Difference Between a Fillet and Chamfer

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Difference Between a Fillet and Chamfer

“What is a fillet, and what is a chamfer?” You probably wondering what’s the answer for this question, especially you are working on mechanical engineering drawing for some custom mechanical parts. 

It is very important to know the difference between a fillet and a chamfer. A fillet is the rounded edge of an object. A chamfer is the end of an object that has been cut off at an angle.

1) Fillet: The rounded edge of an object

2) Chamfer: The end of an object that has been cut off at an angle

fillet and chamfer

What is a Fillet?

In mechanical engineering, a fillet is a rounding of an interior or exterior corner of a part design. An interior or exterior corner, with an angle or type of bevel, is called a “chamfer”. Fillet geometry, when on an interior corner is a line of concave function, whereas a fillet on an exterior corner is a line of convex function (in these cases, fillets are typically referred to as rounds). Fillets commonly appear on welded, soldered, or brazed joints.

three types of fillet mechanics


There are three types of fillet mechanics: miter, concave, and convex fillets. On the interior side, fillets are concave, while on the exterior, they are convex. Engineers use fillets to reduce the stress on a part. The fillet is a common engineering feature that is used to create rounded corners. The purpose of the fillet is to reduce stress concentration at the corner of a part.

What is a Chamfer?

Chamfering refers to the process of cutting the edges and corners of the workpiece into a certain slope. Chamfering is to remove the burrs on the parts due to machining, and also to facilitate the assembly of the parts, generally make chamfers at the ends of the parts.

what does chamfer look like

Chamfering is a term in mechanical engineering. For example, a hole is drilled on a piece of wood, and the hole wall and the board surface are at a 90-degree right angle after completion. Chamfering is to make a 45-degree facet on the 90-degree edge. , so that the plane and the inner wall, or the board surface are all 45 degrees.

When you are wondering does a chamfer have to be 45 degrees? You need to know in the process of mechanical design and manufacturing, chamfers are devided into two different types: 45-degree chamfering and non-45-degree chamfering. Among them, 2*45 degrees is a common form of chamfering of 45 degrees, and 30 degrees and 60 degrees are common angles for non-45-degree chamfering, which have 2*30 degrees and 3*60 degrees. 

When Do You Need a Fillet or Chamfer?

When Do You Need a Fillet or Chamfer?

Design chamfers and rounded corners are mainly for safety, craftsmanship, and appearance decoration needs.

After the parts are processed by milling, the corners are often sharp, and chamfering and rounding are often used to remove sharp corners and burrs to avoid scratches. Chamfering and rounding in these places can also remove the stress of the tip of the product, reducing the damage and failure of the product caused by bumps and fatigue.

However, some parts must be designed with appropriate chamfers and fillets due to process requirements. The chamfering of the shaft hole matching parts is easy to assemble; the chamfering of the gear tooth tip can not only prevent the tooth tip from being warped due to heat treatment deformation, but also prevent the tooth tip from being hardened and collapsed, so as to avoid affecting the meshing quality.

The draft angle design of powder metallurgy parts can facilitate product demoulding and reduce wear; the chamfering or rounded corners are designed at the corners of the product structure to facilitate smooth liquid flow in the mold, uniform pressure and easy demoulding.

Chamfered and rounded corners are also decorative. The rounded chamfer makes the product more friendly and attractive.

The transition part of the rounded corner is smooth without sharp points and edges; while the chamfered corner forms a bevel, and no matter how the inclination angle changes, the two sides of the bevel will form sharp corners with the contour of the part, but these sharp corners The angle is obtuse, not sharp. Therefore, the fillet is more suitable for reducing stress concentration than the chamfer, and the protective performance of the fillet is better than that of the chamfer. In the assembly relationship, the chamfer design often plays an import role, which is convenient for assembly, but it is necessary to avoid interference.

In machining, both rounding and chamfering can be done by cutting, grinding and other processing methods, but the processing range of chamfering is wider than that of rounding, and it is easier to process.

For example, when machining a shaft part, when using an ordinary lathe, the chamfering can be completed with an ordinary turning tool, while the rounding needs to use a special forming tool; when using a CNC machine tool, the processing efficiency of the chamfering is higher than that of the rounding.

Fillet VS Chamfer
PurposeThe chamfer of the orifice plays the role of introduction, and the outer surface is mostly chamferedAvoid sharp edges hurting people, use rounded corners on the inner surface
TimingShort machining timingLong machining timing
Tools1 tool can machine different size of chamferNeed different tools to machine different size fillet
CoatingThere are still sharp edges at the chamfer, and the coating is easy to peel offIf the surface needs to be coated, fillet is the first choice

Therefore, in terms of economy, chamfering is better than rounding. When there are no special requirements, chamfering is preferred for outer surfaces and planes. The corners of the side walls of the inner cavity should be rounded as much as possible, because during the cutting process of the tool using the side edge, the corners will leave the radius arc of the tool. If the side walls of the inner cavity are processed into chamfered or right angles, auxiliary processing equipment such as EDM is required, which will result in relatively high costs.

The tool cost of chamfering will increase proportionally with the increase of the edge radius, and the rounding of the corners regardless of the occasion will cause unnecessary machining costs.

Here are 4 questions to think about before adding chamfer or fillet to your design:

  1. What is the role of chamfer or fillet?
  2. Are the chamfers and fillets necessary for the part?
  3. Is it cost-effective to increase this design at the number of planned production?
  4. How to check tolerances?

If it’s just proofing, the cost per part is already high, and adding chamfers or rounded corner designs is not cost-effective. But if mass-produced, the cost per part will not increase much and is cost-effective. Whereas for casting or forging processes, rounded corners are not only cost effective, they are a must.

The smaller the tolerance, the higher the machining cost. If determining that size is not important, you can remove the chamfer from the solid model and add a note to the drawing stating “Chamfer sharp edges and give range values for chamfers or arcs”.

Therefore, if you want to save costs, a necessary principle for designing chamfers and fillets is: to meet the requirements, add as few strict tolerances and large-size fillets and chamfers as possible.

How do you dimension a chamfer drawing?

There are two ways to dimension chamfers: one linear dimension and one angle; two linear dimensions.

With a linear dimension and an angular dimension, the linear dimension is the distance from the dimension surface on the part to the start of the chamfer.

linear dimension and angle dimension chamfer
linear dimension and angle dimension chamfer
Two linear dimensions Chamfer dimension style
Two linear dimensions Chamfer dimension style

45° chamfer dimension:

leader style
leader style

When the chamfer angle is 45°, it can be set according to the dimensions shown here, with a certain distance and angle. Note that this distance can be applied both vertically and horizontally, not diagonally. This method is only available for dimensioning with 45° chamfers.

45° chamfer dimension
45° chamfer dimension
Author: Mose Li

Author: Mose Li

Director of Project Engineering at 3Q Machining

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