diff --git a/LuaLibs/CalcSlices.lua b/LuaLibs/CalcSlices.lua
index eb12a26..60295bb 100644
--- a/LuaLibs/CalcSlices.lua
+++ b/LuaLibs/CalcSlices.lua
@@ -441,6 +441,11 @@ function CalcSlices.Exec( nPartId, nStmId, HMax)
       local nSurfFR, nSrfNbr = EgtSurfFlatRegion( nLayId, vClosedId)
 
       if nSurfFR then
+         -- verifico orientamento della normale
+         local vtN = EgtSurfFrNormVersor( nSurfFR, GDB_ID.ROOT)
+         if AreOppositeVectorApprox( vtN, vtSlicing) then
+            EgtInvertSurf( nSurfFR)
+         end
          -- elimino le curve originali
          for i = 1, #vClosedId do
             EgtErase( vClosedId[i])