diff --git a/MachMgrOperations.cpp b/MachMgrOperations.cpp
index 8622d99..46043d3 100644
--- a/MachMgrOperations.cpp
+++ b/MachMgrOperations.cpp
@@ -1124,7 +1124,16 @@ MachMgr::RemovePreviewMachiningTool( void) const
 int
 MachMgr::GetPreviewMachiningToolStepCount( void) const
 {
-   return -1 ;
+  // recupero la lavorazione corrente
+   int nCurrMchId = GetCurrMachining() ;
+   if ( nCurrMchId == GDB_ID_NULL)
+      return 0 ;
+  // ne recupero il gestore
+   Machining* pMch = GetMachining( m_pGeomDB->GetUserObj( nCurrMchId)) ;
+   if ( pMch == nullptr)
+      return 0 ;
+  // eseguo
+   return pMch->GetToolPreviewStepCount() ;
 }
 
 //----------------------------------------------------------------------------
diff --git a/Machining.cpp b/Machining.cpp
index c7ecaad..11393f6 100644
--- a/Machining.cpp
+++ b/Machining.cpp
@@ -178,7 +178,36 @@ Machining::RemoveToolPreview( void) const
 int
 Machining::GetToolPreviewStepCount( void) const
 {
-   return -1 ;
+  // verifico validità gestori DB geometrico e CAM
+   if ( m_pGeomDB == nullptr  ||  m_pMchMgr == nullptr)
+      return 0 ;
+  // recupero gruppo per geometria di lavorazione (Cutter Location)
+   int nClId = m_pGeomDB->GetFirstNameInGroup( GetOwner(), MCH_CL) ;
+   if ( nClId == GDB_ID_NULL)
+      return 0 ;
+  // determino il numero di entità di tutti i sottogruppi, escludendo CLIMB e RISE
+   int nCount = 0 ;
+   int nPxId = m_pGeomDB->GetFirstGroupInGroup( nClId) ;
+   while ( nPxId != GDB_ID_NULL) {
+     // aggiungo tutte le entità del truppo
+      nCount += m_pGeomDB->GetGroupObjs( nPxId) ;
+     // tolgo le entità CLIMB
+      int nClimbId = m_pGeomDB->GetFirstNameInGroup( nPxId, MCH_CL_CLIMB) ;
+      while ( nClimbId != GDB_ID_NULL) {
+         -- nCount ;
+         nClimbId = m_pGeomDB->GetNextName( nClimbId, MCH_CL_CLIMB) ;
+      }
+     // tolgo le entità RISE
+      int nRiseId = m_pGeomDB->GetFirstNameInGroup( nPxId, MCH_CL_RISE) ;
+      while ( nRiseId != GDB_ID_NULL) {
+         -- nCount ;
+         nRiseId = m_pGeomDB->GetNextName( nRiseId, MCH_CL_RISE) ;
+      }
+     // passo al successivo sottogruppo
+      nPxId = m_pGeomDB->GetNextGroup( nPxId) ;
+   }
+
+   return nCount ;
 }
 
 //----------------------------------------------------------------------------
@@ -270,11 +299,29 @@ Machining::ToolPreview( int nEntId, int nStep) const
       nParentId =  m_pGeomDB->GetParentId( nEntId) ;
       if ( m_pGeomDB->GetParentId( nParentId) == nClId) {
         // se richiesta successiva
-         if ( nStep > 0)
-            nEntId = GetToolPreviewNext( m_pGeomDB, nEntId, nParentId) ;
+         if ( nStep > 0) {
+            while ( nStep > 0) {
+               int nOldId = nEntId ;
+               nEntId = GetToolPreviewNext( m_pGeomDB, nEntId, nParentId) ;
+               -- nStep ;
+               if ( nEntId == GDB_ID_NULL) {
+                  nEntId = nOldId ;
+                  break ;
+               }
+            }
+         }
         // se richiesta precedente
-         else if ( nStep < 0)
-            nEntId = GetToolPreviewPrev( m_pGeomDB, nEntId, nParentId) ;
+         else if ( nStep < 0) {
+            while ( nStep < 0) {
+               int nOldId = nEntId ;
+               nEntId = GetToolPreviewPrev( m_pGeomDB, nEntId, nParentId) ;
+               ++ nStep ;
+               if ( nEntId == GDB_ID_NULL) {
+                  nEntId = nOldId ;
+                  break ;
+               }
+            }
+         }
       }
       else
          nEntId = GDB_ID_NULL ;