Making a file is not unduly difficult. It does involve some specialized skill, though. A very sharp, specially ground chisel to raise line burrs across the width of the file blank is required. The file blank needs be high carbon plain steel at minimum. Lower grades of steel may be used with case hardening (actually through carborization of the burrs). Depending on the metalurgy of the blank, heat treating can be farily simple to rather complex. This day and age, files are more or less a commodity item. I once observed one of Purdey's workmen profiling a barrel with a hand/purpose made file gifted to him by his gaffer.
DDA
