I'm using a round copper wire of 1.3 mm in diameter. Have to bend very carefully, in small steps. I cut flat (not round) area within the helix.
I love working with a metal handle hammer - it is quite, well absorbs vibration and shock. Hammer with a wooden handle is also good, but I like less.
We need to knock gently to evenly flattened wire. Step-by-step. Take your time - then we will have the edge is equable.
I tap with a hammer just the reverse side. Thus the front side will be as smooth as mirror.
The sharp edges of the wire is required to smooth out needle files.