How mechanical surface modeling works

Some of you may wonder how you make models like this, especially the multi-curvature models are somewhat complex to make and requires the use of what CAD Designers call surface modeling, rather than straight blocks and cuts as most models are made.

I'll show how I made the lower ribbed side plate. This isn't a tutorial, just a short explanation of the process. If you want to learn there are free youtube video courses for most common 3D CAD systems on the market today., as well as plenty of companies teaching this professionally.

Making the ribbed side plate model I started from the helmet surface geometry.
I made an angled plane (as close to perpendicular as possible in this case) and make a cutting surface sketch.

I offset the surfaces to zero distance, making a copy of it to modify.

I extruded cutting surfaces from the sketch

I cut the outer profile, I then added Thickness to the cut surface (not shown).

Then I added the rib in the same way, cutting with an extruded sketch and in this case also cutting the sketch surfaces with the resulting cut surface and the previous surface.

The basic shape is formed but these are just surfaces (i.e. walls with no thickness) , not a solid possible to model with cuts for holes and the shell hollowing out I'm doing forther down. So I used the surface modeling command Knit to fuse the surfaces together and make a solid. 

Then I added radii.

Then I cut holes. 

I'm cutting with one plane here and a sketch is making the holes top direction and not perpendicular, I'll probaly change that later as it makes for a little crooked holes.

I marked the bottom for the Shell command. I choose to make the model 1 mm thick from the bottom with this.

Done. :)

Of course I skipped over some stages here but hopefully it explains some of the basics of surface modeling in 3D CAD systems and making it a solid you can more easily modify and cut to make holes.