ON THE USE OF THE FILE
The most necessary tool in a machine shop is a file. It is one of the
neglected tools, because the ordinary boy, or workman, sees nothing in
it but a strip or a bar with a lot of cross grooves and edges, and he
concludes that the only thing necessary is to rub it across a piece of
metal until he has worn it down sufficiently for the purpose.
THE FIRST TEST.--The fact is, the file is so familiar a tool, that it
breeds contempt, like many other things closely associated in life.
Give the boy an irregular block of metal, and tell him to file it up
square, and he will begin to realize that there is something in the
handling of a file that never before occurred to him.
He will find three things to astonish him:
First: That of dimensions.
Second: The difficulty of getting it square.
Third: The character of the surface when he has finished it.
FILING AN IRREGULAR BLOCK.--To file a block of an irregular character so
that the dimensions are accurate, is a good test for an accomplished
workman. The job is made doubly difficult if he is required to file it
square at the same time. It will be found, invariably, that the sides
will not be parallel, and by the time it is fully trued up the piece
will be too small. See Figs. 44 and 45.
Then, unless the utmost care is taken, the flat sides _will not_ be
flat, but rounded.
FILING A BAR STRAIGHT.--The next test is to get the boy to file a bar
straight. He has no shaper or planer for the purpose, so that it must be
done by hand. He will find himself lacking in two things: The edge of
the bar will not be straight; nor will it be square with the side of the
bar.
[Illustration: _Fig. 44. Rounded Surface_ _Fig. 45. A Winding Face_]
FILING BAR WITH PARALLEL SIDES.--Follow up this test by requiring him to
file up a bar, first, with two exactly parallel sides, and absolutely
straight, so it will pass smoothly between the legs of a pair of
calipers, and then file the two other sides in like manner.
SURFACING OFF DISKS.--When the foregoing are completed there is still
another requirement which, though it appears simple, is the supreme
test. Set him to work at surfacing off a pair of disks or plates, say
one and a half inches in diameter, so that when they are finished they
will fit against each other perfectly flat.
A pair of such disks, if absolutely true, will hold together by the
force of cohesion, even in a dry state, or they will, as it were, float
against each other.
TRUE SURFACING.--Prior to about 1850 the necessity of true surfacing was
not so important or as well known as at the present time. About that
period Sir J. Whitworth, an eminent English engineer and mechanic,
called the attention of machinists to the great advantage arising from
true surfaces and edges for all types of machinery, and he laid the
foundation of the knowledge in accurating surfacing.
PRECISION TOOLS.--Due to his energy many precision tools were made, all
tending to this end, and as a result machines became better and more
efficient in every way.
It had this great advantage: It taught the workman of his day how to use
the file and scraper, because both must be used conjunctively to make an
absolutely flat plate.
Contrary to general beliefs, shapers and planers do not make absolutely
accurate surfaces. The test of this is to put together two plates so
planed off. There is just enough unevenness to permit air to get between
the plates. If they were perfectly true they would exclude all air, and
it would be a difficult matter to draw them apart.
TEST OF THE MECHANIC.--To make them perfectly flat, one plate has chalk
rubbed over it, and the two plates are then rubbed together. This will
quickly show where the high spots are, and the file and scraper are then
used to cut away the metal.
[Illustration: _Fig. 46. Fig. 47. Hexagon Nut_]
In England the test of the mechanic used to be determined by his ability
to file a piece of metal flat. It was regarded as the highest art. This
is not the most desirable test at the present time, and it is recognized
that a much severer test is to file a narrow piece exactly flat, and so
that it will not have a trace of roundness, and be square from end to
end.
TEST SUGGESTIONS.--In a shop which does not have the advantage of a
planer or shaper, there are so many articles which must be filed up,
that it is interesting to know something of how the various articles are
made with a file.
To file a hexagon, or six-sided nut will be a good test with a file. To
do this a little study in geometrical lines will save a vast amount of
time. In beginning the work, measure the radius with a divider, and then
step off and make six marks equidistant from each other on the round
surface.
[Illustration: _Fig. 48. Cutting Key-way_]
USE OF THE DIVIDERS.--The distance between each of these points is equal
to the radius, or half the diameter, of the round bar. See Fig. 46,
which shows this. The marks should be scribed across the surface, as
shown in Fig. 47, where the lines show the ends of the facets of the
outside of the nut.
Do not let the file obliterate the lines at the rough cutting, but
leave enough material so you can make a good finish at the line.
CUTTING A KEY-WAY.--Another job you may have frequent occasion to
perform, is to cut a way for a key in a shaft and in a wheel hub.
Naturally, this will be first roughed out with a cold chisel narrower
than the key is to be, and also slightly shallower than the dimensions
of the key.
A flat file should be used for the purpose, first a heavy rough one, for
the first cutting. The better way is to have the key so it can be
frequently tried while the filing process is going on, so that to fit
the key in this way is a comparatively easy task.
KEY-WAY DIFFICULTIES.--But the trouble commences when the groove is
filed for the depth. Invariably, the mistake will be made of filing the
width first, so the key will fit in. As a result, in deepening the
groove the file will contact with the walls, and you have a key-way too
wide for the key.
To avoid this, file the depth, or nearly so, and then with a fine file
cut in the corners in the direction indicated by the dart, Fig. 48.
A proper key is square in cross section. In such a case the depth of the
key-way, at each side wall, is just half the width of the key-way.
An excellent key-seat rule can be made by filing out two right-angled
pieces, as shown in Fig. 49, which can be attached to the ordinary
six-inch metal rule, and this will enable you to scribe the line
accurately for the key-way on the shaft.
[Illustration: _Fig. 49. Key-seat Rule_]
[Illustration: _Fig. 50. Fig. 51. Filing Metal Round_]
FILING METAL ROUND.--It is sometimes necessary to file a piece of metal
round. This is a hard job, particularly where it is impossible to scribe
the end of the piece. Suppose it is necessary to file up a bearing
surface, or surfaces, intermediate the ends of a square bar.
You have in that case four sides to start from, the opposite sides
being parallel with each other, so that you will have two dimensions,
and four equal sides, as shown in Fig. 50.
The first step will be to file off accurately the four corners 1, 2, 3,
4, so as to form eight equal sides or faces, as shown in Fig. 51. If you
will now proceed to file down carefully the eight corners, so as to make
sixteen sides, as in Fig. 52, the fourth set of corners filed down will
make the filed part look like the illustration Fig. 53 with thirty-two
faces.
[Illustration: _Fig. 52. Fig. 53. Making a Bar Round_]
This may be further filed down into sixty-four faces, and a few cuts of
the finishing file will take off the little ridges which still remain.
By using emery cloth, and wrapping it around the bearing portion, and
changing it continually, while drawing it back and forth, will enable
you to make a bearing which, by care, will caliper up in good shape.
KINDS OF FILES.--Each file has five distinct properties; namely: the
length, the contour, the form in cross section, the kind of teeth, and
the fineness of the teeth.
There are nine well-defined shapes for files. These may be enumerated as
follows:
[Illustration: _Fig. 54. Cross Sections of Files._]
No. 1. The cotter file. The small kind is called a verge or pivot file.
No. 2. Square file, which may be tapering from end to end, or have
parallel sides throughout.
No. 3. Watch pinion file. This may have its sides parallel or tapering,
to make a knife-shaped file.
No. 4. Clock-pinion; which may be used for either nicking, piecing, or
squaring-off purposes.
No. 5. Round, with parallel sides for gulleting purposes, or rat-tail
when it tapers.
No. 6. Triangular, or three equally-sided body for saw filing.
No. 7. Equalizing file. This is parallel when used for making
clock-pinions or endless screws; or for slitting, entering, warding, or
making barrel holes, when the body of the file tapers.
No. 8. Cross, or double-round, half-file.
No. 9. Slitting file; which has parallel sides only. A cant file.
CHARACTER OF THE FILE TOOTH.--Files are distinguished principally by the
character of the oblique, or cross grooves and ridges which do the
cutting and abrading when the file is drawn across the surface.
This is really more important than the shape, because the files, by
their cuttings, are adapted for the various materials which they are to
be used upon.
The files are classified as _Double Cut_, of which there are the
_rough_, _middle_, _bastard_, _second cut_, _smooth_, and _dead smooth_.
The _Float Cut_, which is either _rough_, _bastard_ or _smooth_; and
The _Rasp Cut_, either _rough_, _bastard_ or _smooth_.
Several types are illustrated in Fig. 55, which show the characteristics
of the various cuts.
The rasps are used principally for soft material, such as wood or for
hoofs, in horse shoeing, hence they need not be considered in connection
with machine-shop work.
[Illustration: _Fig. 55. Files._]
HOLDING THE FILE.--The common mistake on the part of the beginner is to
drag the file across the work at an angle. The body of the file should
move across straight and not obliquely.
Note this movement in Fig. 56 where the dash shows the correct movement
of the file with relation to the work. Also observe that the file
cutting ridges are not straight across the file, but at an angle to the
direction of the dart.
[Illustration: _Fig. 56. Correct File Movement_]
INJURING FILES.--Now the frequent practice is to use the file as shown
in Fig. 57, in which case it is moved across obliquely. The result is
that the angle of the file cut is so disposed that the teeth of the file
do not properly aid in the cutting, but in a measure retard the
operation.
File teeth are disposed at an angle for the purpose of giving them a
shearing cut, which is the case when the file moves across the work on a
line with its body.
To use a file as shown in Fig. 57 injures the file without giving it an
opportunity to cut as fast as it would when properly used.
[Illustration: _Fig. 57. Incorrect File Movement_]
DRAWING BACK THE FILE.--In drawing back a file it is always better to
allow it to drag over the work than to raise it up. It is frequently the
case that some of the material will lodge in the teeth, and the back
lash will serve to clear out the grooves.
This is particularly true in filing copper, aluminum, lead, and like
metals, but it is well to observe this in all cases.