diff --git a/EXE_GdbCreateSurf.cpp b/EXE_GdbCreateSurf.cpp
index 8860e87..a2e351a 100644
--- a/EXE_GdbCreateSurf.cpp
+++ b/EXE_GdbCreateSurf.cpp
@@ -503,6 +503,11 @@ MyCreateSurfTmConvexHullInBBox( int nParentId, int nId, const BBox3d& b3Box, int
    vTria[1] = MyCreateSidePlaneHull( vVert, bNXp, b3Box, -3) ;
    vTria[2] = MyCreateSidePlaneHull( vVert, bNXp, b3Box, +2) ;
    vTria[3] = MyCreateSidePlaneHull( vVert, bNXp, b3Box, -2) ;
+  // invalido i triangoli con normale opposta alla direzione attesa
+   for ( int i = 0 ; i < 4 ; ++ i) {
+      if ( ( vTria[i].GetN().x > 0) != bNXp)
+         vTria[i].Set( vTria[i].GetP( 0), vTria[i].GetP( 1), vTria[i].GetP( 2)) ;
+   }
   // cerco uno o due piani validi
    int nPlane1 = -1 ;
    int nPlane2 = -1 ;
diff --git a/EgtExecutor.rc b/EgtExecutor.rc
index a83652d..7dbecaa 100644
Binary files a/EgtExecutor.rc and b/EgtExecutor.rc differ