CNC Machining Design

How chamfers and fillets impact machining costs

By May 19, 2021
Chamfers and Fillets Hero

Most product designers and engineers know to never cut corners during the component creation process, especially when it comes to designing corners. Besides a sharp corner, which is the conventional geometry between two joining surfaces or vertices, you can choose to design corners as either chamfers or fillets. A chamfered edge is sloped or angled, reducing the impact of sharp corners and improving the fit of mated parts. A fillet design entails a rounded edge, which eliminates all sharp corners and contributes to a component’s look and longevity.

Both chamfers and fillets offer some key advantages, particularly when it comes to adding strength to part corners by reducing stress concentration. However, including fillets and chamfers in your designs may incur additional CNC machining costs and can sometimes slow production. It’s important to weigh these factors and others before deciding whether or not to include chamfers and fillets in your part designs.

Comparing the advantages of chamfers and fillets

Thanks to their rounded edges, fillets can help improve a part’s assembly with mated parts. Fillets also have lower stress concentration factors, because they help distribute physical stress over a broader area. As such, fillets can withstand larger loads with ease.

Fillets are often as durable as they are safe, since smooth edges remove sharp corners that could cause damage. The smooth edges produced by fillets also allow for easier coating and painting, whereas the angles of a chamfer will cause coatings to peel back over time.

chamfers and fillets silver tray
Both chamfers and fillets offer some key advantages, particularly when it comes to adding strength to part corners by reducing stress concentration.

Although chamfered corners are more prone to natural wear due to their sharp edges, these edges are hidden and therefore far safer than edge corners. Chamfers are also more forgiving than fillets when it comes to fitting mated parts together — they are particularly well-suited for enabling easy entry of a male part into a female part during assembly, since chamfered holes allow for smooth movement and insertion. What’s more, chamfers are fast and easy to apply, as one single tool can create chamfers of various sizes.

Considerations when using chamfers and fillets

There are a number of considerations you should weigh before determining whether to include chamfers or fillets in your product design. Here are five key factors to assess:

1. Functionality

Keep a product’s end use in mind. Is its environment likely to cause damage if the corners are sharp? Will the part be used in load bearing applications, and if so, how much weight must the part support? Consider whether the product’s function relies on the presence of a chamfer or fillet. For example, will the part need to be plated with paint or another coating, and will that varnish require long-term wear? Will the component need to fit with a mated part exactly, or can there be some leeway? Answering these questions will help determine which kind of corner you should utilize.

2. Location (internal vs. external)

It’s crucial to factor in whether the corner you’re designing is positioned inside or outside the component. In most cases, external edges are far more important to fully consider because they are both more visible and more susceptible to external conditions and wear over time.

However, when designing a hole to fit with a shaft, it’s also vital to consider chamfering or filleting internal corners. Chamfering around the edges of a hole is a recommended practice, since chamfered holes contribute to easier pin movement and fastener insertion.

3. Tolerances

Optimizing dimensional tolerances is a crucial part of product design, especially when it comes to mating parts. Determine how precise your product needs to be and how a mismeasurement could affect the product’s function and fit. Additionally, ask yourself how important tolerances are to ensuring the performance of the part, and consider how tolerances will be checked. Keep in mind that extremely tight tolerances can be expensive to apply, and chamfers often allow more margin for error.

4. Cost

Applying chamfers and fillets can be expensive. Take the time to consider whether or not filleting or chamfering is critical to the part’s success, or if it would merely serve as an added benefit. If you truly need a specialized corner, consider how many components you’ll have to produce as this will also affect costs. Although it’s often necessary to apply chamfers and fillets to a component’s design, be sure that you’re absolutely positive before spending time, money, and resources on manufacturing tools.

5. Other considerations

Finally, consider other factors such as timeline and aesthetics. How large is your production run, and are you likely to require additional parts beyond the first run? How quickly will you need your parts? What aesthetic requirements must you meet? Will your part be used in consumer goods, and if so, what kind of user experience would you like to create? Is finishing or post-processing of any sort needed? Use these questions to further guide your decision process between chamfers vs. fillet

How chamfers and fillets impact machining costs

Manufacturing specialized corners usually comes at an additional financial cost. As a general rule, it is less expensive to manufacture chamfers. This is because one single tool can create chamfers of all different sizes, simplifying production and saving time and resources.

While the costs of utilizing specialized tools can add up fast — especially when applying fillets of various sizes — these up-front expenses could prove cost-effective in the long run. Using fillets can prevent the need for intermittent recoating or repainting, and there’s a decreased risk of failing inspections from the sharp corners created by chamfers. When determining the manufacturing costs of fillets and chamfers, it’s important to balance up-front spending with the potential to lower expenses in large volume production.

A more efficient way to incorporate chamfers and fillets with Fast Radius

When designing the corners of your components, it’s important to choose between fillets or chamfers based on factors including part application and requirements, aesthetics, and production costs. Chamfers are easier to manufacture and increase allowance for mated parts, but can present more risks and performance issues due to their sharp corners. Fillets are expensive to manufacture but generally safer and longer-lasting, as they provide smooth surfaces that prevent injury and withstand degradation. Both design features reduce stress concentration and can bring visually striking features to your design.

At Fast Radius, we don’t cut corners when it comes to your component’s corners. Our design advisory services will help you make the right call between applying chamfers or fillets, and we consider every aspect of the production process with the utmost engineering expertise. Fast Radius now offers in-house CNC machining — in addition to a suite of other services including 3D printing, injection molding, and urethane casting — allowing us to provide you with end-to-end oversight on all of your on-demand manufacturing projects. Contact us today to get started on your next project.

Visit the Fast Radius resource center for more information on saving money with CNC machining and mitigating stress concentration through careful product design.

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