diff --git a/src/Mod/OpenSCAD/OpenSCADFeatures.py b/src/Mod/OpenSCAD/OpenSCADFeatures.py
index ec71a1425..977c30225 100644
--- a/src/Mod/OpenSCAD/OpenSCADFeatures.py
+++ b/src/Mod/OpenSCAD/OpenSCADFeatures.py
@@ -306,6 +306,7 @@ class GetWire:
 
     def execute(self, fp):
         if fp.Base:
+            import Part
             #fp.Shape=fp.Base.Shape.Wires[0]
             fp.Shape=Part.Wire(fp.Base.Shape.Wires[0]) # works with 0.13 stable
             #sh = fp.Base.Shape.Wires[0].copy; sh.transformSahpe(fp.Base.Shape.Placement.toMatrix()); fp.Shape = sh #untested
@@ -348,6 +349,8 @@ class Frustum:
                 pts.append(pts[0])
                 shape = Part.makePolygon(pts)
                 face = Part.Face(shape)
+                if ir==1: #top face
+                    face.reverse()
                 wires.append(shape)
                 faces.append(face)
             #shellperi=Part.makeRuledSurface(*wires)
@@ -438,12 +441,12 @@ class OffsetShape:
 
     def onChanged(self, fp, prop):
         pass
-        #if prop in ["Offset"]:
-        #    self.createGeometry(fp)
+        if prop in ["Offset"]:
+            self.createGeometry(fp)
 
     def createGeometry(self,fp):
         if fp.Base and fp.Offset:
-            fp.Shape=fp.Base.Shape.makeOffsetShape(self.Offset,1e-6)
+            fp.Shape=fp.Base.Shape.makeOffsetShape(fp.Offset,1e-6)
 
 def makeSurfaceVolume(filename):
     import FreeCAD,Part
diff --git a/src/Mod/OpenSCAD/OpenSCADUtils.py b/src/Mod/OpenSCAD/OpenSCADUtils.py
index d9e7c63a9..646cfb69a 100644
--- a/src/Mod/OpenSCAD/OpenSCADUtils.py
+++ b/src/Mod/OpenSCAD/OpenSCADUtils.py
@@ -29,6 +29,12 @@ This Script includes various pyhton helper functions that are shared across
 the module
 '''
 
+def translate(context,text):
+    "convenience function for Qt translator"
+    from PySide import QtGui
+    return QtGui.QApplication.translate(context, text, None, \
+        QtGui.QApplication.UnicodeUTF8)
+
 class OpenSCADError(Exception):
     def __init__(self,value):
         self.value= value
@@ -342,10 +348,13 @@ def process3D_ObjectsViaOpenSCAD(doc,ObjList,Operation):
         return(obj)
 
 def process_ObjectsViaOpenSCAD(doc,children,name):
-    if all(obj.Shape.Volume == 0 for obj in children):
+    if all((not obj.Shape.isNull() and obj.Shape.Volume == 0) \
+            for obj in children):
         return process2D_ObjectsViaOpenSCAD(children,name)
-    elif all(obj.Shape.Volume > 0 for obj in children):
+    elif all((not obj.Shape.isNull() and obj.Shape.Volume > 0) \
+            for obj in children):
         return process3D_ObjectsViaOpenSCAD(doc,children,name)
     else:
+        import FreeCAD
         FreeCAD.Console.PrintError( unicode(translate('OpenSCAD',\
-            "Error Both shapes must be either 2D or both must be 3D"))+u'\n')
+            "Error all shapes must be either 2D or both must be 3D"))+u'\n')
diff --git a/src/Mod/OpenSCAD/importCSG.py b/src/Mod/OpenSCAD/importCSG.py
index 8118fb301..caf062a1c 100644
--- a/src/Mod/OpenSCAD/importCSG.py
+++ b/src/Mod/OpenSCAD/importCSG.py
@@ -47,6 +47,7 @@ import ply.yacc as yacc
 import Part
 
 from OpenSCADFeatures import RefineShape 
+from OpenSCADFeatures import Frustum
 #from OpenSCAD2Dgeom import *
 from OpenSCADUtils import *
 isspecialorthogonaldeterminant = isspecialorthogonalpython
@@ -360,6 +361,8 @@ def CGALorPlaceholder(name,children,arguments=[]):
     '''Tries to perform a CGAL opertion by calling scad
     if it fails it creates a placeholder object to continue parsing
     '''
+    if any(obj.Shape.isNull() for obj in children):
+        doc.recompute() #we need valid shapes
     newobj = process_ObjectsViaOpenSCAD(doc,children,name)
     if newobj is not None :
         return newobj
@@ -434,7 +437,10 @@ def fuse(lst,name):
     global doc
     if printverbose: print "Fuse"
     if printverbose: print lst
-    if len(lst) == 1:
+    if len(lst) == 0:
+        myfuse = doc.addObject("Part::Feature","emptyfuse")
+        myfuse.Shape  = Part.Compound([])
+    elif len(lst) == 1:
        return lst[0]
     # Is this Multi Fuse
     elif len(lst) > 2:
@@ -468,7 +474,10 @@ def p_difference_action(p):
     if printverbose: print "difference"
     if printverbose: print len(p[5])
     if printverbose: print p[5]
-    if (len(p[5]) == 1 ): #single object
+    if (len(p[5]) == 0 ): #nochild
+        mycut = doc.addObject("Part::Feature","emptycut")
+        mycut.Shape  = Part.Compound([])
+    elif (len(p[5]) == 1 ): #single object
         p[0] = p[5]
     else:
 # Cut using Fuse    
@@ -499,7 +508,7 @@ def p_intersection_action(p):
        if gui:
            for subobj in mycommon.Shapes:
                subobj.ViewObject.hide()
-    else :
+    elif (len(p[5]) == 2):
        if printverbose: print "Single Common"
        mycommon = doc.addObject('Part::Common',p[1])
        mycommon.Base = p[5][0]
@@ -507,7 +516,11 @@ def p_intersection_action(p):
        if gui:
            mycommon.Base.ViewObject.hide()
            mycommon.Tool.ViewObject.hide()
-
+    elif (len(p[5]) == 1):
+        mycommon = p[5][0]
+    else : # 1 child
+        mycommon = doc.addObject("Part::Feature","emptyintersection")
+        mycommon.Shape  = Part.Compound([])
     p[0] = [mycommon]
     if printverbose: print "End Intersection"
 
@@ -792,13 +805,13 @@ def p_cylinder_action(p):
     r1 = float(p[3]['r1'])
     r2 = float(p[3]['r2'])
     n = int(p[3]['$fn'])
+    fnmax = FreeCAD.ParamGet(\
+        "User parameter:BaseApp/Preferences/Mod/OpenSCAD").\
+        GetInt('useMaxFN')
     if printverbose: print p[3]
     if ( r1 == r2 and r1 > 0):
         if printverbose: print "Make Cylinder"
-        fnmax = FreeCAD.ParamGet(\
-            "User parameter:BaseApp/Preferences/Mod/OpenSCAD").\
-            GetInt('useMaxFN')
-        if n < 3 or fnmax != 0 and n >= fnmax:
+        if n < 3 or fnmax != 0 and n > fnmax:
             mycyl=doc.addObject("Part::Cylinder",p[1])
             mycyl.Height = h
             mycyl.Radius = r1
@@ -829,13 +842,25 @@ def p_cylinder_action(p):
                 mycyl.Height  = h
 
     elif (r1 != r2):
-        if printverbose: print "Make Cone"
-        mycyl=doc.addObject("Part::Cone",p[1])
-        mycyl.Height = h
-        mycyl.Radius1 = r1
-        mycyl.Radius2 = r2
+        if n < 3 or fnmax != 0 and n > fnmax:
+            if printverbose: print "Make Cone"
+            mycyl=doc.addObject("Part::Cone",p[1])
+            mycyl.Height = h
+            mycyl.Radius1 = r1
+            mycyl.Radius2 = r2
+        else:
+            if printverbose: print "Make Frustum"
+            mycyl=doc.addObject("Part::FeaturePython",'frustum')
+            Frustum(mycyl,r1,r2,n,h)
+            if gui:
+                if FreeCAD.ParamGet("User parameter:BaseApp/Preferences/Mod/OpenSCAD").\
+                    GetBool('useViewProviderTree'):
+                    from OpenSCADFeatures import ViewProviderTree
+                    ViewProviderTree(mycyl.ViewObject)
+                else:
+                    mycyl.ViewObject.Proxy = 0
     else: # r1 == r2 == 0
-    	FreeCAD.Console.PrintWarning('cylinder with radius zero\n')
+        FreeCAD.Console.PrintWarning('cylinder with radius zero\n')
         mycyl=doc.addObject("Part::Feature","emptycyl")
         mycyl.Shape = Part.Compound([])
     if printverbose: print "Center = ",tocenter
diff --git a/src/Mod/OpenSCAD/prototype.py b/src/Mod/OpenSCAD/prototype.py
index 86c49d6d7..a73cabe1c 100644
--- a/src/Mod/OpenSCAD/prototype.py
+++ b/src/Mod/OpenSCAD/prototype.py
@@ -140,8 +140,8 @@ class Node:
                     obj.Height  = h
                     if self.arguments['center']:
                         center(obj,0,0,h)
-                    base.ViewObject.hide()
-                elif True: #use Frustum Feature with makeRuledSurface
+                    #base.ViewObject.hide()
+                elif False: #use Frustum Feature with makeRuledSurface
                     obj=doc.addObject("Part::FeaturePython",'frustum')
                     Frustum(obj,r1,r2,int(self.arguments['$fn']),h)
                     ViewProviderTree(obj.ViewObject)