Honestly why 3d print any tools that are expected to handle significant force, its much more practical to make a hammer out of a sturdy bit of wood and shape a bit of steel to go on the end than it is to print one and expect it not to break the first time you use it. What if the nail is still sticking out and needs to be knocked in again a second or third time? Especially in a country where every hardware store sells hammers and there are hammer club catch ups where you can also get them from other hammer enthusiasts.
The whole 3D printed hammer thing is sensational journalism hyped up over a theoretical issue that really isnt an actual issue.