IMPROVEMENTS IN RENEWING THE TEETH OF FILES
Year: 1853

page_text: LETTERS PATENT to Emile Grillet, of Soho Square, in the County
of Middlesex, Gentleman, for the Invention of "IMPROVEMENTS IN
RENEWING THE TEETH OF FILES."
Sealed the 5th July 1858, and dated the 6th January 1858.
PROVISIONAL SPECIFICATION left by the said Emile Grillet at
the Office of the Commissioners of Patents, with his Petition,
on the 6th January 1858.
I, EMILE GRILLET, of. Soho Square, in the County of Middlesex, do
hereby declare the nature of the said Invention for "IMPROVEMENTS
IN RENEWING THE TEETH OF FILES" to be as follows:-
My Invention of improvements in renewing the teeth of files has
reference to the application of acid for that purpose, the biting action of
which on the metal deepens the grooves and sharpens the cutting
edges of the teeth, whereby worn out files are again rendered fit
for use.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said Emile Grillet in the Great Seal Patent Office,
on the 6th July 1853.
TO ALL TO WHOM THESE PRESENTS SHALL COME, 1,
EMILE GRILLET, of Soho Square, in the County of Middlesex, Gentle-
mien, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Sixth day of January, in the, year of
our Lord One thousand eight hundred and fifty-three, in the sixteenth
year of Her reign, did, for Herself, Eler heirs and successors, give and
grant unto me, the said Emile Grillet, Her special licence that I,
the said Emile Grillet, my executors, administrators, and assigns, or
such others as I, the said Emile Grillet, my executors, administra
tors, and assigns, should at any time agree with, and no others, from
time to time and at all times thereafter during the term therein ex-
pressed, should and lawfully might make, use, exercise, and vend,
within the United Kingdom of Great Britain and Ireland, the Channel
Islands, and Isle of Man, an Invention for "IMPROVEMENTS IN RENEWING
THE TEETH OF FILES," upon the condition (amongst others) that I, the said
Emile Grillet, by an instrument in writing under my hand and seal,
should particularly describe and ascertain the nature of the said Inven-
tion, and in what manner the same was to be performed, and cause the
same to be filed in the Great Seal Patent Office within six calendar
months next and immediately after the date of the said Letters Patent.
NOW KNOW YE, that I, the said Emile Grillet, do hereby declare
the nature of my said Invention, and in what manner the same is to
be performed, to be particularly described and ascertained in and by
the following statement (that is to say):
My Invention of improvements in renewing the teeth of files relates
to sharpening the teeth of files that have become worn out from use,
and which I effect by the application of a corrosive agent to the surface
of the file. The constant attrition to which a file is subject gradually
reduces and blunts the accuminated points constituting its cutting
surface, and in order to again render the file of service I restore such

page_text: accuminated points of the teeth, giving it the appearance and rendering
it serviceable as a new file. I renew the teeth by the action of an
acid, and in order that such acid will take proper and uniform effect I
previously remove any grease or dirt from the surface of the file in the
following manner :-
I prepare a bath of unslaked lime and potash in the following pro-
portions: I take one pound of lime, and mix it with two pounds of
potash in one gallon of water, stirring the whole intimately together,
and allowing it to remain until three fourths of the liquid has passed
off by evaporation. The remaining fourth of a gallon of supernatant
liquor is then drawn off, and when quite cold is adapted to receive the
files to be cleansed.
The files to be treated, after having any superabundance of greasy
matter roughly rubbed of, are immersed in the liquor described; and
allowed to remain four hours therein. It is advisable that the files
should be placed in a stand or rack, or otherwise disposed 'so that the
fluid may act freely thereon. The files having remained four hours in
the bath, after which they are removed and brushed, and subsequently
cleansed in clean water. In order to permit the proper action of the
acid to which the files are to be subjected it is essential the whole
greasy matter should be removed in the cleansing process.
Having thoroughly cleansed the files to be operated upon by the
acid, I immerse them in a dilute mixture of sulphuric acid in the pro-
portion of about one part of sulphuric acid to two parts of water, using
it more or less dilute according to circumstances hereafter explained.
Common water may be used to dilute the acid, but I prefer distilled
water for this purpose. The vessel containing the acid I prefer to be
rectangular, and lined with or of such material as is not 'or only slightly
affected by the acid, such as lead or glass, or other vitrious or earthen
substance. A stand or rack is fitted to the vessel to receive the files,
which are held in a vertical position, and so lisposed that the acid will
act freely throughout the entire surface immersed, and so that the
liquid has free access between the several files. The biting action of
the acid attacks the whole surface of the files immersed, the continued

page_text: effect of which gradually deepens the several cavities between the
cutting points of the teeth, which become accuminated and sharp as they
were originally. In preparing the acid the bath must be allowed to
cool before the files are immersed.
The action of the acid is continued for a longer or shorter period of
time according to the character of the file; for a fine or smooth file, an im-
mersion of about three hours will be sufficient for the purpose, but for files
of a coarser kind, that is, with less numerous and larger teeth, will require
from five to six hours. The time will, however, depend upon the strength
of the acid used for the purpose. The strength of the acid may be
varied according to the character of the files; as for fine files it
should be in no case stronger than the proportions before given, and
may even be weaker with advantage, but which will of course take a
longer time to perform its office. For coarser files, that is, with large,
teeth, the strength of the acid must be increased in proportion. During
the period of immersion the files should be withdrawn five or six times,
plunged into clean water, and brushed in order to disengage and
remove from the surface of its acute interior angles the oxide of iron
produced, which adheres thereto. This, if allowed to remain, impedes
the action of the acid, and would render the operation imperfect, as the
files would be more acted upon at one point than another, and would
leave the projecting points of the teeth more exposed to the acid than
the base of such teeth.
In order to prevent as much as possible the adhesion or deposit of
the oxide of iron detached from the file by the acid I place the files in
a vertical position in the bath as before mentioned, with their points
downwards, so that the angles of the teeth present as little obstruction
as possible to the oxide falling away from the surface of the file, and
becoming precipitated in the bath; some of it, however, will adhere,
and must be removed by brushing as described.
I before mentioned that the bath was rectangular, which is simply
for the convenience of apportioning the acid to the several files to be
immersed at one time, so that they shall be subject to a uniform action
of the acid, for which purpose the stand by which they are sustained

page_text: must be made so as to keep them at regular distances, and distribute
them equally throughout the bath of acid. A stand or rack of wood I
find answers the purpose, as it is not acted on by the acid. The inter-
stices in which the files are placed and sustained must be such that the
acid has free access to the file. To insure this, it is better to support
this stand entirely above the fluid, and allow the files to rest on the
bottom of the bath, on a piece of wood placed there, with small cavities
for receiving the points of the files.
I have mentioned sulphuric acid as that which I employ as being
better for commercial use, but other acids will answer the purpose;
nitric, azotic, and other acids attack iron, but I prefer sulphuric acid as
being efficient and cheap. In treating files according to my Invention
it is not necessary to soften them before subjecting them to the action
of the acid, as it will have its due effect upon the teeth in the hard as
in the soft state; but where files have been previously softened, or
partially so, it becomes necessary to select such, and re-harden them
after renewing the teeth, which hardening is performed in the ordinary
manner, as well understood.
By this process of renewing the teeth of files the teeth which have
been blunted by use become sharpened, but it must be observed that
where the teeth have become detached they cannot of course be
replaced. This will not be the case with the finer descriptions of files,
or files used with a proper degree of care, and which when renewed by
this process present all the appearance and usefulness of a new file. An
advantage in this mode of renewing files, in addition to its being com-
paratively inexpensive, is, that the least possible weight of metal is
removed from the file, whereas by the ordinary process of file cutting
the whole of the old teeth must be removed to accomplish the re-cutting,
which so reduces the file that it is at once detected, and cannot, except
in fine files, he re-cut more than once; but by the foregoing process the
renewing may be repeated several times, and is so inexpensive as to
render it of advantage to wear the files much less than usual before
renewing.
Having described the nature of my Invention, I would have it under-
stood that I do not confine myself to the precise mode of proceeding

page_text: before set forth, which may be varied according to circumstances; but
what I claim as my Invention is, renewing the teeth of files by the
action of acid, substantially as described.
In witness whereof, 1, the said Emile Grillet, have hereunto set
my hand and seal, this Sixth day of July One thousand eight
hundred and fifty-three.
Witness,
WILLIAM CLARK,
53, Chancery Lane.
EMILE GRILLET. (L.S.)