1st is religion, assembly, press and speech
Do you mean 1st amendment is infringed because you expect this to be taken down because it's a 3d printed gun?
It's not illegal to deign share or make 3d printed guns. but the same freedom of speech allows forums to limit what gets shared there. so It's reasonable to assume 3D printed gun files might get deleted from some sites if it violates their terms which literally IS them exercising 1st amendment rights, regardless of legality in general
A related discussion might be the sharing of bomb-making techniques
Or do you mean 2nd amendment bearing arms infringement? I think the argument that banning 3D printed guns or sharing the files could be unconstitutional. But kids with a hobby printer and a grudge are not the well-organized militia carrying muskets against British tyrants that the amendment initially sought to protect. So I can see that being an interesting debate, whichever amendment you intended o call out