diff --git a/ToolsMgr.cpp b/ToolsMgr.cpp
index c65f1fb..e2a7261 100644
--- a/ToolsMgr.cpp
+++ b/ToolsMgr.cpp
@@ -688,8 +688,12 @@ ToolsMgr::GetCurrToolMaxDepth( double dSafe, double& dMaxDepth) const
          GetValInNotes( m_tdCurrTool.m_sSysNotes, TSI_THLEN, dTHoldLen) ;
          GetValInNotes( m_tdCurrTool.m_sSysNotes, TSI_THDIAM, dTHoldDiam) ;
       }
-     // calcolo il massimo affondamento
-      dMaxDepth = m_tdCurrTool.m_dLen - ( m_tdCurrTool.m_dDiam > dTHoldDiam ? 0 : dTHoldLen) - dSafe ;
+     // calcolo il massimo affondamento (lunghezza TH negativa significa che TH è parte della testa)
+      dMaxDepth = m_tdCurrTool.m_dLen - dSafe ;
+      if ( m_tdCurrTool.m_dDiam > dTHoldDiam)
+         dMaxDepth -= min( 0., dTHoldLen) ;
+      else
+         dMaxDepth -= max( 0., dTHoldLen) ;
       return true ;
    }
   // se mortasatrice o sega a catena