[quells]

It’s incredibly difficult to form conventional ceramics into “the correct shape to begin with” with even millimeter tolerances because it shrinks twice during production. First when the liquid from the slurry/clay evaporates, and again when the particles sinter together during firing in the kiln. Both of these are non-linear and can cause warping with complex geometries.

EDIT: binders also typically burn off during firing, which further complicates changing shape during firing.

[hinkley]

It’s kind of amazing that you can get a ceramic container where the lid fits snuggly. Some of that comes from modifying the greenware (dried but unfired clay) but I think most of it is exacting tolerances for inputs and processing. Clay from this one quarry. This much water. These building temperatures and humidity. This exact furnace temperature and time.

[ruste]

The only way I've seen this done is by lapping the touching surfaces after firing.

[amluto]

One can fire a pot with the lid on it in the kiln. They tend to deform together. Of course, this requires that the mating surfaces not fuse together and may also produce a non-rotationally-symmetric interface.

[hinkley]

I feel like I've watched videos where people make Japanese and/or Korean ceramic cook pots and I can't for the life of me remember how they kept them from warping, just that they do.

The only trick I do remember is don't glaze the contact point between the two pieces. That not only adds thickness variability, but if glaze touches the bottom of the kiln you fuse to the bricks, so you have to elevate anything glazed, and elevating increases warping.

[creeble]

How do they create things like ceramic turbo turbines and ceramic exhaust manifolds? Seems like the shrinkage problem would prevent these close tolerances.

[adrian_b]

The same shrinkage problem exists for the ceramic tooth crowns.

The vendor of the dental ceramic provides a program that uses a mathematical model of the shrinkage to compute the form required for the ceramic crown before sintering.

Of course the mathematical model is not perfect so the dentist may still have to do some small adjustments to the sintered crown.

[lazide]

Lots of trial and error and tossed parts during manufacture. Neither of those parts are known for being cheap.