diff --git a/LuaLibs/CalcPaths.lua b/LuaLibs/CalcPaths.lua
index 76e91c0..3dd6dcf 100644
--- a/LuaLibs/CalcPaths.lua
+++ b/LuaLibs/CalcPaths.lua
@@ -979,7 +979,7 @@ end
 --------------------------------------------------------------------
 local function UpdateTotalShellSurf( nSrf, nCrv, dStrand, nGrpId)
    
-   local nCopyCrv = EgtCopyGlob( nCrv, nGrpId)
+   --[[local nCopyCrv = EgtCopyGlob( nCrv, nGrpId)
    -- creo percorso chiuso corrispondente
    if not EgtCurveIsClosed( nCrv) then
       local nCopy2 = EgtCopyGlob( nCrv, nGrpId)
@@ -1000,17 +1000,29 @@ local function UpdateTotalShellSurf( nSrf, nCrv, dStrand, nGrpId)
    end
    
    local nSrfExtraShell = EgtSurfFlatRegion( nGrpId, vSrfIds)
+   
    if not EgtSurfFrSubtract( nSrf, nSrfExtraShell) then
       EgtInvertSurf( nSrfExtraShell)
       EgtSurfFrSubtract( nSrf, nSrfExtraShell)
    end
-  
-   EgtErase( nCopyCrv)
-   for i = 1, #vSrfIds do
-      EgtErase( vSrfIds[i])
+   --EgtErase( nCopyCrv)
+   --for i = 1, #vSrfIds do
+   --   EgtErase( vSrfIds[i])
+   --end
+   --EgtErase( nSrfExtraShell)
+   ]]--
+
+   local nSrfExtraShell = EgtSurfFrFatCurve( nGrpId, nCrv, dStrand + s_dOffsCorr, false)
+   if nSrfExtraShell then
+      local vtSrfN = EgtSurfFrNormVersor( nSrf, GDB_ID.ROOT)
+      local vtSrfExShN = EgtSurfFrNormVersor( nSrfExtraShell, GDB_ID.ROOT)
+      if vtSrfExShN * vtSrfN < 0 then
+         EgtInvertSurf( nSrfExtraShell)
+      end
+      EgtSurfFrSubtract( nSrf, nSrfExtraShell)
+      EgtErase( nSrfExtraShell)
    end
-   EgtErase( nSrfExtraShell)
-   
+
 end
 
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