I'm working on a project to build a model M1 Abrams, and will likely extend to doing numerous other tanks at points somewhere past actually getting a business started. big problem is most tanks have curved surfaces that don't have fixed radii. I'm looking at the glacis plate(front armor on the hull) on the Abrams, and things like the turret on the M4 Sherman and a few other places. This has similarities to making fenders and car parts where spline type curves are used. While some parts of the curves don't necessarily need to be well defined, I do need decent models that can have some dimensions fixed(for defining attachment points and scale stuff etc.). My Google-fu is failing me on getting a decent modern tutorial for this, most are like 10 years old, or not related. I'm also restricted in what material I can use to get data, since this is a commercial project, and can't always guarantee Ed Gruberman's model on Thingiverse is quite right, assuming Alibre can open it and let me turn it into a vacuformed part and accessories.