Slic3r fail? After hours of printing this isn’t what I wanted. Despite 100% infill being set the walls between CF cards are printed as two thin shells. Shells that distorted at the bottom. Time to see if Simplify3D will do a better job.
I get that with slic3r quite often too.
There are couple of workarounds for that. Use smaller nozzle or decrese the extruion width for infill (and perimeters probably).
I just loaded it into Simplify3D and looked at the tool paths preview, it’s showing that it’s going to print infill after doing the outlines. Disappointing as I prefer the Slic3r GUI and Simplify3D keeps crashing on me with GPU driver problems.
Talk about a difference… Slic3r gcode: 2MB. Simplify3D: 20MB.
You can change extrusion width on slic3r to a smaller value to ensure infill is actually done on narrow places like the one you show. Experimental version will provide you 2D and 3D preview too, check before printing.
Experimental 1.2.6 crashes on my system shortly after loading any STL. Watching the status lower left around the infill generation.
You can try my suggestion with older versions too.
I’ve been checking on the print from Simplify3D, run via Octoprint. It’s looking much better. I’ll try your all your suggestions on the next thing I print, thanks for all your input.
So another question is what exported the STL file? Is it possible the geometry is such that the slicer can’t tell if those intermediate pieces are solid or not?
Mark made his model in FreeCAD which produces truely solid CAD models (not like SketchUp or mesh modelers). There should be no such problem.
FreeCAD exported it. And Simplify3D knew it was solid as it decided it needed fill in between. Sods law I had the settings to not put down a skirt and it started lifting so was aborted early. I’ll try again soon, it needs a calibration check, my z-probe is playing up again 
How thick, exactly, is that wall?
If your doing 100% infill always do one shell. If your wall is not a multiple of 0.8mm then when the shells can’t get in there every slicer I’ve seen just gives up. However if you do a single wall then the infill can get in there with every soccer I’ve seen. Why no slicer I’ve ever seen or heard of just applies the fill algorithm to the area it can’t do a shell I don’t know, but they don’t.
It’s 0.8mm. And I have a 0.4 nozzle. Somehow Slic3r is getting the speed/extrusion rate such that it lays two thin shell walls of 0.11 each, it’s logic possibly saying 0.8/0.4=2 = both walls done, no space left. Yet Simplify3D is also doing a pair of shell walls that it then fills. I’ll have to document all the details to see if anything stands out as wrong in my Slic3r setup and create some much smaller test objects to print.
Slic3r will let you set fill overlap. It’s good for bodging that sort of problem 
What are you making?
CF card holder to slide into my ThinkTank bag. I have a lot of them for my Google Maps Business Views work and other photography.