diff --git a/SlidingSurface3D/rfpm.geo b/SlidingSurface3D/rfpm.geo
index 0aadd5b0ee2a4c1f09d39682de4afc702d58493d..28eb4eb56042854e657c513fd970c56890e5acd2 100644
--- a/SlidingSurface3D/rfpm.geo
+++ b/SlidingSurface3D/rfpm.geo
@@ -124,12 +124,12 @@ Function Volume2Cube
   //
   // input: Volumes()
   // output: cube()
-  points() = PointsOf{ Volume{ Volumes() }; };
-  point() = Point { points(0) };
+  _points() = PointsOf{ Volume{ Volumes() }; };
+  point() = Point { _points(0) };
   Call ChangeCoordinates;
   cube() = {coord(0), coord(1), coord(2), coord(0), coord(1), coord(2)};
-  For p In {1 : #points() - 1}
-    point() = Point{ points(p) };
+  For p In {1 : #_points() - 1}
+    point() = Point{ _points(p) };
     Call ChangeCoordinates;
     cube(0) = (coord(0) < cube(0) ? coord(0) : cube(0));
     cube(1) = (coord(1) < cube(1) ? coord(1) : cube(1));
@@ -146,30 +146,30 @@ Function Cube2Face
   //
   // input: cube() and FaceId
   // output: face()
-  bbox() = cube();
-  bbox(Modulo(FaceId + 3, 6)) = bbox(FaceId);
+  _bbox() = cube();
+  _bbox(Modulo(FaceId + 3, 6)) = _bbox(FaceId);
   face() = {};
-  surfaces() = Boundary{ Volume{ Volumes() }; };
-  For s In { 0:#surfaces()-1 }
+  _surfaces() = Boundary{ Volume{ Volumes() }; };
+  For s In { 0:#_surfaces()-1 }
     NbIn = 0;
-    points() = PointsOf { Surface { surfaces(s) } ; };
-    For p In { 0 : #points() - 1 }
-      point() = Point { points(p) };
+    _points() = PointsOf { Surface { _surfaces(s) } ; };
+    For p In { 0 : #_points() - 1 }
+      point() = Point { _points(p) };
       Call ChangeCoordinates;
       If((CoordinateSystem == 1) && (coord(0) == 0))
-        coord(1) = bbox(1);
+        coord(1) = _bbox(1);
       EndIf
-      If((coord(0) > bbox(0) - tol) &&
-         (coord(1) > bbox(1) - tol) &&
-         (coord(2) > bbox(2) - tol) &&
-         (coord(0) < bbox(3) + tol) &&
-         (coord(1) < bbox(4) + tol) &&
-         (coord(2) < bbox(5) + tol))
+      If((coord(0) > _bbox(0) - tol) &&
+         (coord(1) > _bbox(1) - tol) &&
+         (coord(2) > _bbox(2) - tol) &&
+         (coord(0) < _bbox(3) + tol) &&
+         (coord(1) < _bbox(4) + tol) &&
+         (coord(2) < _bbox(5) + tol))
         NbIn++;
       EndIf
     EndFor
-    If(NbIn == #points())
-      face() += surfaces(s);
+    If(NbIn == #_points())
+      face() += _surfaces(s);
     EndIf
   EndFor
 Return
@@ -206,10 +206,26 @@ StatorPerSlave() = face();
 FaceId = 5; Call Cube2Face;
 StatorTop() = face();
 
-// The width of the air ring region is arbitrary, but it is in general thin, 
+// The width of the air ring region is arbitrary, but it is in general thin,
 // especially in machine models where it has to fit into the air gap.
 
-surfaces() = Boundary { Volume{10}; };
+// get boundary surfaces of the air ring by geometric identifiying, in order to
+// distinguish lateral surfaces from the top and bottom
+Volumes() = {10}; Call Volume2Cube;
+surfaces() = {};
+FaceId = 0; Call Cube2Face;
+surfaces() += face();
+FaceId = 1; Call Cube2Face;
+surfaces() += face();
+FaceId = 2; Call Cube2Face;
+surfaces() += face();
+FaceId = 3; Call Cube2Face;
+surfaces() += face();
+FaceId = 4; Call Cube2Face;
+surfaces() += face();
+FaceId = 5; Call Cube2Face;
+surfaces() += face();
+
 lines() = Boundary { Surface{ SlidingSlave() }; };
 For num In { 0:#surfaces()-1 }
   lines() += Boundary { Surface{ surfaces(num) }; };
@@ -233,9 +249,10 @@ For num In { 0:#lines()-1 }
   EndIf
 EndFor
 
-  //Transfinite Surface{ surfaces() } ;
-Transfinite Surface{ SlidingMaster() } ;
+Transfinite Surface{ surfaces() } ;
+Recombine Surface{ surfaces({1,2,4,5}) };
 Transfinite Surface{ SlidingSlave() } ;
+Transfinite Volume { 10 };
 
 // Identify 'SlidingSubmaster' Curve
 
diff --git a/SlidingSurface3D/rfpm_common.pro b/SlidingSurface3D/rfpm_common.pro
index 7eacae2fb86aaf19dd5add0e3d0a2279ac63bca9..80a155ba73087345d229462168e43c2080d7078e 100644
--- a/SlidingSurface3D/rfpm_common.pro
+++ b/SlidingSurface3D/rfpm_common.pro
@@ -8,7 +8,7 @@ If(lc <= 0)
 EndIf
 
 // Number of elements on the sliding surface in rotation direction
-NbrDiv = 50*mm/lc;
+NbrDiv = 100*mm/lc;
 
 ModelAngleMin = 0. ;
 ModelAngleMax = 60. ;