A lot of people have heard the terms “fillet” and “chamfer”, and they might use them interchangeably. The truth is that these features are very different, and they can dramatically change the function of your parts.
In this guide, we’ll explain the real difference between a fillet and chamfer. We’ll tell you which option is better for you, and explain the specifics of both.
What Is a Fillet?
A fillet in engineering is different than a filet mignon you would order at a restaurant. For one, a fillet has an extra L and it’s pronounced “fill it”, as opposed to “fillay” with one fewer L.
A fillet is a rounded corner on a part. You’ll typically see it as a callout on an engineering design, but you can notice it in-person. It’s identical to a “bevel” on a screen or countertop. If you have a case on your phone, there’s a good chance there’s a fillet on every corner.
You might also see a fillet used in welding. Naturally, a welding line will leave behind a bubbled, convex bead as welding is done. This is called a “convex fillet”, or just a “fillet weld” in general.
In practice, a fillet is used to round corners and make them safer to touch. When a machinist is done machining a 90-degree angle on a piece of metal, it can slice your hand open very easily. If they add a fillet to the corner instead, it will be smooth and safe to touch.
What Is a Chamfer?
A chamber falls into a similar category as a fillet. It’s also a machining step that’s done after making a part, but a chamfer is an angled cut as opposed to the rounded edge of a fillet.
The most common place to see a chamfer is on a nut. The surface right below either flat face typically has some sort of chamfer.
A chamfer can be added to avoid having too much stress on the corners of a part. Adding a chamfer can actually avoid deformation.
You might also add a chamfer to drilled holes to help bolts slide in easier.
Why the Difference Matters
Now that you know what a fillet and chamfer are, let’s discuss their differences. More importantly, we’ll figure out why the difference between a fillet and chamfer is so important.
Inside Versus Outside
A fillet can be added to the inside or outside of a part with ease. A chamfer can be added easily to the outside of a part, but it’s more difficult to do inside a part.
In fact, fillets are made by default when you use traditional machining. When we run a CNC mill, the bit has a radius to it which makes it impossible to make truly square corners on inside cuts. Instead, you’re left with a fillet that has the same radius as the tool bit.
If you don’t want fillets inside your part, you would need to specifically ask for it. This request can be very tricky, and could potentially add a lot to the final quoted price. With that said, it’s better to accept a fillet whenever the application allows for it, and only specify a lack of a fillet when it really matters.
How to Callout the Feature
On an engineering drawing, a fillet and chamfer can both be called out using a line and some symbols. A fillet uses a radius to specify the size of the fillet, and a chamfer uses an angle and length of the face. Alternatively, you could dimension the cutout length and height and provide an angle.
How They’re Made
If you just need a general fillet made on your parts, then they’re made by running a CNC mill and getting the angle by default. However, it gets a lot trickier if you need a specific radius for any reason. Then, we need to use a special cutting tool with your specific radius.
To make a chamfer, we can use the same cutting tool regardless of the angle. It’s a lot easier and more versatile to machine a chamfer.
Cost and Machining Time
Since they’re harder to make, fillets are more expensive to make. The price difference might not be very noticeable, but it’s worth mentioning.
In fact, cutting a fillet doesn’t take us too much time — unless you have a lot of non-standard fillet sizes that vary across the part. Then the time starts to add up.
Cutting chamfers is a little less expensive and faster to do.
Maybe it’s just personal preference, but a lot of people like the look of a fillet over a chamfer. A fillet is rounder, more appealing, and makes the part flow. A chamfer can definitely look good, but it results in a number of edges and different angles.
If you want to think about vehicles, a chamfer will look like a Tesla Cybertruck, and a fillet will look like a Porsche 911.
Getting the Right Fit
A chamfer helps you get the right fit when you have shafts going into holes. If the hole has a chamfer on it, then you have a nice angle that helps the pin get inserted. Using a fillet doesn’t have the same impact.
Fillets are safer to have on parts for the same reasons we mentioned earlier: the rounded surface is safer on the skin than a sharp angle. Chamfers are safer than raw, unfinished machine surfaces, but not as safe as fillets. You can still cut your hand on a chamfer, especially if it’s at a sharp angle.
Knowing the difference between a fillet and chamfer should help with all of your engineering designs moving forward. If you want to learn more or get started, you can reach out to our team at Rapid Axis. We are a full-service machine shop that handles machining, 3D printing, finishing, and much more. Get a free quote today.