>>8706331>3d printing surfacesIt depends. The big thing is layer height:
These days some filament(FDM) printers can print very thin layers, however the printing time goes up proportionally to the total number of layers in the print.
At their best, they look smooth from a distance or under most lightings when seen in person. Sometimes the layer lines are actually fine and aligned enough that they cause slight refractive effects on the light reflecting off their surfaces. Up close, most cameras will still be able to make out layer lines though.
Tactilely they can often feel fairly smooth, but not quite the shear glass surface levels of smooth, that is possible with injection molded plastic.
There are also a lot of types of post-processing which can improve the surface finish. Sanding is the most rudimentary, but there are also coatings and epoxies that can go on the surface of prints, and I think even ways to melt the surface more together using either heat or possibly chemical treatments.
SLA and DLP (use light to selectively cure liquid resin) (Pic related was made with this type of printing) printers can make parts which are completely smooth to anything less than a microscope, assuming you have the time and ability to set them to print that finely.
However they have their own unique concerns, such as ventilation, curing, and the differing tolerances and other material properties of the resins compared to those of the various types of filament plastics.
