efficiency and precision. Here are key aspects to keep in mind:

• Tool Accessibility: Ensure that the tools can reach all areas where undercuts are necessary without interference.
• Component Geometry: Design parts with geometries that allow for easy removal from the mold, considering the undercut locations and depths.
• Material Selection: Choose materials that can withstand the stress of machining without deforming or breaking, especially in undercut areas.
• Tolerances: Set precise tolerances to ensure that the parts fit together well in final assembly, especially when undercuts are involved.

Material Properties Influencing Undercut Machining:

• Hardness: Harder materials may require more specialized tools or slower machining speeds to achieve clean undercuts.
• Elasticity: Materials with high elasticity might deform during the machining process, affecting the accuracy of the undercut.
• Thermal Stability: Materials that can withstand high temperatures are preferable, as machining can generate significant heat.
• Corrosion Resistance: Consider materials that resist corrosion to ensure the longevity of the undercut features, especially if exposed to harsh environments.

What Are the Costs Associated with Undercut Machining?

Understanding the cost implications of undercut machining is crucial for budgeting and deciding on the feasibility of using this method for specific projects.

Cost Factors:

• Tool Costs: Specialty tools required for undercutting, such as lollipop cutters and dovetail cutters, can be more expensive than standard tools.
• Machinery Costs: Advanced CNC machines capable of multi-axis movements necessary for producing undercuts can represent a significant investment.
• Labor Costs: Skilled machinists are required to program and operate machines for complex undercutting tasks, leading to higher labor costs.
• Material Waste: Materials wasted during the machining process, especially if the undercuts lead to a higher rate of scrap.

How Cost-Effective Is Undercut Machining Compared to Other Methods?

Evaluating the cost-effectiveness of undercut machining involves comparing it with alternative methods like molding or casting, where undercuts can be integrated without additional machining.

Comparison Points:

• Setup Time: Undercut machining might involve longer setup times due to the complexity of tool paths compared to standard machining processes.
• Production Speed: Although slower, undercut machining may still be faster than creating molds for certain complex parts.
• Flexibility: Undercut machining offers high flexibility for design changes compared to mold-based manufacturing methods.
• Quality and Precision: Machining often provides higher precision and better surface finish, which can justify the higher costs in scenarios where these characteristics are critical.

What are the 8 Best Practices for Efficient Undercut Machining?

Whether you are working with CNC machining or other forms of tooling, adopting the best practices ensures that you get the most out of your efforts. Here, we delve into tips and techniques to optimize undercut machining.

Selecting the Right Tool

Choosing the correct tool is the first step towards efficient undercut machining. The right tool ensures precise cuts and minimizes the chances of tool breakage. Different tools like slot cutters, lollipop cutters, and T-slot cutters serve various purposes, and selecting the appropriate one is essential.

• Slot Cutters: Ideal for creating narrow slots.
• Lollipop Cutters: Suitable for curved and spherical undercuts.
• T-Slot Cutters: Best for T-shaped grooves.

Shallow Cuts

Making shallow cuts can significantly enhance the efficiency of your machining process. Shallow cuts reduce the stress on the cutting tool, extend its lifespan, and improve the overall surface finish of the machined part.

Secure the Workpiece

Securing the workpiece firmly ensures stability during machining, which is critical for achieving precision. Use appropriate clamping methods and fixtures to hold the workpiece in place, preventing any unwanted movement that could lead to errors.

Avoid the Need for a Custom Tool

Whenever possible, try to use standard tools. Custom tools can be expensive and time-consuming to manufacture. Standard tools are readily available and can be used effectively with proper planning and setup.

Use Quality Cutting Tools

Invest in high-quality cutting tools. The initial cost may be higher, but the benefits of using durable, reliable tools include better performance, longer tool life, and improved quality of the machined parts.

Eliminate Undercuts If Possible

If the design allows, eliminate the need for undercuts. This simplification can reduce machining time and costs. Review the design to see if adjustments can be made to avoid undercuts without compromising functionality.

Implement Effective Machining Strategies

Adopt efficient machining strategies to improve productivity. This includes using CAM software for precise toolpath generation and optimizing machining parameters like speed, feed rate, and depth of cut.

Partner with Experts

When more complex and precise operations are needed, like undercut machining, partnering with experts can significantly improve the efficiency and quality of your machining projects.

For instance, 3ERP is a leading provider of custom CNC machining services to engineers, product developers, and designers.

Our experienced engineers have built up rich experience from various CNC machining projects in numerous industries. We can handle tight tolerance CNC machined parts with complex geometries. 3ERP offers consistent, high-quality CNC parts that are fully inspected by their quality control department to ensure parts are built to specification and free of defects. They have enough capacity to offer fast turnaround CNC machining services by using in-house facilities and their qualified manufacturing network.

Conclusion

Undercut machining isn’t a straightforward machining method, due to its intricate geometry, making it complex for those with zero knowledge on CNC machining. However, its usefulness in the manufacturing world makes it an essentiality, as it aids in the creation of complex parts that other machining methods cannot achieve.

To get the perfect undercut, you just need the right tool and proper observation of the entire manufacturing process. So, to ensure maximum functionality of components and high quality of aerospace parts, medical parts or consumer electronics, consider the undercut machining.

Frequently Asked Questions

1. What is the difference between undercut and overcut machining?

Undercut machining involves creating a recess or groove that is not directly accessible from the outside, often requiring specialized tools like lollipop cutters or T-slot cutters. Overcut machining, on the other hand, refers to a situation where material is removed beyond the intended cut line, usually due to tool deflection or improper setup. Both terms are critical in ensuring precision in CNC machining processes.

2. What is the difference between undercut and notch?

An undercut is a recess or groove that restricts the removal of a part from a mold or fixture, often requiring specialized tools for machining. A notch, however, is a simpler cut or indentation made on the edge or surface of a part for purposes like alignment, locking, or stress relief. While both involve material removal, undercuts are typically more complex than notches.

3. What are the differences between undercut machining and standard machining processes?

Undercut machining requires specialized tools and techniques to create recesses or grooves that are not directly accessible, such as using lollipop cutters or T-slot tools. Standard machining processes involve more straightforward cutting, drilling, or milling operations that do not require these specialized tools. Undercut machining is often necessary for parts with complex geometries, whereas standard machining is used for simpler shapes.

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