Difference Between A Chamfer and Fillet – When to Use Chamfer and Fillet


In CNC machining, in addition to sharp corners, corners can also be designed as chamfers or fillets. The difference between chamfer and fillet is a basic factor that designers must consider, which affects the difficulty and cost of part manufacturing. Then you can have a better understanding of when to use them.

Difference Between A Chamfer and Fillet - Chamfer vs Fillet

Generally, fillet and chamfer will lead to additional CNC machining costs and reduce production speed. Therefore, when to use fillet and chamfer requires further consideration.


What are Chamfer and Fillet?

Chamfer refers to inclined edges or corners of parts, and the chamfer can remove burrs for easy assembly. There are three types of fillet mechanisms: chamfer fillet, concave fillet, and convex fillet. 

Fillet describes rounded edges, or corners of parts to eliminate all sharp corners, which can improve the appearance and service life, and avoid sharp corners from hurting users. 


– Fillet can reduce the pressure on the part, distribute the stress on a larger surface, and help prevent sudden deformation of the compressed part. It is also the best choice to eliminate sharp edges. Smooth edges created by fillets are also easier to coat and paint. Conversely, chamfering will cause the coating to peel off over time.

– A chamfer is more prone to wear because of its sharp edges, but they are safer than sharp corners because these edges are covered. 

– Chamfer has a higher tolerance than a fillet for assembling mating pieces. 

– Chamfer holes enable smooth movement and insertion, making them ideal for allowing the male part to join the female part smoothly during assembly. More crucially, you can build a chamfer of varying diameters with a single tool.

When to Use Chamfer and Fillet

In product design, many factors need to be considered whether and when to use chamfer or fillet. From the function, position tolerance, cost, and other aspects of CNC machining parts.

1) Function

Considering the end use of your CNC machined parts, are sharp corners more likely to damage the environment? Will this part be used for load-bearing applications? If used, how much weight should CNC machined parts bear? Consider whether the product function depends on the existence of chamfers or fillets. For example, should parts be painted or coated, or should varnish be worn for a long time? Does the assembly have to match the mating parts exactly, or is there some margin? Answering these questions will help you decide which corner to use.

2) Location 

It is important to consider whether the corner you are designing is inside or outside the CNC machined part. Careful consideration of the outer edge is more important because it is almost always more pronounced, more susceptible to external conditions, and wears away over time. However, it is also important to consider internal chamfers or fillets when designing suitable holes for shafts. It is recommended to chamfer along the edge of the hole because chamfering the hole moves the pin and makes it easier to insert the fastener.

3) Tolerances

Optimizing dimensional tolerance is an important part of product design, especially when machining parts in CNC. Determine the accuracy your product needs to achieve and how incorrect measurement results affect the function and fit of the product. In addition, understand the importance of tolerances for ensuring the performance of CNC machined parts and consider how to check them. Note that applying very strict tolerances can be expensive, and chamfering usually increases tolerances.

4) Cost

Applying chamfers and fillets can be expensive. Consider whether fillets and chamfers are the keys to the success of CNC machining parts or just additional benefits. If you really need a special angle, please consider how many parts you need to manufacture, because this will also affect the cost of CNC parts.