earliest metal rasps were made by the aid of hammer and punch,
the earliest files by a hammer having chisel edge, and later by
chisel and hammer.
Records exist to show that steel was used for
files as early as the twelfth century, and that this steel was
often of case-hardened type, the core being left soft.
The file was forged to shape on the anvil, given
the desired dimensions, flattened, and the teeth cut by the
chisel-edged hammer. The file was then hardened by a rather
primitive form of heat-treatment, ox-horn being used as the
carbonaceous substance that gave the steel its surface hardness.
After case-carburizing in this manner, the file
was quenched in water. For smaller files goats’ leather was used
as the carburizing medium.
The hammer used in earliest ages for cutting
files had a double edge, and was shaped roughly as in the image
above. Exceptional skill was needed for its use, and in no
circumstances can the teeth by it have had the precision and
regularity even of the hand-cut file made by the employment of
hammer and chisel.
Eventually, as will be imagined, the superior control over the
spacing and direction of the teeth given by the hammer and
chisel method led to its world-wide adoption, and it persisted
right down to modern times.
from "Steel File" by Eric N.
Simons, (London: Isaac Pitman & Sons, LTD., 1947.)
The image of German File Cutter
is from the
“House books of the Nuremberg 12 Brothers Foundation” Project.