A Method of Sharpening Worn-out Files.
Year: 1893

page_text: Date of Application, 14th Oct., 1893
Complete Specification Left, 12th July, 1894-Accepted, 18th Aug., 1894
PROVISIONAL SPECIFICATION.
A Method of Sharpening Worn-out Files.
I, JAMES ELIJAH BRINDLEY, of Chesterton in the County of Stafford
Engraver, do hereby declare the nature of this invention to be as follows:-
This invention appertains to a method of treating worn out files in such a manner
as to restore the teeth which by use have lost their points and become flat-topped
to their original shape cutting edge, and sharpness and the details of the process by
which I do this are as follows:-
Having first thoroughly cleansed the files I deposit on the flat tops of the teeth
a coating of Brunswick black or other substance which has the property of resisting
the corrosive action of acids, I then immerse the file in a liquid which will corrode
or bite away the steel from those parts (viz. the bottom and sides of the furrows or
grooves between the teeth) which are not protected by the Brunswick black or
other substance used for the purpose. I find the best fluid for this purpose to be
a mixture of nitric acid and water.
The action of the acid is to bite away the steel between each tooth, both down-
wards and sideways, and the process being continued sufficiently long the natural
under cutting action of the acid will eventually throw off the flat tops of the old
teeth leaving the newly formed teeth extremely sharp.
In case the teeth of the file are not worn down equally, some being worn down
more than others, those teeth which have not been worn off may be brought down
to the level of the others by grinding, so that the tops of the new teeth will be all
the same height.
If the file is not satisfactory after the first series of operations the process may
be repeated until satisfactory results are obtained.
The improvements and advantages claimed for this my invention are these:-
That by protecting the worn part of the teeth from the action of the acid by the
use of a resistant varnish or some other suitable substance, I cause the acid to
remove only such parts of each tooth as are required to be removed in order to
make the tooth the same shape and sharpness as when new, and by first making the
tops of the old teeth level, I get the cutting edges of the new teeth all the same
height, and my invention applies equally well to all kinds of files, irrespective of
shape, size, or degree of cut.
Dated this 14th day of October 1893.
COMPLETE SPECIFICATION.
A Method of Sharpening Worn-out Files.
I, JAMES ELIJAH BRINDLEY late of Chesterton, and now of No. 13, Smith
Street Hanley in the County of Stafford, Engraver, do hereby declare the nature
of this invention and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement :-
This invention appertains to a method of treating worn-out files in such a manner
as to restore the teeth to their original shape and cutting edge and the details of
the process by which I do this are as follows.
It will be observed that the teeth of a file after being in use have lost their
original shape, the points of the teeth are worn away and become flat-topped.

page_text: Having first thoroughly cleansed the files I deposit on the worn or flat tops of
the teeth a coating of varnish or other substance which has the property of resisting
the corrosive action of acids.
I find ordinary Brunswick black to answer perfectly for this purpose, and it is
best applied by a small roller or dabber, taking care to avoid getting the varnish
into the furrows or channels between the teeth as that would prevent proper and
equal corrosion.
I then immerse the file in a liquid which will corrode or bite away the steel from
those parts (viz.: the bottom and sides of the furrows or grooves between the teeth)
which are not protected by the Brunswick black or other substance used, and the
best fluid for this purpose is a mixture of nitric acid and water, the proportions
varying according to the degree of fineness or "cut" of the file, but generally a
mixture of one part of strong nitric acid to nine parts of water will give the best
results.
The action of the acid is to bite away the steel between each tooth both down-
wards and sideways and the process being continued sufficiently long the natural
under cutting action of the acid will eventually throw off the flat tops of the old
teeth, leaving the newly formed teeth extremely sharp.
In case the teeth of the file are not worn-down equally, some being worn down
more than others, those teeth which have not been worn off may be brought down
to the level of the others by grinding, so that the new teeth will be all the same
height.
If the file is not satisfactory after the first series of operations, the process may be
repeated until satisfactory results are obtained.
Having now particularly described and ascertained the nature of my said inven-
tion, and in what manner the same is to be performed, I declare that what
I claim is,
That by the use of a resistant varnish applied to the worn teeth of a file, I cause
the acid to remove only such parts of each tooth as are required to be removed in
order to make the tooth the same shape and sharpness as when new, and by first
making the tops of the old teeth level, I get the cutting edges of the new teeth all
the same height, and my invention applies equally well to all kinds of files,
irrespective of shape, size, or degree of cut.
Dated this 11th day of July 1894.