I have bought a Prusa i3 to learn the basics of 3D printing with, and have used Rhino on and off in the past for some modelling.

I've got the machine printing quite well now, but have just used simple calibration models downloaded here and there.

My first simple design was a plain box, open topped, 160x55x25mm roughly with 3mm wall thickness. A bit like a supe simple cattle water trough if you like.

Using Repetier and Slic3r, when I loaded it it said there were difficulties, and when sliced just produced a solid box with huge amounts of lines and layers!

I modelled it in Rhino 4, and saved it as an .stl

Am I doing something basically wrong? Or will Rhino not make good .stl files?