diff --git a/LuaLibs/CalcPaths.lua b/LuaLibs/CalcPaths.lua
index 5826def..c7686af 100644
--- a/LuaLibs/CalcPaths.lua
+++ b/LuaLibs/CalcPaths.lua
@@ -1496,7 +1496,7 @@ local function CalcRibsPaths( nSliceGrp, nRibsGrp, LayerParams, nIdx, vPtStart)
       local nSrfExt = EgtGetFirstNameInGroup( nCrvGrp, LAYER_SRF) or GDB_ID.NULL
       
       -- trim grossolano dei setti
-      local nTrimGrp = TrimRibs( vOrigRibs, nRibsGrp, nSrfExt, LayerParams.dOffs + LayerParams.dStrand, LayerParams.vtSlicing)
+      local nTrimGrp = TrimRibs( vOrigRibs, nRibsGrp, nSrfExt, LayerParams.dOffs - LayerParams.dStrand / 2, LayerParams.vtSlicing)
     
       -- calcolo offset orientati
       local nOffsGrp = ComputeRibsOrientedOffset( nTrimGrp, LayerParams.dStrand)