diff --git a/CamData.cpp b/CamData.cpp
index 61a2754..a2d284e 100644
--- a/CamData.cpp
+++ b/CamData.cpp
@@ -349,7 +349,7 @@ CamData::GetDrawPolyLines( POLYLINELIST& lstPL) const
       PL.AddUPoint( 1, ptTip) ;
      // aggiungo simil-freccia
       Frame3d frF ;
-      if ( m_vtTool. IsSmall())
+      if ( m_vtTool. IsSmall()  ||  AreSameOrOppositeVectorApprox( m_vtTool, m_vtCorr))
          frF.Set( ptTip, m_vtCorr) ;
       else
          frF.Set( ptTip, m_vtCorr, m_vtTool) ;
@@ -378,7 +378,7 @@ CamData::GetDrawPolyLines( POLYLINELIST& lstPL) const
       PL.AddUPoint( 1, ptTip) ;
      // aggiungo simil-freccia
       Frame3d frF ;
-      if ( m_vtTool. IsSmall())
+      if ( m_vtTool. IsSmall()  ||  AreSameOrOppositeVectorApprox( m_vtTool, m_vtAux))
          frF.Set( ptTip, m_vtAux) ;
       else
          frF.Set( ptTip, m_vtAux, m_vtTool) ;
diff --git a/GeoCalc.cpp b/GeoCalc.cpp
index 6ca4d62..2f0aa47 100644
--- a/GeoCalc.cpp
+++ b/GeoCalc.cpp
@@ -82,7 +82,7 @@ GetRotationComponent( const Vector3d& vtDir1, double dComp, const Vector3d& vtDi
    double dDenom = dT0uv * dSinG ;
    double dNumer = dComp - dT0w * dCosG ;
    // due angoli possibili
-   if ( abs( dDenom) > abs( dNumer)) {
+   if ( abs( dDenom) > abs( dNumer) + SIN_EPS_ANG_ZERO) {
       double dDeltaAngRad = acos( dNumer / dDenom) ;
       dAng1Deg = ( dOffsAngRad + dDeltaAngRad) * RADTODEG ;
       dAng2Deg = ( dOffsAngRad - dDeltaAngRad) * RADTODEG ;
diff --git a/MachineCalc.cpp b/MachineCalc.cpp
index 13369ce..ff32903 100644
--- a/MachineCalc.cpp
+++ b/MachineCalc.cpp
@@ -1009,7 +1009,7 @@ Machine::GetMyAngles( const Vector3d& vtDirT, const Vector3d& vtDirA,
   // calcolo primo angolo di rotazione per seconda soluzione
    bool bDet2 = true ;
    if ( nStat == 2) {
-      if ( ! vtDirH2.GetRotation( vtDirTn, vtAx1, dAngA2, bDet2) )
+      if ( ! vtDirH2.GetRotation( vtDirTn, vtAx1, SIN_EPS_ANG_SMALL, dAngA2, bDet2))
          nStat = 1 ;
       else {
         // se indeterminato, provo a determinarlo con la direzione ausiliaria
@@ -1032,7 +1032,7 @@ Machine::GetMyAngles( const Vector3d& vtDirT, const Vector3d& vtDirA,
   // calcolo primo angolo di rotazione per prima soluzione
    bool bDet1 = true ;
    if ( nStat >= 1) {
-      if ( ! vtDirH1.GetRotation( vtDirTn, vtAx1, dAngA1, bDet1) )
+      if ( ! vtDirH1.GetRotation( vtDirTn, vtAx1, SIN_EPS_ANG_SMALL, dAngA1, bDet1))
          nStat = 0 ;
       else {
         // se indeterminato, provo a determinarlo con la direzione ausiliaria