My notes here

http://stonysmith.com/wired/scaling.asp will give you an indirect answer to this topic.

Here's a hyper technical answer:

For maximum accuracy, The size of a facet needs to be 1/2 of the resolution of the printer. Since the resolution of the printers is not published by Shapeways, we can instead us the rated "accuracy" number they

do publish..

For example, WhiteStrongFlexible has an accuracy of 0.15mm - that means you should design facets no larger than 0.075mm - if you do, your model will be more accurate than printer can produce.

The problem will be that at 7cm in diameter, that means that for maximum fidelity, you need ~3000 segments around the circle of the cone, and ~1500 segments along the length. That would give you a rectangular polygon count of 4.5m quads or 9.0m triangles. The trouble is that Shapeways only allows uploads of 1m triangles, so a highly accurate model could not be uploaded..

So somewhere on your model, you have to sacrifice a bit of fidelity.

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But again, that is the technical answer. You can like achieve something generally smooth and still stay under the 1m triangle limit.

Note: if you are printing in Ceramic, the model is dipped in glaze, so the faceting will be substantially reduced. Also, if you're printing in any of the "Polished" materials, then smaller facets will is also significantly smoothed out.