Design and processing principles for fillets and chamfers in custom CNC parts

• Design and processing principles for fillets and chamfers in custom CNC parts
  • Why use rounded corners?
  • Why use chamfering?
  • Which parts require chamfering and filleting?
  • Issues to consider before designing chamfers and fillets for parts
  • Basic rules for designing fillets or chamfers on CNC parts
  • CNC part fillet design principle
  • CNC Part Chamfering Design Principles
  • When should you choose a rounded or chamfered design?
  • How do fillets and chamfers affect processing costs?
  • Create fillets and chamfers for your CNC part projects using Elimold.
  • Summarize

In product design, details often determine success or failure. Edge and corner finishing, a seemingly minor design element, actually plays a crucial role. The most common edge and corner finishing techniques are rounded corner finishing and chamfering finishing.

Rounded corners and chamfers are fundamental design elements in product design. Compared to sharp corners, rounded corners and chamfers make the product easier to use and assemble , create a smoother visual effect, and better showcase the product’s simplicity and aesthetics. Furthermore, creative use of rounded corners and chamfers can make a product stand out.

Therefore, understanding the differences between these two design concepts and how to handle them in the CNC machining process is crucial. In this article, we will delve into the design of fillets and chamfers for CNC machined parts . Read on to learn how to handle them in your designs.

Why use rounded corners?

The rounded shape of rounded corners makes them suitable for various applications in CNC machining. For example :

Stress distribution	Unlike sharp corners that concentrate stress in one area, the rounded shape of rounded corners can distribute stress evenly over a larger area. This enhances the overall strength and fatigue resistance of CNC parts.
Improve processability	By using larger diameter cutting tools, it is easier to machine rounded corners than sharp corners, and tool breakage is less likely to occur.
Enhance aesthetics	Rounded corners can also improve the aesthetics of parts by creating a smooth transition between surfaces. When done properly, rounded corners can provide a beautiful and refined appearance.
Improve coating adhesion	The smoother, more consistent surface provided by rounded corners allows for better coating adhesion on parts that require painting or coating treatments. Overall, this results in higher quality and more aesthetically pleasing products.

Why use chamfering?

The chamfering design and characteristics of CNC parts give them a variety of applications in product design . For example:

Deburring	Chamfering is an effective tool for removing sharp edges left after the machining process. Manufacturers use chamfering to remove burrs, sharp protrusions, and other defects.
Reduce the risk of damage	Chamfering helps prevent edge damage to CNC parts during handling, transportation, or installation. By chamfering the edges, the likelihood of chipping, denting, or other forms of damage to the parts’ edges can be reduced, thus ensuring the integrity of the parts.
Simplify assembly	Chamfers provide beveled edges, making it easier to align and fit components during assembly. This is especially important when fasteners such as screws or pins need to be accommodated.
Reduce stress	Similar to fillets, the slightly beveled edges of chamfers result in a larger stress distribution area than sharp corners. This helps reduce the risk of CNC parts cracking or breaking under pressure.

Which parts require chamfering and filleting?

The design of chamfers and rounded corners is primarily for safety, process considerations, and aesthetic purposes. After CNC machining, parts often have very sharp edges and corners. Chamfers and rounded corners are commonly used to remove sharp corners and burrs, preventing scratches. In these areas, chamfering and rounding can also relieve stress at sharp points, reducing damage and failure caused by impacts and fatigue.

Some parts require appropriate chamfers and fillets due to manufacturing processes. This is because many parts need to be integrated with the overall design of CNC machined components, and chamfering facilitates assembly. Some chamfering equipment can also prevent deformation caused by heat treatment and prevent defects from impacts, thus avoiding impacts on part quality. Therefore, designing chamfers or fillets at product corners will affect the final quality of the product.

In addition, chamfers and rounded corners also serve a decorative purpose. Rounded chamfers can make a product appear more approachable, friendly, and attractive. When the chamfer radius is small, it creates a sharp yet refined “line,” showcasing the product’s exquisite craftsmanship and overall aesthetic.

Issues to consider before designing chamfers and fillets for parts

While chamfers and fillets are aesthetically pleasing and easy to design, they increase machining time and production costs. Machining design requires an understanding of how parts are manufactured and the skill to adjust designs to maintain low production costs. With that in mind, before adding chamfers or fillets to your design, you should ask yourself the following questions:

• What is the purpose of chamfering or rounding?

• Is the chamfer or fillet necessary for the part to function?

• Given the planned production volume, is it cost-effective to increase this design?

• How to check tolerances?

Basic rules for designing fillets or chamfers on CNC parts

In standard machining, vertical inner and outer fillets can be easily machined, while inner chamfers cannot. Fillets require specific tools to achieve different radius sizes (in machining , it is good practice to have a fillet radius larger than the tool radius). In contrast, chamfers do not require specific tool sizes; different chamfer sizes can be machined by controlling the depth of cut.

Both fillets and chamfers can reduce stress concentration and optimize flowability. However, fillets provide a continuous transition, while chamfers provide a linear transition, leaving an edge after chamfering. Compared to chamfers, fillets have lower stress concentration and less flow resistance, making them more popular in plastic parts unless the chamfered edges are further rounded.

However, if your design involves screw holes, locating holes, or locating pins, using fillets is not a good choice. Compared to fillets, chamfers have smaller, sharper edges, which helps them move more smoothly in the holes and makes assembly easier.

From an aesthetic perspective, fish fillets are often prioritized in industrial design due to their visually pleasing characteristics. Rounded corners are soft and comfortable, conveying a sense of security and approachability. In contrast, chamfers can feel sharp and aggressive. Large chamfers are rarely used in consumer goods, but they can create a unique look in certain details, serving as a finishing touch.

Depending on the overall design requirements of the CNC part , fillets and chamfers can be used on the outer edges. If appearance is not important, such as in machined metal parts, a simple chamfer can be chosen to soften sharp edges, thus reducing part costs. On the other hand, if aesthetics are important and fillets are required, the radius of the inner fillets must be considered. If the radius is too small, you may need to perform more expensive and time-consuming machining.

CNC part fillet design principle

To maintain uniform wall thickness in CNC parts, the outer radius *r* at corners should generally be equal to the inner radius *r* plus the wall thickness *m*. A minimum inner radius of 0.5 mm is recommended. For chamfers, to maintain absolutely uniform wall thickness, the outer chamfer should be offset from the wall thickness *r* to form the inner chamfer.

Furthermore, for internal structural features such as ribs, screw holes, and clips connecting to the main wall, rounding should be carefully considered. Rounding these areas will cause localized thickening of the material, resulting in surface dents. If rounding is necessary to ensure strength, the material should be thinned before rounding. For example, a typical method of reducing material in threaded holes is to create a “crater” shape.

CNC Part Chamfering Design Principles

Similar to fillets or arcs, chamfers can be used to soften sharp edges or create a transition between two vertical surfaces. From the perspectives of reducing stress concentration and optimizing flow angles, fillets are superior to chamfers. However, chamfers offer additional functionality, such as facilitating manual positioning of parts during assembly. Chamfers can also be used for aesthetic design: where most parts are rounded, chamfered edges are more easily distinguishable. As with fillets, it is recommended to maintain a consistent wall thickness; therefore, chamfers on outer edges should be applied simultaneously at inner corners.

When should you choose a rounded or chamfered design?

Ultimately, your choice between using rounded corners or chamfers should depend on your specific needs. But generally speaking:

Design rounded corners in the following situations

• Parts that require a smooth surface

• Parts requiring rust prevention

• Areas subjected to high stress

• Parts requiring additional coating or paint adhesion

Design chamfers in the following situations

• Parts with hidden features (and where aesthetics are not important).

• Parts requiring good assembly clearance

• Cost-sensitive projects

• Parts with simple edge transitions

How do fillets and chamfers affect processing costs?

Choosing between rounded corners and chamfered edges will significantly impact your overall machining budget. Here’s why:

Rounded corners	chamfer
Higher cost: Due to its curved nature, fillets require more complex toolpaths and may require the use of multiple tools with different radii to achieve the desired shape. This means longer machining time and higher costs.	Lower cost: Chamfers have straight edges and can be machined using single tools of various sizes. This simplifies toolpaths and reduces machining time, thereby lowering production costs.
3D milling: Creating rounded corners often requires 3D milling, which is a more time-consuming process compared to the simpler machining techniques used for chamfering.	Faster production speed: Its simple geometry allows for faster processing speeds, further saving costs.

Create fillets and chamfers for your CNC part projects using Elimold.

Our engineering team, with years of experience in design engineering and parts manufacturing, will help you choose the right approach for your machined parts, so you can be confident that your design will be transformed into a physical product exactly according to your requirements and specifications. Submit your documents and start your project with us. We offer services including CNC turning, 3, 4, and 5-axis milling. Partner with Elimold, and we will reward you with the best results at competitive prices. We also offer a range of secondary machining options, packaging, assembly, and shipping to meet your diverse needs.

Summarize

in CNC part design lies in understanding their differences and when to use them. However, we understand that this topic isn’t easy for everyone to grasp. Therefore, if you’re still unsure how to handle fillets and chamfers, feel free to consult an expert. They will provide the best advice based on your CNC machining requirements.