Does anybody know how to setup material or render setting to avoid these black parts in render?
It is visible only from some view angle.
Any tips? Thank you for help.
download blend file
To move whole scene? If it helps it would be big surprise, hm . . .
(model is done in blender)
Hi vklidu, i think greyoxide mean it is a scaling problem.
moved the whole scene down by a factor of 1
Nice work, mib.
cannot see the black parts you mean here!
can you point or encricle the area with problem
i can see some shadows but that seems normal to me
have you try to add edgesplit to see if it goes away ?
also did you try to render with much higher samples like 500 ?
salutations
To me it looks to be a lighting issue. You are hiding the object itself but the shadows remain.
It looked like one of those models that people make in a specially branded program like LEGO. Excellent job on your model I’m impressed.
For the shading issue; in my case I didnt feel like there was any reason for it in that other model. There were no other faces in that location. When I moved it to an empty layer just to check it still had the issue. To me it felt like a bug that will probably be eliminated as cycles matures.
The cool thing about cycles is that you can turn on the rendered viewport and move the thing around to see if it still does it.
To preface I know pretty much nothing about this subject so this post may not be worth anything.
On further testing it seems like it may be related to the backfacing geometry node. It looks like it works fine when you are looking through a front then back face at an object. Whereas if you do this twice (through front face then back face then front face and back face again) it seems to introduce artifacts
Here it works no problem
And here it does not work
Again I really dont know much, but could this be a bug in cycles?
Try to increase in Integrator panel Max bounce and Transparent max Bounce to something > 25, maybe it is bounce limit.
Thanks for your attention to my question 
These shadows comes visible when faces are very close to each other. Also angle of view is factor.
@storm_st: THANKS MAN you are right !!! Integrator > Transparent > Max: 50 = clear render !!!
p.s.: more tests with coss section by material for cycles
So, OK I have one more - on previous (and this render) you can see some lights (reflections) on the floor that lights from invisible half of the model.
From previous render I thought it’s problem of metalic material, but it lights also with this pink diffuse shader too.
Even I use only transparent for whole model.
Any idea? Thank you again.
I tried to use a more elaborate Emission node.
Using a wave texture with bands I created a streaky emission.
Unfortunately then it gets obvious that the backfacing is from the individual faces of the model.
Which looks pretty odd.
Is there any way to get a PLANE at the place of the section which can be textured (not neccessarily an emission node, but maybe any shader node)?
Currently this method is pretty good for a single color section.
(sorry for hijacking the thread 
)
There could be ways with experimental builds from Graphicall.org
- Volume Shader - sound like the best solution
- or I saw last exp. build with some “Rendered Layer” option so maybe you can try “old” compositing technique
I posted here http://blenderartists.org/forum/showthread.php?168570 (it’s for 2.4x version, but for cycles in 2.6 it’s the same compositing I think)
I have managed to use the emission node only if it is a camera ray. That way it turns invisible for everybody else.
Should work in your case too, I hope.
Also I have used a UV Mapped image to have better control which parts should show the sectioning.
The attached blend file has a tube that is bend/twisted and has some deeper cuts that other parts.
Hope it might help somebody.
Attachments
SectionTest.blend (136 KB)
Volume particles have absolutely different shader, compared to surface color, and reflected particle color controlled by Phase function, I have only 1 node Volume BSDF for that, you can try change Color to something other then 1.0. Particle have no UV coordinate space, only 3D space, you need to make 3D coordinate from Position, Object, etc. I think there will be very nice coordinate space (U,V, normal) for easy volume fur like effects, but do not know how to make it in general, for sphere or tube it easy, using a couple of math nodes. You need patched Blender for that, of course. And 10X-100X render time to clear noise. And Volume patch have not yet emission node for particles.
a bit late, sorry -thnaks for answer 
do you have some nodes set up for using volume as examples?
i would like to begin experimenting with thsi volume feature in cycles
but not certain how it works!
thanks
more about cross section
few volume test with blends
thanks i will experiment with this new volume feature
by the way have you seen any API commands to make script using cycles nodes ?
or it has not been done yet may be!
i just tested the filter file
with an SVN having the volume node
and the middle of the filter is empty
but the nodes for volume is not shown being connect to ouput
so i guess the node set up is not complete
can you show final node set up for this so it works like shown in thread !
thanks
salutations
did you correct the node setup and the file sample
right now seems that most files are not available !
and is i possible that volume does not work on vista 32 bits ?
did a simple tst and does not seems to do much
but i may not have the right set up !
mind you i do have a special SVN for volume on vista
but have not been able yet to make one volume texture !
thanks