You could ban making them but you cab't ban release of ideas and information like this

You can ban it.  You just have a real hard time trying to enforce the ban.

We have lots of software and engineering information that's prohibited or controlled when exporting to a foreign person, company or gov't agency.

Encryption software comes to mind as an example.

So, if 3D CAD plans are banned for certain projects (firearms parts), it would b enforced just like copyright and digital rights media laws:  when careless violators are identified.

I understand that intellectual property is protected at various levels and that of course some information is protected by the government but I think this goes beyond a specific program and is not a copyrighted material either.

The government cannot ban books like the anarchist handbook, they cannot arrest you for telling another person what chemicals to mix to form a bomb. Of course a chemical recipe is a bit simpler than the instructions to print a firearm.

Books are not printed by computers based off of a computer file, do you think the government can legally prevent someone from printing the book where they couldn't prevent it being written by hand? I know a specific material like classified information could be regulated but the idea of banning a whole type of information seems problematic.

Why are you talking about books?

This is about digital CAD files that permit 3D printing. 

We are not talking about national security classifications, but classes of materials and information.  For example, PGP encryption software was listed under the classification of munitions to control its export.

https://en.wikipedia.org/wiki/Export_of_cryptography_from_the_United_States

"Seems problematic" is purely your opinion.  The fact is, there are classes of information that are banned, regulated, restricted or otherwise controlled by law.

STL files
But lawmakers have little understanding if any about additive manufacturing.
I dont have any experience with CAD 2 years ago when I started 3d printing. The design process has a steep learning curve. I only use FreeCAD and though there are way better CAD programs like Solidworks and Fusion 360 it takes another effort to learn them.
Additive manufacturing parts have their weaknesses.
A person would still need to learn how to print the part. Heat, extrusion parameters, speed, support where needed, retraction paraneters are just some items you need to know. You can waste hours and spools of filament learning.

A CAD file is a series of instructions for a computerized machine, a recipe book (for example) is a series of instructions for people. And a CAD file is not a program but a set of instructions for the program to execute.

I am not saying there are no grounds for regulating information but it runs the something that could be a slippery slope. Where do you draw the line between speech and a computer program when both contain instructions or information? What about blueprints?

Do you think the government could legally ban the public from having a computer program with a password?

If I were going to make a plastic gun I would just start with blocks of plastic and build one with power tools and hand tools.

STL files
But lawmakers have little understanding if any about additive manufacturing.

that's really a better solution but how would you contain the pressure of the cartridge?

Did the HPD troll really write what you quoted?

I suppose so. It seems better than an additive 3d printer. Blocks pf plastic would be like billets versus thermally fused, layered material. SLA printing might produce a better end item. I never had any experience with those printers, just read about them.
Since we are on this subject, I'm looking at this Prusa mini https://www.prusa3d.com/original-prusa-mini/ it's a really good price at $350 and it seems on par or better than a Lulzbot Mini 2 at almost 4 times the price. I don't like the Mini's head. I had to get a silicone sock to prevent it from cooling while printing
ANyone have a Prusa? I have heard good things about them

https://www.kitv.com/story/41605609/hawaiis-attorney-general-announces-lawsuit-over-release-of-3dprinted-guns

it's not that simple as many believe...this isn't Star Trek and a 3d printer is not a replicator.

"tea hot" - CPT Picard

i'm shocked darmock hasn't corrected your quote yet

that's really a better solution but how would you contain the pressure of the cartridge?

A CAD file is a series of instructions for a computerized machine, a recipe book (for example) is a series of instructions for people. And a CAD file is not a program but a set of instructions for the program to execute.

Uh, as someone who has extensive experience with Computer Aided Design, that’s not how CAD works. As well as someone who is very familiar with CNC machining, Computer Aided Manufacturing (CAM) software (like Fusion 360) is what is needed. Or Computer Aided Engineering (CAE). The basis for that is the CAD file, as mentioned previously, but that is the template, not the sequence.

When being condescending, it usually helps to have the info correct.

Uh, as someone who has extensive experience with Computer Aided Design, that’s not how CAD works. As well as someone who is very familiar with CNC machining, Computer Aided Manufacturing (CAM) software (like Fusion 360) is what is needed. Or Computer Aided Engineering (CAE). The basis for that is the CAD file, as mentioned previously, but that is the template, not the sequence.

When being condescending, it usually helps to have the info correct.