diff --git a/VolZmapVolume.cpp b/VolZmapVolume.cpp
index 5a86031..3558439 100644
--- a/VolZmapVolume.cpp
+++ b/VolZmapVolume.cpp
@@ -863,6 +863,8 @@ GetCylMoveRotBBox( const Point3d& ptP1, const Point3d& ptP2, const Vector3d& vtV
 
    Vector3d vtDirTop = ptP2 - ptP1 ;
    Vector3d vtDirTip = ptP2T - ptP1T ;
+   vtDirTop.Normalize() ;
+   vtDirTip.Normalize() ;
 
   // determino i punti laterali del top e del bottom(tip), nella posizione di partenza
    Vector3d vtAuxTopS = vtV1 ^ vtDirTop ;