diff --git a/LuaLibs/WProcessLapJoint.lua b/LuaLibs/WProcessLapJoint.lua
index 371b113..9bd0daa 100644
--- a/LuaLibs/WProcessLapJoint.lua
+++ b/LuaLibs/WProcessLapJoint.lua
@@ -2020,11 +2020,13 @@ local function MakeSideGrooveByMill( Proc, nFacet, nRawId, b3Raw, sCustomMach, d
          dStepOri = dStep
          if dStep < GEO.EPS_SMALL then dStep = 0.75 * dMaxMat end
          local nStep = ceil( ( dThick - dMaxMat) / dStep)
-         dStep = max( ( dThick - dMaxMat) / max( nStep, 1), 0)
-         local dMaxElev = max( ( nStep + 1) * dStep - GEO.EPS_SMALL, 0)
-         -- tasca aperta sopra non necessita di MaxElev
+         local dMaxElev
+         -- tasca aperta sopra non necessita di MaxElev e mantiene lo step originale
          if Proc.Fct == 2 and Proc.AffectedFaces.Top then
             dMaxElev = nil
+         else
+            dStep = max( ( dThick - dMaxMat) / max( nStep, 1), 0)
+            dMaxElev = max( ( nStep + 1) * dStep - GEO.EPS_SMALL, 0)
          end
          if nSinglePass and nSinglePass > 0 then
             dStep = 0