How to create .stl file?
Click Output tab - Send panel -Export.
In the Export Data dialog box, enter a file name.
Under Files of Type, select Lithography (*.stl). Click Save.
Select one or more solid objects. All objects must be entirely within the
positive XYZ octant of the world coordinate system (WCS). That is, their X, Y, and Z coordinates must be greater than zero.
The file extension .stl is automatically appended to the file name.