Guides / Design
The Most Expensive Line on Your Ceramic Drawing Is a Sharp Corner
June 15, 2026
Ceramic does not yield. A metal part with a sharp corner develops a small plastic zone that blunts the stress concentration. A ceramic part with a sharp corner keeps the concentration and waits for something to load it.
That is why corner and edge treatment is the highest leverage detail on a ceramic drawing, and the one most often copied over from a metal design without thinking.
Internal corners have a radius whether you draw one or not
Material is removed by a grinding wheel with a finite radius. You cannot grind a corner sharper than the tool that made it, and small wheels run out of stiffness and coolant flow quickly.
What that means in practice:
- A shallow feature can reach a small radius, in the region of 0.15 to 0.3 mm
- A deep pocket or slot needs a larger wheel and therefore a larger radius, often 0.5 to 1 mm
- Asking for a sharp corner forces the shop to either quote a slower process, quote an ultrasonic or EDM route, or come back with a question
If the corner exists for clearance rather than for function, there is a better answer: undercut the ceramic or chamfer the mating metal part. Clearance is cheap in metal and expensive in ceramic.
External edges need a defined chamfer
An unchamfered ceramic edge chips. It chips during grinding, during deburring, during inspection, during packing, during assembly and during service. Every chip is a potential crack origin, and a crack origin in a brittle material is a failure waiting for a load.
Write the chamfer as a dimension. Something like 0.2 x 45 degrees, or an edge radius of 0.2 mm, is enough to change the outcome. For parts that are handled a lot, or that sit in a fixture, 0.3 to 0.5 mm is better.
Do not write “break all edges” or “deburr”. Those are metal instructions. They tell a ceramic shop nothing about how much material to take, and the answer they choose will either be too little to protect the part or too much for your fit.
Where chipping actually starts
| Location | Why it chips | What to change |
|---|---|---|
| Hole exit | The tool breaks through unsupported material | Chamfer both ends, support the back face |
| Slot ends | Wheel entry and exit shock | Radius the slot ends, add run out room |
| Thin wall top edge | No material behind the edge | Increase wall, or chamfer generously |
| Knife edges from two tapers meeting | Zero material at the tip | Add a flat or a radius at the tip |
| Cross hole intersections | Unsupported break through inside a bore | Move the intersection, or accept a chamfer on the inside |
Subsurface damage: the part of the chip you cannot see
Grinding leaves microcracks below the surface. On a well controlled process the damaged layer is shallow, and finishing passes with finer grit remove most of it. On an aggressive process it is deeper than the finish suggests, and the part is weaker than its measurements imply.
This is why strength on a ceramic part depends on how it was finished, not only on the material. A lapped or polished surface is stronger than a coarsely ground one in the same material. If your part is highly stressed, specify the finish on the stressed surfaces and expect it to cost something. See lapping, polishing and flatness and how diamond grinding works.
Practical drawing language
- “All external edges chamfered 0.2 x 45 degrees unless noted”
- “Internal corners R0.5 minimum, larger acceptable”
- “Hole edges chamfered both ends 0.2 x 45 degrees”
- “Face A lapped, Ra 0.2 µm maximum, remaining faces as ground”
Four notes like these remove most of the questions a ceramic shop would otherwise send back, and they usually reduce the price rather than increase it. The rest of the checklist is in 12 design rules for a ceramic part.
Send your drawing and we match it with up to 3 shops that will flag the edges before they quote. Reply within 24 business hours.
Frequently asked questions
What is the smallest internal corner radius possible in ceramic?
It depends on wheel access. A small wheel can reach around 0.15 mm in a shallow feature, but 0.5 mm and above is far cheaper and more reliable. Deep features need a larger wheel and therefore a larger radius.
Why does my ceramic part chip at the edges during assembly?
An unchamfered ceramic edge is effectively a crack waiting to open. Clamping, handling and thermal stress all concentrate there. A defined chamfer or edge radius removes the sharp geometry and the stress riser with it.
Does a chamfer weaken the part?
The opposite in practice. It removes the most damaged, most highly stressed geometry on the part. The material lost is negligible compared with the strength recovered.
Need a quote for this part?
Send the drawing. We match you with up to 3 shops that grind this grade and reply within 24 business hours.
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