How to Add Chamfers and Fillets in Your Design 

Designing a part is rarely just about making something look good on a screen. I often remind clients: when your digital design meets a real CNC machine, you’ll quickly learn what works and what doesn’t. 

Last winter, I worked with a medtech startup whose lead engineer sent over an enclosure model full of sharp pockets, square notches, and perfectly crisp corners. The concept was clever, but I immediately saw a challenge—none of the internal corners could actually be cut with standard tools.
I called them up.
He admitted, “Honestly, we didn’t think much about how the machine would handle these.”
I walked them through the difference between what you can draw and what a 6mm end mill can cut. We went over each edge, talking about which ones handled stress, which would be handled daily, and which were purely visual. In the end, they replaced almost every inside corner with a fillet. They also added generous chamfers to every interface where users would swap batteries or connect cables.
Their mechanical lead told me weeks later:

“You saved us days of back-and-forth with the shop. The first prototypes just felt right in the hand—no more weird stress marks, no painful edges. I wish we’d started with these details in mind.”

The story repeats itself with teams from all kinds of industries. I once helped a robotics company whose assembly team kept complaining about brackets that required force to fit together. It was a classic issue—perfect CAD fits with zero lead-in. We introduced a simple 1mm chamfer on the leading edges. Suddenly, assembly time dropped by half, and nobody cut their hands on the raw metal. 

What stands out from all these experiences is that fillets and chamfers are rarely the star of the design—but they’re often the difference between a part that causes headaches and one that just works.
When you design with these features in mind, you don’t just reduce machining cost or time. You build resilience into your product. You protect your users, your assemblers, and your brand from the avoidable problems that come from ignoring the realities of physics and human touch.

Engineers sometimes ask, “How do I know if I’m using the right size fillet?”
My honest answer: there’s rarely a one-size-fits-all. I always suggest starting with tool radii your CNC partner keeps in stock—common values like 0.5mm, 1mm, or 2mm. For high-stress areas, bigger is usually better. For appearance, ask yourself who will touch it, where it might get bumped, and if cleaning or coating matters.

As for chamfers, think about where parts meet or slide together. Even a 0.5mm chamfer can be the difference between frustration and effortless assembly.

I still remember a customer who wrote:

“I used to think those tiny details didn’t matter. Then I got my first batch of prototypes back, and I realized the parts that had fillets looked and felt more expensive. And they lasted longer in testing.”

Why do machinists always talk about tool radius?
Because every end mill is round—if you specify a perfect inside corner, it means the machine needs to take extra steps, change tools, or even create weak spots in your part. Fillets that match tool size make machining smooth and efficient.

Can fillets really prevent cracks and failures?
Absolutely. Sharp transitions concentrate stress, especially in metals and plastics under repeated loads. Even a small fillet spreads out the force and dramatically increases fatigue life.

Do chamfers help with assembly, or just make parts look better?
Both. Chamfers remove burrs and sharp edges, but their biggest value is making parts slide or “find their way” together. You’ll notice it most when you’re assembling something by hand—or getting complaints from people who do.

Is there a downside to too many small fillets and chamfers?
Yes. If you specify a dozen custom sizes, it can slow down machining and inspection. Stick with a few standard values unless you have a critical reason not to.

Real-World Tools for Designers

If you’re not sure how to implement these details, most CAD software makes it simple. Tools like SolidWorks, Fusion 360, and Siemens NX have fillet and chamfer features that let you preview and standardize every edge. If you want to see how your choices affect manufacturability, try uploading your CAD file to an instant CNC quoting tool—many will flag unrealistic edges and suggest best practices.
For custom advice, reach out to a real machinist or supplier. I often review models for clients and point out where a small tweak can save days and dollars.

If you’re wrestling with your own corners or want a gut check before you send your next file out for quote, our team is always ready for a conversation. We believe the smartest solutions are always a little collaborative—and that the right advice, at the right time, is worth more than any software trick. 

About Our Team

We are a close-knit group of engineers, machinists, and manufacturing specialists who live for solving real-world design problems. With a background that spans medical devices, robotics, industrial automation, and hands-on product development, we focus on making great ideas work beyond the CAD screen. We don’t just “take orders”—we coach, review, and sometimes challenge you to make sure the end result is something you can be proud of.
We care about the little things because they add up to big outcomes: stronger parts, smoother assembly, better user feedback, and fewer surprises after launch.
Whenever you need a second opinion, real feedback, or a partner to bridge the gap between design and manufacturing, we’re here—and happy to help.