Splines and tool paths - having trouble (unexpected behavior)

[GregHeumann]

I posted this over on the Manufacturing forum but I realize it should be here:

I have a goal of being able to design slot patterns for my microphone grills using splines. I have already been successful generating tool paths from sketches based on sketch slots, extruded into the grill body. 
 
I tried the same technique with some splines (both single line sketches I hoped could become a tool path, and contours from multiple connected splines)  but I FAILED MISERABLY so I went to a very simple experiment. I created a rectangle, extruded it. I sketched the top rectangle with the rectangle tool, the middle one with 4 straight spline lines and the bottom shape with the slot tool. Extruded each.
In Manufacturing, using the 2D Slot tool, it works as expected on the top rectangle and the bottom slot but it refuses to accept the center (spline-defined) rectangle. (I AM able to select it and it previews exactly the same as the other pockets.) But it says "Invalid Contours". 

What am I not getting?

[davebYYPCU]

Your right would be better in Manufacture area, that I can’t speak to, 

There would be a good? reason a rectangle created with four splines, would work for you, but I don’t think it is so efficient.  Perhaps contoured spline walls would trigger a response for the tool paths, maybe Fusion rejects straight splines in Manufacture, where lines are expected.

Might help....