diff --git a/SurfRoughing.cpp b/SurfRoughing.cpp
index 8cde5e4..b759032 100644
--- a/SurfRoughing.cpp
+++ b/SurfRoughing.cpp
@@ -1491,7 +1491,7 @@ SurfRoughing::ProcessPath( int nPathId, int nPvId, int nClId)
 
      // costruisco una superficie di estrusione della curva (devo determinare parte della regione limite)
       Vector3d vtLimitExtr = - vtTool * 1.5 * max( b3Raw.GetDimX(), max( b3Raw.GetDimY(), b3Raw.GetDimZ())) ;
-      PtrOwner<ISurfTriMesh> pStmLimit( GetStmOutSideSfr( pSfrSgro, pStmRaw, vtLimitExtr)) ;
+      PtrOwner<ISurfTriMesh> pStmLimit( GetStmOutSideSfr( pSfrSgro, dDepth, pStmRaw, vtLimitExtr)) ;
       if ( IsNull( pStmLimit))
          return false ;
 
@@ -2095,7 +2095,7 @@ SurfRoughing::GetRaw( void) const
 
 //----------------------------------------------------------------------------
 ISurfTriMesh*
-SurfRoughing::GetStmOutSideSfr( const ISurfFlatRegion* pSfr, const ISurfTriMesh* pStmRaw, const Vector3d& vtExtr) const
+SurfRoughing::GetStmOutSideSfr( const ISurfFlatRegion* pSfr, double dDepth, const ISurfTriMesh* pStmRaw, const Vector3d& vtExtr) const
 {
   // controllo dei parametri
    if ( pSfr == nullptr  ||  !  pSfr->IsValid()  ||
@@ -2134,7 +2134,10 @@ SurfRoughing::GetStmOutSideSfr( const ISurfFlatRegion* pSfr, const ISurfTriMesh*
   // box della superficie piana
    BBox3d BBoxSfr ;
    bOk = bOk && pSfrOffs->GetLocalBBox( BBoxSfr) ;
-   BBoxSfr.Expand( 0., 0., vtExtr.Len()) ;
+   double dExtraX = abs( dDepth * ( pSfrOffs->GetNormVersor() * X_AX)) ;
+   double dExtraY = abs( dDepth * ( pSfrOffs->GetNormVersor() * Y_AX)) ;
+   double dExtraZ = abs( dDepth * ( pSfrOffs->GetNormVersor() * Z_AX)) ;
+   BBoxSfr.Expand( dExtraX, dExtraY, dExtraZ) ;
   // scorro le parts
    for ( int nPart = 0 ; nPart < pStmLimit->GetPartCount() && bOk ; ++ nPart) {
      // calcolo il box della part corrente
@@ -2142,7 +2145,7 @@ SurfRoughing::GetStmOutSideSfr( const ISurfFlatRegion* pSfr, const ISurfTriMesh*
       bOk = bOk && pStmLimit->GetPartLocalBBox( nPart, BBoxPart) ;
      // se non c'è intersezione con i Box, elimino la parte corrente
       BBox3d BBoxInt ;
-      if ( BBoxSfr.FindIntersection( BBoxPart, BBoxInt)) {
+      if ( ! BBoxSfr.FindIntersection( BBoxPart, BBoxInt)) {
          bOk = pStmLimit->RemovePart( nPart) ;
          -- nPart ;
       }
diff --git a/SurfRoughing.h b/SurfRoughing.h
index d6eb165..1d3f90b 100644
--- a/SurfRoughing.h
+++ b/SurfRoughing.h
@@ -130,7 +130,7 @@ class SurfRoughing : public Machining
       bool AddLeadOut( const Point3d& ptEnd, const Vector3d& vtEnd, const Vector3d& vtN,
                        const ICurveComposite* pRCrv, bool bSplitArcs, bool bNoneForced, Point3d& ptP1) ;
       ISurfTriMesh* GetRaw( void) const ;
-      ISurfTriMesh* GetStmOutSideSfr( const ISurfFlatRegion* pSfr, const ISurfTriMesh* pStmRaw, const Vector3d& vtExtr) const ;
+      ISurfTriMesh* GetStmOutSideSfr( const ISurfFlatRegion* pSfr, double dDepth, const ISurfTriMesh* pStmRaw, const Vector3d& vtExtr) const ;
       ISurfFlatRegion* GetSfrByStmIntersection( const IntersParPlanesSurfTm& IPPStm, double dDist, double dSmallOffs = 0) const ;
       ISurfFlatRegion* GetSfrSilhouette( ICAvParSilhouettesSurfTm* pCavParSilh, double dDepth, double Sil_tol, bool& bOk) const ;
       bool GetActiveSurfaces( INTVECTOR& vSurfId, INTVECTOR& vSurfSuppId) const ;