In the old days, when Xerox machines were first made, people realized it was easy to copy documents, artwork and other designs without having to first draw them. I don't think we need to gue$$ what was first copied when Color Copying machines came on the scene!
The issue then and now is copyrights to original works. Just because you can copy and print a copyrighted work perfectly does not mean that that act is NOT an infringement on the holder of the copyright. Copyrights are unique interpretations of an idea fixed in a medium. Ideas themselves cannot be copyrighted.
Also, this holds for 3D printing. Just because I can take an object, measure it exactly with my digital caliper and using those measurements design it and then print it....doesn't mean that I haven't infringed on a copyright.
Not all items are copyrighted or capable of being copyrighted that have been made to a scale. Scaling an existing full-sized object does not create a copyright in the reduced-sized object. This is true when the object scaled is already copyrighted. We know this from the trains we buy.
In order for Lionel or MTH to make an existing train, the must first obtain permission from the copyright holder to use any logo or other design on the engine. This applies to existing copyrighted objects. Copyrights last a long time, thanks to Disney and congress.
This is defiantly true for newer locomotives and other train cars and parts. Not so much for older steam engines or parts of them, except maybe logos and designs.
Further, let say I want to 3D print an existing trackside signal. So I take a picture, and use the picture to design and make a 3D print of that signal. Have I infringed on the signals owners' copyright? The first question is; "Does the signal owner actually have a copyright on the signal design?" remember that a copyright is a unique interpretation of an idea. The idea is a trackside signal that conforms to a railroad standard. So is the owner's interpretation unique or merely a simple copy of a pole with attached lights that conform to specific railroad standards as to height and other illumination standards?
This gets a bit more complex when we see that UP and NYC use different signal designs; is THAT a unique interpretation ?
Clearly, when Lionel designs and makes a unique part not based on an existing design idea, they own it.
So I can't make it. please don't ask.