Production steps of LIOGIER Hand-stitched Rasps
For over 100 years, LIOGIER has been producing high-quality hand-stitched rasps in the Auvergne Region of France. At one time, although almost unknown outside of France, it was the largest producer of these tools in Europe.
The production takes place over four steps: forging, forming, cutting, and hardening. Every step requires a great deal of experience and careful attention to detail in order to produce these rasps renowned for their quality of cut.
At the beginning one needs a high-quality, appropriate steel: LIOGIER uses exclusively a specially alloyed high carbon steel.
The raw steel is heated to 1250° so that it can be formed and forged.
This is done by swaging: it is the only method that can guarantee the integrity and uniformity of the steel’s structure, and much reduces the chance of introducing faults like airpockets or folds in the raw blank.
The process also guarantees the compression of the steel in relation to the form of the file blank to produce a grain orientation providing an extremely high mechanical strength.
2) The design and preparation of the file blank’s surface: the goal is a perfect shape.
First the raw blank is ground, then polished with an unusually fine grit, and then it is ready for the finishing. At every step the quality of the final product depends on the skill and experience of the toolmakers to exactly produce the desired form and finish.
When, for instance the surface is uneven or insufficiently polished, the quality of the rasp will be reduced because the required sharpness cannot be achieved.
3) Hand cutting the teeth: a unique skill.
The shaped and polished blank is clamped on the workbench and the rasp cutter, working toward daylight, stamps out one tooth after another by eye and by feel.
Training a rasp cutter takes 2 years, and it can take an experienced worker up to 90 minutes to cut the teeth.
At this step, there can be no false moves. If the cutter misses his strike, the blank must be scrapped and the process started again with a fresh one. But the result is well worth the trouble. These rasps and rifflers are among the finest of their kind and cannot be reproduced using mass production techniques with machines.
A century of experience is incorporated into this process. The secret is to heat the fully-formed file to exactly 805° C, and then it is quenched in a salt water bath. This sudden cooling results in an optimal hardness for the teeth. The heart of the process lies in the composition and heat-dispersing characteristics of the salt water, as opposed to water or oil, which are also used for quenching.
After the heat treatment, the rasps are cleaned and carefully inspected. They then get an anti-corrosion coating, and the tool is finally finished, except for installation of the handles and packaging.
Hand-cut rasps function differently from machine cut rasps. They cut faster and leave a surprising good surface because of the excellent surface quality, extra sharpness, and the slightly irregular spacing of their teeth.
The cutting geometry of the teeth on these rasps is oriented so that they cut best when used by a right-handed person.
The tooth sizes are numbered from 1 to 15, with 1 being the coarsest, and 15 the finest. In practice, only the sizes between 4 and 14 are commonly used.