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Figure 1-22.—Polishing operations | Up
Aviation Boatswains Mate E - Aviation theories and other practices | Next
Figure 1-24.—Twist drill nomenclature. |
If your cloth is in a roll and if the job you are
polishing is the size that would be held in a vise, tear off
a 6- or 8-inch length of the 1- or 2-inch width. If you are
using sheets of abrasive cloth, tear off a strip from the
long edge of the 8- by 11-inch sheet.
Wrap the cloth around the file (fig. 1-22, view A)
and hold the file as you would for drawfiling. Hold the
end of the cloth in place with your thumb. In polishing,
apply a thin film of lubricating oil on the surface being
polished and use a double stroke with pressure on both
the forward and the backward strokes. Note that this is
different from the drawfiling stroke in which you cut
with the file in only one direction.
When further polishing does not appear to improve
the surface, you are ready to use the next finer grade of
cloth. Before changing to the finer grade, however,
reverse the cloth so that its back is toward the surface
being polished.
Work the reversed cloth back and forth in the
abrasive-laden oil as an intermediate step between
grades of abrasive cloth. Then, with the solvent
available in your ship, clean the job thoroughly before
proceeding with the next finer grade of cloth. Careful
cleaning between grades helps to ensure freedom from
scratches.
For the final polish, use a strip of crocus
cloth—first the face and then the back—with plenty of
oil. When polishing is complete, again carefully clean
the job with a solvent and protect it with oil or other
means, from rusting.
In figure 1-22, A of view B shows another way to
polish, in which the abrasive cloth is wrapped around a
block of wood. In B of view B, the cloth has simply
been folded to form a pad, from which a worn, dull
surface can be removed by simply tearing it off to
expose a new surface.
POLISHING ROUND-METAL STOCK.—In
figure 1-22, view C, a piece of round stock is being
polished with a strip of abrasive cloth, which is
"seesawed" back and forth as it is guided over the
surface being polished.
Remember that the selection of grades of abrasive
cloth, the application of oil, and the cleaning between
grades applies to polishing, regardless of how the cloth
is held or used.
Care of Files
A new file should be broken in carefully by using it
first on brass, bronze, or smooth cast iron. Just a few of
the teeth will cut at first, so use a light pressure to
prevent tooth breakage. Do not break in a new file by
using it first on a narrow surface.
Protect the file teeth by hanging your files in a rack
when they are not in use or by placing them in drawers
with wooden partitions. Your files should not be
allowed to rust—keep them away from water and
moisture. Avoid getting the files oily. Oil causes a file to
slide across the work and prevents fast, clean cutting.
Files that you keep in your toolbox should be wrapped
in paper or cloth to protect their teeth and prevent
damage to other tools.
Never use a file for prying or pounding. The tang is
soft and bends easily. The body is hard and extremely
brittle. Even a slight bend or a fall to the deck may
cause a file to snap in two. Do not strike a file against
the bench or vise to clean it—use a file card.
Safety
Never use a file unless it is equipped with a
tight-fitting handle. If you use a file without the handle
and it bumps something or jams to a sudden stop, the
tang may be driven into your hand. To put a handle on a
file tang, drill a hole in the handle, slightly smaller than
the tang. Insert the tang end, and then tap the end of the
handle to seat it firmly. Make sure you get the handle on
straight.
TWIST DRILLS
Making a hole in a piece of metal is generally a
simple operation, but in most cases an important,
precise job. A large number of different tools and
machines have been designed so that holes may be
made speedily, economically, and accurately in all
kinds of material.
To be able to use these tools efficiently, it is
important that you become acquainted with them. The
most common tool for making holes in metal is the
twist drill. It consists of a cylindrical piece of steel with
spiral grooves. One end of the cylinder is pointed, while
the other end is shaped so that it may be attached to a
drilling machine. The grooves, usually called FLUTES,
may be cut into the steel cylinder, or the flutes may be
formed by twisting a flat piece of steel into a cylindrical
shape.
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