That's not a coincident surface -- that's the top and bottom of cyl's with
different radii.  I agree that would be a problem if the top edge were in
the frame, but we're looking at the inside curve of the smaller one.

I tried it anyway, and it makes no difference.

--John

"Chris Huff" <chr### [at] maccom> wrote in message
news:chrishuff-C04E3E.20015214032001@news.povray.org...
> In article <3ab00fe5@news.povray.org>, "John M. Dlugosz"
> <joh### [at] dlugoszcom> wrote:
>
> > difference {
> >    intersection {
> >       cylinder { <0,0,0>, <0,18,0>, 12 }
> ...
> >    cylinder { <0,0,0>, <0,18,0>, 11.5 }
>
> You have a coincident surfaces problem here...try using < 0, 18.001, 0>
> in the second cylinder.
>
> --
> Christopher James Huff
> Personal: chr### [at] maccom, http://homepage.mac.com/chrishuff/
> TAG: chr### [at] tagpovrayorg, http://tag.povray.org/
>
> <><

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