Easy method to cut "Fish Mouths"

[graemeian]

I have a lot of thin wall tubing (2.5" OD by .080" wall). I want to cut it in ~24" lengths, clamp it in two vises on a CNC milling center and cut a fish mouth in both ends. I plan to weld these to make a grid structure.
I want to use common tooling. My thought was to put a disc near each end so the vise would not crush the tubing. Now I have the cutting issue. I am looking for a method that would cut the fish mouth fast and efficiently. Does anyone have some good ideas?

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[graemeian]

I ended up using a 2" indexable mill and cut a "U", step down.. another "U"..etc.
It only took about 5 minutes a side.

[hfjbuis]

Make a clamp to hold the tube (2 steel plates, pressed together, turn/drill a hole, mill one side a fraction thinner), put it in a lathe, turn both pipe sides to the requested diameter and (identical) shape.!