--- a/stl.py	Thu Apr 06 16:21:21 2017 +0200
+++ b/stl.py	Thu Apr 06 17:18:24 2017 +0200
@@ -2,7 +2,7 @@
 STL related helpers
 """
 
-import os, subprocess, vtk
+import os, subprocess
 import config, data
 
 OPENSCAD_MODULES = """
@@ -36,6 +36,7 @@
     """
     Run openSCAD process, then convert the ascii stl to binary by using vtk
     """
+    import vtk
     if os.path.isfile(output):
         print "skipping existing file %s" % output
         return