deegc
I attempted to reply to your question, but the garden web system booted me out after two attempts to make my post acceptable. In hind sight, I realize that the name of one type of file I was recommending apparently tripped off a smut filter.

The message I got was that I was using html code, which I wasn't, or profanity, which I wasn't.

So drop me an email, and I'll reply directly with my advice.

Just use sandpaper. Copper is soft enough that woodworking tools work just fine. I used a random orbit sander with 200 grit to round out my corners and edges, but you could do it by hand as well. The Gator grit brand works great.