Kanye might be right to worry -- the laws against 3D printing are pretty lax. But there are a few things that are illegal to 3D print.
3 Ways to Break the Law With 3D Printing
Here are three things that are illegal to print with a 3D printer:
Patented Objects: Having a patent on an invention or innovation means no one else can create, use, or sell a product without the patent holder's permission. Therefore, 3D printing of a patented object is illegal, and the patent holder could sue for patent infringement. Here's one drawback, however: in order to obtain a patent inventors must file a patent application with detailed plans of what is being patented. So just by seeking legal protection, you may be giving counterfeiters the means by which to copy your invention.
Assault Weapons: For the most part, 3D printing of guns is unregulated, and it is legal to manufacture firearms for personal use without a license. But there are limits. In jurisdictions where the possession of assault weapons is banned, that includes weapons printed at home. And printing undetectable guns is still illegal. It's also possible that disseminating 3D printing plans for guns may be illegal. The State Department ordered plans for 3D guns to be removed from online forums, although the case is under appeal.
Bombs: This one should be fairly obvious. No, you cannot 3D print a thermonuclear bomb.
Think of it this way: if it's already illegal to own, 3D printing your own version at home won't magically make it legal. If you still have questions, you may want to contact an experienced attorney before hitting "Print."
Violating someone's trademark with your 3D printer may invite civil action. But if you violate gun laws by printing a gun unlawfully, you may find yourself in the market for a criminal defense attorney.