Thin ‘solid’ parts ending up hollow.

I am trying to print some solid ‘U’ shaped brackets with 20mm (inside) sides to clip on to some 20mm box profile. The clip is currently 2.5mm thick. The first one printed fine but I slightly increased the lug diameter (not wall thickness). When printed again it came out as a shell and completely hollow. After trying many setting the one that has most effect on this is ‘layer height’. Either increasing by .01mm or decreasing can improve the problem but not eliminate it. I could understand if it had to leave out a single extrusion due space but it leaves out about 5. Sometimes it attempts to infill with dots but they don’t do anything to hold it together.
Bizarrely, if I adjust the layer height to get the best infill on a single bracket, then place 2 of them on the bed the infill goes wrong again and needs adjusting.
I understand a smaller layer height might produce a wider ‘squished’ filament but putting 2 identical objects on the bed shouldn’t mess that up?

edit, I should add that it is not a printer problem. I check and fix the gcode display before wasting ABS - well most of the time.

Edited 1 time(s). Last edit at 08/29/2013 11:30AM by Vince.

I've seen some changes in the way Slic3r handles either thin shapes or infill of small areas. I have seen changes between 0.9.3 to 0.9.8, and 0.9.10.

But, since you say the shape is not infilled when you enlarge it, I wonder if there's some interaction between the "solid infill threshold" and normal infill somehow.

I sometimes make the nozzle diameter slightly smaller in Slic3r, this makes it 'think' it has more room for another line and fills in better. As an example I almost always print with a .35mm nozzle and if it leaves hollow areas I change it to .30mm in Slicer. Won't hurt anything just makes it think there is a slight more room to lay a middle pass.

Same problem here. It's better with 0.9.8 but not solved. At the moment I try to compile the sourcecode to test the current "master" version.