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Using the stepdrill, I made a hole big enough for my air driven nibbler to fit and roughed out the shape, about 1/4” from the line.  This is the debut of the new nibbler tool.  I went to Harbor Freight because they had a sale on an air driven 3" cut off tool for $8!!! I got it and saw the nibbler was also on sale for about $20 and I got it too.

I used snips to then get close to the line, and filed the rest of the way.