This helmet is a copy of my but smooth. http://www.thingiverse.com/thing:325431
Here you can see perfectly, "how it is made"http://i1159.photobucket.com/albums/p627/Christopher_Z/ab_zpspzdxplhl.jpg
And here is improved copy of the same Chelm only cut and hollow inside and more correctionhttp://www.thingiverse.com/thing:391664
Both helmets is a copy of SketchUp https://3dwarehouse.sketchup.com/model.html?id=57ffd28975abba38480514d7f2edc0a3
My version is also a copy of the same Chelm but I do not write with is my only version 1 of the revised angle for adhesion.