You are correct, there is no way to define a nice curved shape if you are restricted to representing that shape on a 2D drawing. My company has never used 2D drawings to fully represent a 3D shape.

The F-16 control stick takes up something like 9 “J” sized sheets. A “J” sheet is three “D” sheets long. The drawing views get into the high double characters. That isn’t even a full description, it technically was controlled by the drawing, but I’m told that really there was a master pattern built; carved from mahogany.

So, can you define these curvy shapes? No, not really. What do we do? “NOTE 1: EXTERIOR GEOMETRY MUST CONFORM WITH THE CURRENT REVISION OF CAD FILE 123456-1″

Thus, we only work with suppliers that are able to take our CAD file directly and turn it into a model. Our current casting supplier, when we do small runs, actually uses a 3D printer to make the pattern for the investment castings. The CAD data can also be used directly in a CMM machine to compare the product with the reference. Most tooling shops for plastic injected molds should be able to make tooling from CAD data, they are using CNC software to create their toolpaths.

So, my company has been making curvy parts since the 1960s. It is now quite a bit easier with CAD, but it was always possible. It never involved (except by those crazy F-16 guys) using a 2D drawing as reference.