diff --git a/VolZmapVolume.cpp b/VolZmapVolume.cpp
index 79411f9..1930c68 100644
--- a/VolZmapVolume.cpp
+++ b/VolZmapVolume.cpp
@@ -1765,6 +1765,7 @@ VolZmap::Comp_5AxisMilling( int nGrid, const Point3d& ptS, const Point3d& ptE, c
    Vector3d vtDirTip = ptP2T - ptP1T ;
    bool bTopIsPivot = vtDirTop.IsSmall() ;
    bool bTipIsPivot = vtDirTip.IsSmall() ;
+   bool bSmallMovement = vtDirTop.Len() < 10 * EPS_SMALL  &&  vtDirTip.Len() < 10 * EPS_SMALL ;
    bool bInverse = ! (bTopIsPivot || bTipIsPivot)  &&  vtDirTop * vtDirTip < 0 ;
 
    if ( bInverse)
@@ -1857,26 +1858,44 @@ VolZmap::Comp_5AxisMilling( int nGrid, const Point3d& ptS, const Point3d& ptE, c
    }
 
    vector<PNTVECTOR> vvPtCtrl ;
-   // superficie laterale sinistra
-   CurveLine cLineLeftBottom ; cLineLeftBottom.Set( vPntTipEndFront.back(), vPntTipStartFront.back()) ;
-   if ( bInverse)
-      cLineLeftBottom.Invert() ;
-   PtrOwner<CurveBezier> cBezLeftBottom( GetBasicCurveBezier( LineToBezierCurve( &cLineLeftBottom, nDegU, bRat))) ;
-   CurveLine cLineLeftTop ; cLineLeftTop.Set( vPntTopEndFront.back(), vPntTopStartFront.back()) ;
-   PtrOwner<CurveBezier> cBezLeftTop( GetBasicCurveBezier( LineToBezierCurve( &cLineLeftTop, nDegU, bRat))) ;
-   vvPtCtrl.emplace_back( cBezLeftBottom->GetAllControlPoints()) ;
-   PNTVECTOR vPntLeft = cBezLeftTop->GetAllControlPoints() ;
-   vvPtCtrl.back().insert( vvPtCtrl.back().end(), vPntLeft.begin(), vPntLeft.end()) ;
-   // superficie laterale destra
-   CurveLine cLineRightBottom ; cLineRightBottom.Set( vPntTipStartFront.front(), vPntTipEndFront.front()) ;
-   if ( bInverse)
-      cLineRightBottom.Invert() ;
-   PtrOwner<CurveBezier> cBezRightBottom( GetBasicCurveBezier( LineToBezierCurve( &cLineRightBottom, nDegU, bRat))) ;
-   CurveLine cLineRightTop ; cLineRightTop.Set( vPntTopStartFront.front(), vPntTopEndFront.front()) ;
-   PtrOwner<CurveBezier> cBezRightTop( GetBasicCurveBezier( LineToBezierCurve( &cLineRightTop, nDegU, bRat))) ;
-   vvPtCtrl.emplace_back( cBezRightBottom->GetAllControlPoints()) ;
-   PNTVECTOR vPntRight = cBezRightTop->GetAllControlPoints() ;
-   vvPtCtrl.back().insert( vvPtCtrl.back().end(), vPntRight.begin(), vPntRight.end()) ;
+   if ( ! bSmallMovement) {
+      // superficie laterale sinistra
+      CurveLine cLineLeftBottom ; cLineLeftBottom.Set( vPntTipEndFront.back(), vPntTipStartFront.back()) ;
+      if ( ! cLineLeftBottom.IsValid())
+         return false ;
+      if ( bInverse)
+         cLineLeftBottom.Invert() ;
+      PtrOwner<CurveBezier> cBezLeftBottom( GetBasicCurveBezier( LineToBezierCurve( &cLineLeftBottom, nDegU, bRat))) ;
+      if ( IsNull( cBezLeftBottom))
+         return false ;
+      CurveLine cLineLeftTop ; cLineLeftTop.Set( vPntTopEndFront.back(), vPntTopStartFront.back()) ;
+      if ( ! cLineLeftTop.IsValid())
+         return false ;
+      PtrOwner<CurveBezier> cBezLeftTop( GetBasicCurveBezier( LineToBezierCurve( &cLineLeftTop, nDegU, bRat))) ;
+      if ( IsNull( cBezLeftTop))
+         return false ;
+      vvPtCtrl.emplace_back( cBezLeftBottom->GetAllControlPoints()) ;
+      PNTVECTOR vPntLeft = cBezLeftTop->GetAllControlPoints() ;
+      vvPtCtrl.back().insert( vvPtCtrl.back().end(), vPntLeft.begin(), vPntLeft.end()) ;
+      // superficie laterale destra
+      CurveLine cLineRightBottom ; cLineRightBottom.Set( vPntTipStartFront.front(), vPntTipEndFront.front()) ;
+      if ( ! cLineRightBottom.IsValid())
+         return false ;
+      if ( bInverse)
+         cLineRightBottom.Invert() ;
+      PtrOwner<CurveBezier> cBezRightBottom( GetBasicCurveBezier( LineToBezierCurve( &cLineRightBottom, nDegU, bRat))) ;
+      if ( IsNull( cBezRightBottom))
+         return false ;
+      CurveLine cLineRightTop ; cLineRightTop.Set( vPntTopStartFront.front(), vPntTopEndFront.front()) ;
+      if ( ! cLineRightTop.IsValid())
+         return false ;
+      PtrOwner<CurveBezier> cBezRightTop( GetBasicCurveBezier( LineToBezierCurve( &cLineRightTop, nDegU, bRat))) ;
+      if ( IsNull( cBezRightTop))
+         return false ;
+      vvPtCtrl.emplace_back( cBezRightBottom->GetAllControlPoints()) ;
+      PNTVECTOR vPntRight = cBezRightTop->GetAllControlPoints() ;
+      vvPtCtrl.back().insert( vvPtCtrl.back().end(), vPntRight.begin(), vPntRight.end()) ;
+   }
    if ( nSub == 1) {
       // superficie inferiore
       vvPtCtrl.emplace_back( PNTVECTOR( { vPntTipStartFront.front(), vPntTipStartFront.back(), vPntTipEndFront.front(), vPntTipEndFront.back() })) ;
@@ -2116,7 +2135,7 @@ VolZmap::Comp_5AxisMilling( int nGrid, const Point3d& ptS, const Point3d& ptE, c
       vvPtCtrl.emplace_back( cBezTipEndF2->GetAllControlPoints()) ;
       PNTVECTOR vPntEndF2 = cBezTopEndF2->GetAllControlPoints() ;
       vvPtCtrl.back().insert( vvPtCtrl.back().end(), vPntEndF2.begin(), vPntEndF2.end()) ;
-      if ( bInverse) {
+      if ( bInverse  ||  bSmallMovement) {
          // chiudo il volume con le superici verticali end back 1
          vvPtCtrl.emplace_back( cBezTipEndB1->GetAllControlPoints()) ;
          PNTVECTOR vPntEndB1 = cBezTopEndB1->GetAllControlPoints() ;
@@ -2135,7 +2154,7 @@ VolZmap::Comp_5AxisMilling( int nGrid, const Point3d& ptS, const Point3d& ptE, c
       vvPtCtrl.emplace_back( cBezTipStartB2->GetAllControlPoints()) ;
       PNTVECTOR vPntStartB2 = cBezTopStartB2->GetAllControlPoints() ;
       vvPtCtrl.back().insert( vvPtCtrl.back().end(), vPntStartB2.begin(), vPntStartB2.end()) ;
-      if ( bInverse) {
+      if ( bInverse   ||  bSmallMovement) {
          // chiudo il volume con le superici verticali start front 1
          vvPtCtrl.emplace_back( cBezTipStartF1->GetAllControlPoints()) ;
          PNTVECTOR vPntStartF1 = cBezTopStartF1->GetAllControlPoints() ;
@@ -2215,7 +2234,7 @@ VolZmap::Comp_5AxisMilling( int nGrid, const Point3d& ptS, const Point3d& ptE, c
    }
 
    // inizializzo le superfici bilineari e i parametri per le intersezioni
-   for ( int z = 0 ; z < int( vvPtCtrl.size()) ; ++z) {
+   for ( int z = 0 ; z < ssize( vvPtCtrl) ; ++z) {
       vSurfBez[nSurfInd].sBez.Init( nDegU, nDegV, nSpanU, nSpanV, bRat) ;
       vSurfBez[nSurfInd].sBez.SetControlPoint( 0, vvPtCtrl[z][0]) ;
       vSurfBez[nSurfInd].sBez.SetControlPoint( 1, vvPtCtrl[z][1]) ;