I see you've got the job done now, but I was going to suggest one idea that I've been eyeballing at HF. They have a small table-mount grinder/polisher that also has a removable side attachment like the Dremel pen-style extension. Kind of a kill three birds with one stone kind of deal. The whole setup is $30-$40.
I like the bur bits like qslim suggested. For metals, I really like this bit. It's cutting isn't as violent as the bur bits, and makes for a much smoother cut.
https://www.amazon.com/dp/B00004UDJJ/?tag=wranglerorg-20
I read through and realized I was overthinking it too. Hand files! I bought a set of files from Lowe's that I later found a very similar set at HF. Those are a great set of tools to have on hand.
https://www.lowes.com/pd/Project-Source-23-Piece-File-Set/4777065
I like the bur bits like qslim suggested. For metals, I really like this bit. It's cutting isn't as violent as the bur bits, and makes for a much smoother cut.
https://www.amazon.com/dp/B00004UDJJ/?tag=wranglerorg-20
I read through and realized I was overthinking it too. Hand files! I bought a set of files from Lowe's that I later found a very similar set at HF. Those are a great set of tools to have on hand.
https://www.lowes.com/pd/Project-Source-23-Piece-File-Set/4777065