diff --git a/MachMgrRawParts.cpp b/MachMgrRawParts.cpp
index a015c25..2cc14ac 100644
--- a/MachMgrRawParts.cpp
+++ b/MachMgrRawParts.cpp
@@ -376,6 +376,10 @@ MachMgr::AddRawPart( int nSurfId, Color cCol)
    int nRawGroupId = GetCurrRawGroupId() ;
    if ( nRawGroupId == GDB_ID_NULL)
       return GDB_ID_NULL ;
+  // verifico che la superficie sia chiusa
+   const ISurf* pSurf = GetSurf( m_pGeomDB->GetGeoObj( nSurfId)) ;
+   if ( pSurf == nullptr  ||  ! pSurf->IsClosed())
+      return GDB_ID_NULL ;
   // recupero l'ingombro della superficie in globale
    BBox3d b3Surf ;
    if ( ! m_pGeomDB->GetGlobalBBox( nSurfId, b3Surf))
@@ -407,7 +411,7 @@ MachMgr::AddRawPart( int nSurfId, Color cCol)
       if ( IsNull( pCrvCompo))
          return GDB_ID_NULL ;
      // recupero la superficie trimesh
-      ISurfTriMesh* pStm = GetSurfTriMesh( m_pGeomDB->GetGeoObj( nId)) ;
+      const ISurfTriMesh* pStm = GetSurfTriMesh( m_pGeomDB->GetGeoObj( nId)) ;
       if ( pStm == nullptr)
          return GDB_ID_NULL ;
      // recupero l'ingombro della superficie in locale