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Repairing
Your Own Machine Components |
by:
Thomas
Yoon |
Many
industrial concerns have workshops of their
own. For the repair of worn shafts, the
lathe machine is excellent. Keyway slots
can be machined by using a milling machine,
while a shaping machine can do machining
of large flat areas. A drilling machine
does drilling of holes.
A skilled Maintenance Engineer should know
how to use all these machines in order to
make his own repairs in a safe manner. Very
often he has to supervise machinists. The
information below should be useful for that
purpose.
Lathe Machine
The lathe machine uses a single-point-cutting
tool for a variety of turning, facing, and
drilling jobs. Excess metal is removed by
rotating the work piece over the fixed cutting
tool to form straight or tapered cylindrical
shapes, grooves, shoulders and screw threads.
It can also be used for facing flat surfaces
on the ends of cylindrical parts.
The work piece is clamped onto a horizontal
rotating shaft by a 3-jaw or 4-jaw chuck.
The latter chuck can be used to cut off-centered
cylinders. The rotating horizontal spindle
to which the chuck is attached is usually
driven at speeds that can be varied.
The cutting tool is fixed onto a tool rest
and manipulated by hand. It can also be
power driven on straight paths parallel
or perpendicular to the work axis. This
is useful for screw cutting.
Internal turning known as boring results
in the enlargement of an already existing
hole. The holes are more accurate in roundness,
concentricity, and parallelism than drilled
holes. A hole is bored with a single-point-cutting
tool that feeds along the inside of the
work piece.
Shaping Machine
The shaping machine is used to machine flat
surfaces, grooves, shoulders, T-slots, and
angular surfaces with single-point tools.
The cutting tool on the shaper oscillates,
cutting on the forward stroke, with the
work piece feeding automatically toward
the tool during each return stroke.
Drilling Machine
The drilling machine is used to cut holes
in metal with a twist drill. By changing
the cutting tool, they can be used to do
reaming, boring, counter boring, countersinking,
and threading.
Milling Machine
The milling machine uses a rotating cutting
tool to cut flat surfaces, grooves, and
shoulders, inclined surfaces, dovetails,
and T-slots. Cutters of many shapes are
changed to cut different grooves.
Cutting Tools
Metal-cutting tools are classified as single
point or multiple point. The lathe and shaping
machine use single point cutting tool while
the milling and drilling machines use multiple-point-cutting
tools.
Metal is cut either by moving the work piece
like in the lathe or by moving the tool
like in the shaping machine, drilling or
milling machine. Clearance angles must be
provided to prevent the tool surface below
the cutting edge from rubbing against the
work piece. Rake angles are often provided
on cutting tools to cause a wedging action
in the formation of chips and to reduce
friction and heat.
Tool Materials
In order to remove chips from a work piece,
a cutting tool must be harder than the work
piece and must maintain a cutting edge at
the temperature produced by the friction
of the cutting action.
Carbon Steel
Carbon steel tools even though comparatively
inexpensive tend to lose cutting ability
at temperatures around 400 degree F (205
degree C).
High-Speed Steel
High-speed steel, containing 18 percent
tungsten, 4 percent chromium, 1 percent
vanadium, and only 0.5 to 0.8 percent carbon,
permits the operation of tools twice or
three times the speeds allowable with carbon
steel
Cast Alloys
Cast-alloy cutting-tool materials containing
cobalt, chromium, and tungsten are effective
in cutting cast iron and retaining their
cutting ability even when red hot.
Cemented Tungsten Carbide
The hardness of Tungsten Carbide approaches
that of a diamond. Tungsten carbide tools
can be operated at cutting speeds many times
higher than those used with high-speed steel.
Oxides
Ceramic, or oxide, tool tips consist primarily
of fine aluminum oxide grains, which are
bonded together. These are very hard.
Cutting fluids
An overheated tool can become blunt and
soft very fast. Therefore very often, cooling
fluids cools the cutting points of the tool.
This serves to lubricate and cool.
Water is an excellent cooling medium, but
it corrodes ferrous materials. Sulfurized
mineral oil is one of the most popular coolants
as it can both cool as well as lubricate.
The sulfur prevents chips from the work
from melting on to the tip of the tool.
About the author:
Many years of working experience in Marine,
Facilities, Construction has given the author
material for writing e-books and articles
related to engineering, and management.
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