Restrictions on 3d printer that would require printers to scan for "gun parts" are unconstitutional.
It is clearly evident from the available information that such a restriction cannot be implemented, but nonetheless, we should ignore that for a moment and bring ourselves to examine the constitutionality of such a proposal.
The 4th Amendment allegedly protects us against unreasonable searches and seizures without a warrant. If a model is searched for "gun parts", what is that other than a search? The fact that private party (the gun detecting software vendor and 3d printer manufacturer) is compelled to perform the search does not free the government of 4th amendment restraints.
Skinner v. Railway Labor Executives’ Ass’n, 489 U.S. 602 (1989) Federal regulations required or authorized private railroads to obtain blood, urine, and breath samples from employees. Fourth Amendment applied. A private railroad acting because of governmental compulsion was an “instrument or agent of the Government.”
And
City of Los Angeles v. Patel, 576 U.S. 409 (2015) Ordinance required private hotel operators to maintain guest records and immediately produce them for police inspection. Government cannot automatically avoid the Fourth Amendment by imposing recordkeeping/production duties on private businesses. The inspection regime was unconstitutional without adequate precompliance review.
The fact that a search of the 3d printer files offends the 4th amendment cannot be more clear than these two cases make clear.
Just because the government compels a private party to install the spyware, does not exempt the search from the 4th amendment because it is conducted by "vendor software".
Even if such a search could possibly be upheld under the administrative search rule (it cannot), it would fail because 3d Printers preventing the print violates an important rule around such administrative searches:
An administrative search will not be constitutional unless pre-compliance review by a neutral decision-maker is available. Los Angeles v. Patel, 576 U.S. 409 (2015)
It is therefore clear as daylight that such restrictions are unconstitutional, and any such search is a form of treason against the constitution.