Files are essential when doing metal work.
They are worth far more than they are sold for.
You have immense amounts of control for fine tuning whatever it is you're building. ¹⁾

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Draw filing is a technique used to shape metal and customarily used with a bastard file.

Clamping the material to be filed in vise:
Clamp your material in the vise with the filing area on a flat plane (ideally horizontal to your body posture).
Hold the file perpendicular to the piece you're working on with 2 hands, one on each end.
Use back and forth strokes only with medium pressure to the surface and it cuts material rather quickly.
Keep each stroke within the same plane each direction. Be careful not to push too hard as you can bend the file or break teeth (use cutting oil or lubricants while filing).
The tang on the file can be held in either hand and the file can be used with either side facing the work piece.

Clamping the file in a vise:
You can put a short piece of plywood or 2×4 in a vice on each side of the file and clamp it in the vise.
You can also use plastic 'soft jaws' to hold the file.
The rest is the same with forward and backward motion on your work piece.
The file has to be held tight. Clamping a file without side protection can ruin the teeth on the sides.

This technique helps achieve, control and maintain square lines, a flat surface and edges better than a grinder.

Draw filing stainless steel with a bastard file 3)

It is essential to clean metal shavings from the file periodically with a wire brush.
Pull the file parallel to the teeth to remove the shavings, oil the teeth and continue.