Ugly top cover area for objects

Another print, another question... (sorry for that).
When printing round objects, the upper cover areay is almost always incomplete. I am not talking about the top layer here (that was another question that I posted). For example, for the famous "Cuddling Owls" object, the head portion looks weird. The top of the big owl is not "watertight". Could this be an issue with inadequate cooling? We have mounted a 40mm fan but maybe it is not aligned properly.
Here is the print (sorry for the blurry image).
[flickr.com]

Fan:
[flickr.com]

Or maybe it is an issue with the slicing settings. I used Slic3r and have chosen 2 perimeters and concentric top fill pattern.


Thanks,
Stefan

Edited 1 time(s). Last edit at 07/05/2013 08:09PM by Nicolinux.

Do you have your slicer set to slow down on small layers?

This looks like a common issue when there are tiny layers at the top of an object and the g code slows the print head down. The plastic needs time without having the head nearby to cool and harden. When the head slows down too much and stays in the same area too long, as it looks like it's doing here, then the top of the object can be misshapen.

Solutions: slow down less, cool faster, combine your object with other objects on the same plate (or print multiple copies of the same item) so that the head has somewhere else to go for a while

Thanks for the answer. I am using Slic3r and I guess I need to tell it to do so. The thing is, there is no specific setting for this case (as far as I can see). I can tell it to not slow down too much, but this would apply for all layers and not only the "caps" or "covers".

I loaded the generated gcode into Blender to have a better idea of the generated path. It looks like it is not a printer issue but as slicer problem. The generated path itself looks like it won't be watertight at the top. I guess I'll have to play with Slic3r a bit.

[flickr.com]
[flickr.com]

By the way. Is there a useful gcode viewer that can display gcode in 3D and where one can trace paths to see how the stack up?