Oh you used light-based AO? That is also a ray-traced effect and would experience the same kind of problem. I don't use light-based AO ever, because it is the most buggy ray-traced effect there is in Poser. No adjustment will ever make it work right.

I generally use material AO nodes.

So that's a good clue - you have AO problems.

I'm pretty sure this is all due to trying to use ray-traced effects with displacement. We can work around these, but we have to respect Poser's limitations. Remember the third workaround is more polygons. You may want to try it.

BTW: Here's you locomotive after a 12 hour run. Needs washing again :)

I'm off to bed now. I'll check on you tomorrow.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)