I would grind the excess of the sides, the advantage being that by working the whole edge you avoid overheating. A cutting disc might be quicker , but all the heating is in one place.

Other tricks include wrapping damp rag round the file, using damp sand to hold the file. Above all, take your time by alternating with another job – grind a bit, do somehting else while it cools, grind a bit, repeat.

Martin

…and consider climb milling onto the face you are creating rather than off it. That way any burrs will not affect the bottom (or top), cutting edge(s) of the file.

As a few Dreadnought's are available, I'd experiment with one. Might be easy to soften and re-harden with heat. Depends on the steel.

Older files were mostly made from plain Carbon Tool steel. Workable when the metal annealed, and going up to glass hard when quenched, usually in water or brine, not oil. Quenching in Brine makes steel extra hard, but the result may be too brittle. All that's needed is a decent fire, or big torch, and a drum full of salt water. Fire-scale is avoided by keeping the item in a non-oxidising part of the fire.

Try heating a file cherry-red throughout, hold for about one minute per cubic inch of metal, and then allow it to cool slowly. Should soften the metal making it easier to mill, file, grind or linish to shape. Then reheat to cherry-red, make sure the metal is all the same colour, and plunge and stir into the brine drum. (Lots of brine needed – at least a bucketful.) Although the process is simple, there's a fair bit of skill in it – judging cherry-red for example.

With luck the steel will re-harden. Won't if the file is made of HSS, because several precise and long-winded steps are needed to harden it properly. A modern file might well be made of HSS because it's tougher than tool-steel and less likely to snap.

My experience suggests Silver Steel is best for amateur hardening. Tolerant of misjudgements, though not completely idiot-proof! Yes, I have failed to harden Silver Steel.

Dave