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Ceramic Part Design Guide
The limits a ceramic shop works inside, in one page. Keep it open while you draw, and your first quote will come back with a price instead of a list of questions.
Geometry limits
Comfortable means most shops quote it without comment. Possible means it costs more and needs the right shop. Beyond that, expect a redesign conversation.
| Feature | Comfortable | Possible | Why the limit exists |
|---|---|---|---|
| Wall thickness | 1.5 mm and above | 0.8 to 1 mm | Thin walls flex and chatter under the wheel, then chip |
| Internal corner radius | R0.5 mm and above | R0.15 mm, shallow only | The wheel radius sets the corner radius |
| External edge | Chamfer 0.2 x 45 deg | Sharp, with a scrap allowance | An unchamfered edge is a crack origin |
| Hole diameter | 1 mm and above | 0.3 to 0.5 mm | Core drill rigidity and coolant access |
| Hole depth to diameter | Up to 5 to 1 | Up to 10 to 1 | Swarf clearance and tool deflection |
| Slot width | 1.5 mm and above | 0.8 mm | Thin wheels deflect, which shows up as taper |
| Aspect ratio of a slender feature | Up to 8 to 1 | Up to 12 to 1 | Fixturing and handling breakage |
| Threads | Avoid, use clearance holes | Coarse, short, ground | Thread roots concentrate stress in a brittle material |
| Hole to edge distance | One hole diameter | Half a diameter | A thin ligament cracks in grinding or in service |
| Flat bottom blind hole | Slight cone accepted | Flat, extra operation | Core drills leave a centre feature |
Going down the green machining route changes most of these, because the material is cut soft before firing. Decide the route first: green machining or hard grinding.
Tolerance and finish
Ground surfaces hold numbers that would be respectable on hardened steel. Surfaces nobody grinds are ten to a hundred times looser. Mark which is which.
| Requirement | As fired | As ground | Lapped or polished |
|---|---|---|---|
| Linear dimension | About 1% of the dimension | ±0.005 to ±0.013 mm | ±0.002 mm |
| Flatness | 0.1 mm and up | 0.01 to 0.02 mm | 0.005 mm and below |
| Parallelism | Not controlled | 0.005 to 0.02 mm | Below 0.005 mm |
| Roundness | Not controlled | 0.005 mm | Below 0.002 mm |
| Surface finish Ra | 0.8 µm and up | 0.2 to 0.4 µm | 0.05 to 0.1 µm |
The single biggest saving available. Count the features on your drawing that carry a tolerance tighter than ±0.05 mm. Every one of them is a ground surface with setup, passes and inspection behind it. On most drawings, two or three of them are doing real work and the rest were inherited from a template.
Drawing notes that remove the questions
Copy these, edit the numbers. A drawing carrying this block quotes faster and cheaper than one that does not, because nothing has to be guessed.
Deeper reading: 12 design rules, corners and chipping, tolerance and finish.
General notes block
- Material: [grade, purity, minimum density, maximum grain size].
- Features marked G are ground after sintering. All other dimensions as fired, ±1%.
- All external edges chamfered 0.2 x 45 degrees unless noted.
- Hole edges chamfered both ends 0.2 x 45 degrees.
- Internal corners R0.5 minimum, larger acceptable.
- Face A lapped flat within 0.005 mm, Ra 0.1 µm max. All other surfaces as ground.
- Maximum acceptable edge chip: [length x depth]. Chips within this limit are accepted.
- Function: [one sentence on what the part does and which surfaces matter].
Ten second check before you send it
Is every tolerance doing a job?
If a feature does not fit, seal, slide or mount, it does not need a number tighter than as fired.
Does every edge have a defined chamfer?
"Break all edges" is a metal instruction. Give the shop a dimension.
Is every internal corner drawn with a radius?
If the corner exists for clearance, undercut the ceramic or chamfer the mating metal part instead.
Are the datums on surfaces that will be ground?
Measuring from an as-fired face passes that face variation into everything else.
Have you said what the part does?
One sentence changes the quote more than any other single thing on the drawing.
Questions designers ask
What is the minimum wall thickness for a ceramic part?
Around 1 mm is a comfortable floor for alumina on a part of ordinary size, and less is possible in zirconia because it is tougher. Below that the scrap rate and the price both climb, and the part needs supporting fixtures during grinding.
What internal corner radius should I draw?
R0.5 mm or larger wherever function allows. A grinding wheel has a radius, so an internal corner has one too. Small wheels can reach around R0.15 mm in shallow features, but they are slow, fragile and expensive.
Which tolerance should I put on a ceramic drawing?
Plus or minus 0.013 mm on ground features is a comfortable production tolerance, and plus or minus 0.005 mm is achievable with care. Anything not ground should be tolerated at about 1 percent of the dimension, because sintering shrinkage is proportional.
Can I reuse a metal drawing for a ceramic part?
Not without editing it. The general tolerance block, the sharp internal corners and the deburr note all need to change, and threads usually need to become clearance holes.
Drawing ready? Send it through.
We read the geometry, decide the route and match you with up to 3 shops set up for it. Free for buyers, reply within 24 business hours.