My (very uninformed) guess is that you could probably build a self-sustaining community using 3D printing, on the Alps or the Appalachian. (After all, our ancestors managed with stone tools.) Doing that on the South Pole will be challenging. Mars, forget it.

If you are persistent enough you could probably 3D print everything, I guess. Maybe you could 3D-print concrete and ceramic blocks to build a furnace that will be used to produce steel which will be shaped into a pipe (by another 3D printed machine) to transport hot gas to melt silicon oxide and produce glass.

However, after a few iterations, I guess people will ask "Why don't we just pour concrete over here in conventional way? That's much easier and cheaper."

I do think, however, that robotics and additive manufacturing will be critical to building significant parts of the machinery and buildings on Mars.

Certainly, sometimes you will use traditional manufacturing methods to construct things. But additive manufacturing has different capabilities and it will be used for different things. And unlike some people who claim additive manufacturing can't be used for anything, I believe that a mixture of traditional manufacturing methods and additive methods will be critical to building a colony on Mars.

Imagine for instance that you want to build some buildings. Lets say both pouring concrete and additive manufacturing methods would work. You need to build 40 habitats. Would you rather work all day in a space suit in the hazardous near vacuum of Mars to build the forms needed to pour concrete for the structures? Or sit in your pajamas in a habitat on a computer designing and controlling the robots that will do it for you? And in that case, maybe you will want to have the robots make forms and pour the concrete for you, but perhaps you will use additive manufacturing methods.

I can imagine the latter is easier for robots, and using robots is easier for humans than doing the labor themselves.

Of course, to build a robot that will manufacture a home out of concrete, you need to build the mechanical parts of that robot. How will you do that? Probably not with CNC machines and blocks of aluminum (making such parts was my job for 7 years BTW). Instead I imagine that you will keep a library of feedstocks for 3D printing and you will print out the robot parts in your lab.

Interesting fact: there are now some extremely high performance plastics available for common home-style 3D printers, including carbon fiber filled PEEK. At $850 per kg that's a material I don't think you'd use unless you had to, but if I were building a colony on Mars at $500k a head I think I'd bring 100kg of that stuff.

100kg of carbon fiber filled PEEK plastic will make a lot of concrete extruding habitat constructing robot frames.

You'll have to bring the motors and electronics separately. At least until you build that foundry....

See what I mean when I say 3D printing can help make a self sustaining economy possible?