diff --git a/Operation.cpp b/Operation.cpp
index 3c6a667..f513a27 100644
--- a/Operation.cpp
+++ b/Operation.cpp
@@ -29,7 +29,7 @@
 #include "/EgtDev/Include/EGkIntersCurves.h"
 #include "/EgtDev/Include/EGkIntersLineSurfTm.h"
 #include "/EgtDev/Include/EGkGeomDB.h"
-#include "/EgtDev/Include/EGkCDeBoxPolyhedron.h"
+#include "/EgtDev/Include/EGkCDeBoxClosedSurfTm.h"
 #include "/EgtDev/Include/EXeConst.h"
 #include "/EgtDev/Include/EgtPointerOwner.h"
 
@@ -2197,8 +2197,9 @@ Operation::TestCollisionAvoid( const DBLVECTOR& vAxStart, const DBLVECTOR& vAxEn
    INTVECTOR vCollId ;
    pMch->GetCurrHeadCollGroups( vCollId) ;
   // distanza di sicurezza
+   const double MIN_SAFEDIST = 10.0 ;
    double dSafeDist = m_pMchMgr->GetCurrMachiningsMgr()->GetSafeZ() ;
-   dSafeDist = min( dSafeDist, max( 0.5 * dSafeDist, 10.0)) ;
+   dSafeDist = min( dSafeDist, max( 0.5 * dSafeDist, MIN_SAFEDIST)) ;
   // Vado nelle posizioni da controllare
    const int COLL_STEP = 16 ;
    bool bCollide = false ;
@@ -2240,11 +2241,13 @@ Operation::TestCollisionAvoid( const DBLVECTOR& vAxStart, const DBLVECTOR& vAxEn
                  // sottobox testa nel riferimento del solido
                   BBox3d b3Hsol ;
                   m_pGeomDB->GetRefBBox( biSH.second, frSolid, b3Hsol) ;
-                  b3Hsol.Expand( dSafeDist) ;
+                  Point3d ptMin ;
+                  Vector3d vtDiag ;
+                  b3Hsol.GetMinDim( ptMin, vtDiag.x, vtDiag.y, vtDiag.z) ;
                  // solido
                   const ISurfTriMesh* pStm = GetSurfTriMesh( m_pGeomDB->GetGeoObj( nRawSolidId)) ;
                  // verifica di collisione tra sottobox e solido
-                  if ( pStm == nullptr  ||  CDeBoxPolyhedron( b3Hsol, *pStm)) {
+                  if ( pStm == nullptr  ||  CDeBoxClosedSurfTm( Frame3d( ptMin), vtDiag, dSafeDist, *pStm)) {
                      bCollide = true ;
                      break ;
                   }