diff --git a/SurfFinishing.cpp b/SurfFinishing.cpp
index 258d251..4c08499 100644
--- a/SurfFinishing.cpp
+++ b/SurfFinishing.cpp
@@ -1388,9 +1388,9 @@ SurfFinishing::AddZigZag( ICAvToolSurfTm* pCAvTlStm, const Frame3d& frSurf,
                while ( currPU != vPntU.end()) {
                   auto nextPU = next( currPU) ;
                   bool bNext = ( nextPU != vPntU.end()) ;
-                  bool bNextDown = ( bNext ? nextPU->second > -m_Params.m_dApprox : true) ;
+                  bool bNextDown = ( bNext ? nextPU->second < m_Params.m_dApprox : true) ;
                  // punto corrente è al minimo
-                  if ( currPU->second > -m_Params.m_dApprox) {
+                  if ( currPU->second < m_Params.m_dApprox) {
                     // se precedente e successivo al minimo, cancello e basta
                      if ( bPrevDwn  &&  bNextDown) {
                         if ( ! ptPrev.IsValid()  ||  abs( currPU->first.y - ptPrev.y) > 10 * EPS_SMALL)
@@ -1855,9 +1855,9 @@ SurfFinishing::AddOneWay( ICAvToolSurfTm* pCAvTlStm, const Frame3d& frSurf,
                while ( currPU != vPntU.end()) {
                   auto nextPU = next( currPU) ;
                   bool bNext = ( nextPU != vPntU.end()) ;
-                  bool bNextDown = ( bNext ? nextPU->second > -m_Params.m_dApprox : true) ;
+                  bool bNextDown = ( bNext ? nextPU->second < m_Params.m_dApprox : true) ;
                  // punto corrente è al minimo
-                  if ( currPU->second > -m_Params.m_dApprox) {
+                  if ( currPU->second < m_Params.m_dApprox) {
                     // se precedente e successivo al minimo, cancello e basta
                      if ( bPrevDwn  &&  bNextDown) {
                         if ( ! ptPrev.IsValid()  ||  abs( currPU->first.y - ptPrev.y) > 10 * EPS_SMALL)
@@ -2744,7 +2744,7 @@ SurfFinishing::GetLastGoodPoint( ICAvToolSurfTm* pCAvTlStm, const Frame3d& frSur
    auto currPU = lstPntU.begin() ;
    while ( ! bFound  &&  currPU != lstPntU.end()) {
       auto nextPU = next( currPU) ;
-      if ( nextPU == lstPntU.end()  ||  nextPU->second < -m_Params.m_dApprox){
+      if ( nextPU == lstPntU.end()  ||  nextPU->second > m_Params.m_dApprox){
          bFound = true ;
          ptP1 = GetToGlob( currPU->first - vtToolL * m_TParams.m_dLen, frSurf) ;
       }
diff --git a/SurfRoughing.cpp b/SurfRoughing.cpp
index 89b04b7..f42eb1e 100644
--- a/SurfRoughing.cpp
+++ b/SurfRoughing.cpp
@@ -1236,8 +1236,10 @@ SurfRoughing::ProcessPath( int nPathId, int nTempId, int nPvId, int nClId)
       }
       Frame3d frPlanes ;
       frPlanes.Set( plPlane.GetPoint(), vtTool) ;
-      const double SILH_TOL = 0.5 ;
-      CAvParSilhouettesSurfTm cavParSilh( vpStm, frPlanes, SILH_TOL) ;
+      const double SILH_TOL = 1.0 ;
+      PtrOwner<ICAvParSilhouettesSurfTm> pCavParSilh( CreateCAvParSilhouettesSurfTm()) ;
+      if ( IsNull( pCavParSilh)  ||  ! pCavParSilh->SetData( vpStm, frPlanes, SILH_TOL))
+         return false ;
 
      // calcolo le regioni di svuotatura alle varie quote come differenza tra regioni da lavorare e regioni di silhouette
       INTVECTOR vPocket ;
@@ -1341,7 +1343,7 @@ SurfRoughing::ProcessPath( int nPathId, int nTempId, int nPvId, int nClId)
         /* *************************** Silhouette **************************** */
         // determino la regione da non lavorare e la sottraggo
          POLYLINEVECTOR vPL ;
-         if ( ! cavParSilh.GetSilhouette( ( it->second).dDepth - GetOffsL(), vPL)) {
+         if ( ! pCavParSilh->GetSilhouette( ( it->second).dDepth - GetOffsL(), vPL)) {
             m_pMchMgr->SetLastError( 3024, "Error in SurfRoughing : region not computable") ;
             return false ;
          }