Support Problem - No shell on the supported surface - Jet Engine

[BastienExp 0]

Hello

 

I print this famous open source jet engine from thingiverse with Ultimaker 3 Extended and Cura (https://www.thingiverse.com/thing:1327093 ). I got problem with the print of the casing. There are numerous flanges on the casing parts (90° plane surfaces) and I'm very disappointed by the surface quality of these supported surfaces (roof interface with the support) in comparison with the supporting surfaces (floor interface with the support). I print with PLA for both product and support.  I tried two times without significant improvement. For the second print, I reduced "support Z distance", I added "Support horizontal expansion" and  "support Interface/roof". Even with this "support Interface/roof" the result is not really different. Below you will find the details of my setting and few pictures of the floor and the roof interfaces. For floor and roof interface, you can recognize zig-zag marks from the support. But for the roof interface, it looks like there is no shell on the interface, just the 50% infill.

 

First print:

-        Layer Height : 15 mm

-        Infill Density : 50%

-        Support Density 15%(zig-zag)

-        Support Z distance   0.15mm

 

Second print:

-        Layer Height : 15 mm

-        Infill Density : 50%

-        Support Density 15% (zig-zag)

-        Support Z distance  0.1mm

-        Support Horizontal expansion : 1mm

-         Enable support Interface/Roof : support roof thickness 1mm, Support Roof density : 30%

 

 

Would you have suggestions to improve my print  ? 

Is it possible to set a slower print speed or an higher infill density just for the critical area of my product  (the roof interface) ?

 

Thank you for the help