Blender has gone through a few changes recently, so I thought I’d give you an update on the STL export process with the new versions (2.6+), as it looks a bit different. You’ll still need to use the older version like 2.49b to export WRL (VRML97) design files, as this isn’t supported in the new versions.
You can get the latest build of Blender here: http://www.blender.org/.
How to export a STL design file using Blender
STL designs are good for all 3D materials.
1. Remove any extra vertices
Select the object and enter Edit mode (Tab). Select all vertices with A, then press W and select "Remove Doubles". This merges any doubled up vertices that are sitting on top of each other.
You can adjust the distance at which vertices are merged by changing the Merge Distance under Mesh tools (press T to show this):
2. Check Triangulation
Blender will triangulate your mesh when you export. Sometimes this can cause issues with smooth or curved parts of your model, so to check to see what it will look like, select all vertices and press CTRL-T.
3. Recalculate Normals
Select all vertices in Edit mode and press CTRL-N and click Recalculate normals outside.
4. Select the object(s) you want to export
Blender will only export the selected objects, so make sure they are highlighted (in object mode).
5. Export to STL
Choose File, Export, Stl (.stl) and save your file: