by hearingearly hearingearly

Fillets and chamfers are two ways to design the edges where two surfaces of a part meet. Both fillets and chamfers are used to ease sharp edges and corners. A chamfer replaces the sharp change in direction with an angled slope, while a fillet makes a smooth curve to join two surfaces. Fillets reduce stress concentration at corners or changes of sections because they transmit applied stresses across larger surface areas. While fillets are more difficult to manufacture than chamfers, they reduce overall stress concentration throughout the corner region more than chamfers and therefore result in more durable parts. However, chamfers offer the advantage of easier manufacture and assembly of mating parts. This article will describe the differences between fillets and chamfers, and the application of each.

What Is a Fillet?

A fillet is an interior or exterior edge that has been rounded. Fillets are helpful in improving the mechanical properties of load-bearing parts produced by casting, machining, molding, and 3D printing. For casting, fillets help increase the manufacturability of cast parts because it helps in the removal of the part after molding. The smooth, rounded edges allow the part to easily slide out as opposed to sharp edges. 

While fillets can be produced directly in 3D-printed parts, fillets are produced by a radial tool path that connects two non-parallel surfaces and an appropriately sized end mill in machining, casting, and molding. The cost of producing a fillet is influenced by the size of its radius and the edge length. During machining, end mills require clearance to turn and form the corners of a part. It is recommended that the fillet radius does not match the radius of the tool, as the tool will need to come to a complete stop and turn 90 degrees before turning if the radii match. This slows the machining process and adds cost. Instead, manufacturers should start cutting the fillet with an endmill smaller than the radius of the fillet and slowly increase the size of the endmill until the entire fillet is cut. 

What Is the Purpose of a Fillet? 

Fillets reduce stress concentrations in changes of section and direction on a part. They increase the part’s load-bearing capacity and fatigue life. Fillets accomplish this by distributing stresses over a larger area. Fillets are more effective than chamfers at reducing stress concentrations. This is because stress concentrations in chamfers are focused on the edges of the chamfer where the two surfaces meet. Beyond their mechanical benefits, fillets can improve the aesthetics of a part by removing the harsh appearance of sharp edges and corners.

How Does the Fillet Edge Look Like?

Fillets appear as concave rounded edges for interior corners and as convex rounded edges for exterior corners. The rounded edges blend smoothly with the connecting surfaces in every direction, producing a seamless appearance.

How Are Fillets Designed in AutoCAD®?

Making a fillet in AutoCAD® is done by using the “FILLET” command. Select two lines in your design that meet at an interior or exterior corner. Enter the size of the radius that will form the fillet. Once a value has been prescribed, AutoCAD® will automatically adjust the length of the selected lines, generate the fillet, and remove the sharp corner.

Does a Filleted Edge Look More Appealing?

Yes, filleted edges look more appealing. Fillets can be desired for interior surfaces because they create a seamless surface that is blended together. They may be desired for exterior surfaces because they remove potentially dangerous sharp corners and burrs.

What Is a Chamfer?

A chamfer is an angled or sloped edge between two connecting surfaces of a part. Chamfers, like fillets, help improve the mechanical performance and aesthetic qualities of a part. While chamfers can help reduce stress concentrations, they do not distribute stress as well as fillets do. This makes them less suitable for parts that experience high stresses. Chamfers are more often used to aid in the part assembly since the sharp edges allow parts to mate more easily by allowing them to self-locate. Most chamfers connect two surfaces at a 45-degree angle, but a chamfer can be made at any angle. 

What Is the Purpose of a Chamfer?

The primary purpose of a chamfer is to ease sharp edges from a part. It allows parts in an assembly to fit together easily. The angled edges allow male and female parts to slide against each other as they are assembled. It is easy to manufacture chamfers because the required tool does not have to cut a radius and instead cuts a flat surface between two adjacent surfaces. Different sizes of chamfers can be created with a single chamfer tool, countersink, or spot drill. This helps to make the fabrication of chamfers cost-effective.

What Does a Chamfered Edge Look Like?

A chamfer looks like an angle or ramp that connects two surfaces. Chamfers are often made at 45 degrees from the point where the two surfaces meet but chamfers also can be specified based on the leg lengths of a right triangle. Additionally, designers can specify the angle or the length of the face of the chamfer (the hypotenuse of the right triangle). Figure 1 is an example of a chamfered part:

Fillet vs. Chamfer — What Are the Differences and Uses?