Extruding a square curve?

I work for a welding shop that has 3 robots. I program the tool paths for them in Rhino. We scan dies and then regenerate them back to the CAD model. In this particular case we are going to weld 1/2 inch solid steel stock to the dies border, where the weld border would be. So that we are certain that the die has enough material to be milled back down to spec. I’ve already scanned the die, before the stock is welding on. So, in the past I just drew a surface with a distance of 1/2 inch past the top of my mesh. As I’ve gotten better in Rhino, I’ve began to get more creative in my mesh modifications. That’s the case now, I want to essentially add the same dimensional solid as that square stock getting welded on. Sooo… I researched… And ultimately believe the command “ExtrudeCrvAlongCrv” made the most sense. I drew my square curve around the surface of my mesh, offset it by a quarter of an inch. Drew a 1/2 in square perpendicular and equally distributed from the curves center and tried the command. Didn’t really work at all…

My question… How do I do this? Is the above command the best route? I thought about doing my normal surface add and then extruding it down 1 inch through the mesh and the splitting the two. Suggestions?

Hello- Sweep1 is more likely what you want, I’d say.