Guides / Process

Green Machining or Hard Grinding? The Choice That Sets Your Ceramic Price

September 18, 2026

Two shops can quote the same ceramic drawing and come back with prices that differ by a factor of three. Usually neither of them is wrong. They picked different routes.

Route A: green machining, then fire

The blank arrives as a soft pressed body, roughly the consistency of hard chalk. It is turned, milled or drilled with ordinary carbide tooling at high feed rates, then fired.

What you get:

• Fast cutting and cheap tooling
• Complex shapes, undercuts and features that would be slow to grind
• A low piece price once the geometry is proven

What you pay for it:

• Shrinkage of 15 to 25 percent on every dimension. The shop cuts the part oversized by a factor measured from its own kiln and its own powder lot
• As-fired accuracy near 1 percent of the dimension, so a 60 mm diameter lands within about 0.6 mm
• Distortion. Long thin parts and asymmetric sections do not shrink evenly, and flatness suffers
• A firing slot, which is scheduled in batches and adds weeks

Green machining suits volume, simple geometry and parts with no tight fit: standoffs, tubes, covers, furnace fixtures.

Route B: hard machining, ground after firing

The blank is fired first, then ground with diamond wheels. This is the route most buyers picture when they think of precision ceramic work.

What you get:

• ±0.005 to ±0.013 mm on ground features
• Flatness under 0.005 mm on a lapped face, and finishes down to Ra 0.1 µm
• No shrinkage guesswork. What is ground is what you measure
• No pressing tooling, so single pieces are practical

What you pay for it:

• Grinding hours. Removal rates are a fraction of metalworking, so stock removal is the bill
• Wheel wear and dressing, which is real money in silicon carbide and silicon nitride
• Chip risk at edges, cross holes and thin walls, which shows up as scrap

Hard machining suits prototypes, fits, seal faces, anything inspected on a CMM and anything where a rejected part costs more than the grinding.

The hybrid, which is what production usually looks like

Green machine the bulk of the shape, fire it, then grind only the features that carry a tolerance. A typical insulator ring is green machined to shape, fired, then ground on the bore and one face. Everything else stays as fired.

This is why the single most valuable thing on a ceramic drawing is a clear split between critical and non-critical features. Without it a shop either grinds everything, which prices you out, or grinds nothing and ships a part that does not fit.

How to mark the drawing

• Put real tolerances only on features that need them. Mark the rest as fired, or give them a general tolerance of 1 percent
• Call out flatness, parallelism and finish by face, not as a blanket note
• Define edge chamfers with a dimension. “Break all edges” is not a ceramic instruction
• Add a radius in internal corners. A sharp internal corner in a brittle material is a crack starter and a grinding wheel cannot reach it anyway
• State whether a face is a sealing, sliding or bonding surface. That single sentence often changes the route

What it means for your RFQ

If your part has one or two critical features and the rest is structure, say so and expect a hybrid quote. If everything is critical, you are in hard machining territory and the price will reflect it. If nothing is critical, green machining should be on the table and any shop quoting you a fully ground part is overselling.

For the wider picture, see the buyer guide to machined ceramic parts and what drives the cost.

Have a drawing? Send it through and we match you with shops that run the route your part needs. Reply within 24 business hours.

Frequently asked questions

Keep reading

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