3D printing a set of hubs (or what ever I think of)

Interesting - why does this happen? And is it possible to make a printer that overcomes this? Or are there post-printing techniques that can be used?

SLS printers work by melting a powder. unfortunately theres always gaps between the powder particles (like balls in a ball pit). some of the gaps disappear (surface tension of the liquid steel pulls it in to the gaps i think?).

considering this, and the surface finish that Screwball brought up, check out the manufacturers example finish, no gaps, pretty darn smooth:

Personally, ive never achieved something like this, so i guess they are heat treating the parts afterwards. when ever i print something it looks like like very fine sandpaper. heat treating isnt off the cards, but i dont actually know anyone at work who does it.