Guides / Design

What Is Possible and What Is Painful: Features in a Ceramic Part

June 29, 2026

Features that take minutes in aluminium take hours in sintered ceramic, and some of them do not take at all. Knowing which is which before you finish the drawing saves a revision cycle.

Holes

Round holes are made by diamond core drilling on a rigid machine with flood coolant, by ultrasonic machining, or by grinding with a small wheel for larger diameters.

Practical guidance:

Question	Comfortable	Possible	Expensive or specialist
Diameter	1 mm and above	0.5 mm	Below 0.3 mm
Depth to diameter	Up to 5 to 1	Up to 10 to 1	Beyond 10 to 1
Position tolerance	±0.05 mm	±0.02 mm	Tighter, needs ground datums
Blind hole flat bottom	Slight cone accepted	Flat with extra work	Flat and sharp cornered

Always chamfer both ends. Breakout chipping on hole exit is one of the most common scrap causes in this niche. Where the back face cannot be chamfered, tell the shop, so they can back the part with a sacrificial support.

Keep holes away from edges and each other. A ligament thinner than about one hole diameter is a crack waiting to happen, in grinding or in service.

Cross holes are the hardest case. The second hole breaks out inside the first, unsupported. If you need them, expect an internal chamfer and a slightly higher scrap allowance, or move the intersection so it happens in thicker material.

Slots and pockets

Slots are ground with a wheel, so they inherit the wheel geometry.

• The slot end radius equals the wheel radius. Draw it that way
• A slot narrower than about 1 mm needs a thin wheel, which is fragile and slow
• Deep narrow slots suffer wheel deflection, which shows up as taper
• Pocket floors are rarely perfectly flat and sharp cornered, so give the floor to corner junction a radius

If the slot exists to clear a metal part, consider making the clearance in the metal instead.

Threads

Ceramic threads exist. They are ground, ultrasonically machined or occasionally formed green before firing. All three are slow, and a ceramic thread is also mechanically fragile: the thread root is a stress concentration in a material with no yield.

Better answers, in rough order of preference:

1. Clearance hole and a metal bolt with a washer that spreads load
2. Clamped joint with a flange or a collar, avoiding point loads
3. Brazed or metallised metal insert, so the thread lives in metal. See metallising and brazing ceramic to metal
4. Shrink fitted metal sleeve, if the expansion mismatch is managed
5. Ground thread, when nothing else fits and the budget allows

If you do specify a thread, use a coarse pitch, keep it short, put a generous lead chamfer on it and never let it bottom out.

Green machining changes the answer

If the part is going down the green machining route, holes, slots, pockets and even threads are cut cheaply in the soft state before firing, then everything shrinks. Features that are painful to grind become ordinary, and the constraint moves to tolerance instead. This is the single biggest reason to decide the route early. See green machining or hard grinding.

A common and effective hybrid: green machine the features, fire the part, then grind only the two or three surfaces that carry tolerance.

Before you send the drawing

• Chamfer every hole at both ends
• Replace sharp slot ends with the wheel radius
• Ask whether any thread can become a clearance hole
• Mark which holes are functional and which are clearance
• Say if the part will be green machined, so the shop quotes the right route

More drawing level guidance in 12 design rules for a ceramic part.

Send your drawing and we match it with up to 3 shops that will tell you which features to move before they quote. Reply within 24 business hours.

Frequently asked questions

Keep reading

• Joining Ceramic to Metal Without Cracking It on the First Cycle
• What Tolerance and Finish You Can Actually Ask For on a Ceramic Part