Die Filer From Bar Stock With Video and Plans

[Toolmaker51]

Ideally, a die filer uses "parallel machine files", and shank is at the end to produce a cut on the down stroke. In general, needle files aren't a bad alternative, long as you are not working into an acute corner, where tapered shapes will bind. It's a lot like band sawing, best results are with three or more teeth engaged in the cut. Files are more forgiving, teeth meet material at an angle.
When I started, die-filers were the only practical way to generate corners in a die, and taper beneath the cutting section, known as 'die-life'. Way before EDM, many contours were roughed out on a vertical band saw to start with; provided shop was equipped with a band saw welder...