diff --git a/LuaLibs/ProcessProfConcave.lua b/LuaLibs/ProcessProfConcave.lua
index a95315a..ab9ea43 100644
--- a/LuaLibs/ProcessProfConcave.lua
+++ b/LuaLibs/ProcessProfConcave.lua
@@ -150,8 +150,8 @@ function ProcessProfConcave.Make( Proc, nPhase, nRawId, nPartId, dCurrOvmH)
          EgtSetMachiningParam( MCH_MP.INVERT, true)
       end
       -- se lavorazione a destra da dietro o sinistra di fronte, inverto
-      if  ( vtN:getX() > 0 and vtN:getY() > 0.1) or
-          ( vtN:getX() < 0 and vtN:getY() < -0.1) then
+      if  ( bHead and vtN:getY() > 0.1) or
+          ( not bHead and vtN:getY() < -0.1) then
          EgtSetMachiningParam( MCH_MP.WORKSIDE, MCH_MILL_WS.LEFT)
          EgtSetMachiningParam( MCH_MP.INVERT, true)
       end
diff --git a/LuaLibs/ProcessProfConvex.lua b/LuaLibs/ProcessProfConvex.lua
index 69e0fee..87e9dd8 100644
--- a/LuaLibs/ProcessProfConvex.lua
+++ b/LuaLibs/ProcessProfConvex.lua
@@ -150,8 +150,8 @@ function ProcessProfConvex.Make( Proc, nPhase, nRawId, nPartId, dCurrOvmH)
          EgtSetMachiningParam( MCH_MP.INVERT, true)
       end
       -- se lavorazione a destra da dietro o sinistra di fronte, inverto
-      if  ( vtN:getX() > 0 and vtN:getY() > 0.1) or
-          ( vtN:getX() < 0 and vtN:getY() < -0.1) then
+      if  ( bHead and vtN:getY() > 0.1) or
+          ( not bHead and vtN:getY() < -0.1) then
          EgtSetMachiningParam( MCH_MP.WORKSIDE, MCH_MILL_WS.LEFT)
          EgtSetMachiningParam( MCH_MP.INVERT, true)
       end