ok, i think i get the problem, the cube of 20x20x20 has different boundaries then the 20x20x20 cilinder, while you would expect the edges to meet, since.. they're the same width.. thats strange indeed.
If you size 2 primitives the same size, you'd expect them to have the same size, i totally agree.

However.. the default bryce cube isnt 20x20x20, it is actually 20.48 x 20.48 x 20.48... might not look significant to add the decimals but it is :) maybe thats the prob?

try makin the cube it 20.48x20.48x20.48.. does that solve it?

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