Ceramic Machining: How to Choose Between Chamfers (C) and Fillets (R)

In ceramic machining, one of the most common questions we discuss with customers is:

“Can this corner be made as a sharp 90-degree angle?”

In most cases, the answer is no.

Unlike metals, ceramics cannot reliably maintain sharp corners. Instead, corners should be designed with chamfers (C) or fillets (R). Understanding why this is necessary—and how to choose between C and R—is critical for successful ceramic part design and manufacturing.

Why Sharp Corners Are Not Recommended in Ceramic Parts

Ceramic materials are characterized by high hardness and high brittleness. While these properties make ceramics excellent for wear resistance, thermal stability, and electrical insulation, they also introduce a key limitation:

Sharp corners create stress concentration.

At a 90-degree corner, mechanical stress, thermal stress, and residual machining stress tend to accumulate. In ceramics, this often leads to:

Edge chipping
Micro-crack initiation
Fracture during machining, assembly, or service

In addition, ceramic cutting tools cannot achieve the same sharpness as metal tools. Tool geometry, tool radius, and brittleness of the material all make true sharp corners impractical.

For these reasons, sharp internal or external corners should be avoided at the design stage.

Chamfer (C) vs Fillet (R): What’s the Difference?

Chamfer (C) is a straight, angled cut applied to a corner.

Commonly a 45° chamfer
Designated as C0.5, C1.0, etc.
Example:
- C0.5 means 0.5 mm is removed along both adjacent edges

Chamfers are simple, economical, and widely used—especially on external edges.

Fillet (R) (or radius) is a rounded corner formed by a circular arc.

Designated as R0.5, R1, R2, etc.
The value represents the radius of the arc
Example:
- R1 means a 1 mm radius fillet

Fillets are highly effective at reducing stress concentration and are essential in internal corners.

The Most Practical Design Rule

External corners are chamfered (C-corners), while internal corners are rounded (R-corners).

For external edges, chamfering is easier, more efficient, and less costly to machine.

However, for internal corners, rounded corners are essential, and C-corners are practically impossible to produce on internal corners (due to tool interference).

Conclusion

Choosing between C and R is not just a drawing detail—it directly affects whether a ceramic part can be machined reliably.

In summary:

Ceramics cannot handle sharp corners like metals
Chamfers (C) are ideal for external edges
Fillets (R) are essential for internal corners
Proper corner design improves strength, yield, and cost efficiency

If you are unsure which edge treatment method is suitable for your ceramic parts, we recommend consulting us in the early design stages. Jundro Ceramics is a manufacturer with many years of experience in advanced ceramic machining and can help you avoid costly modifications later.