UNIT: Maintenance Practice Tool

Care of Tools
• Each engineer is responsible for the acquisition and maintenance of
his or her own common hand tool set. Wrenches, spanners, socket
sets, hammers, screwdrivers, pliers.
• Tools must be kept clean. A light coating of oil wiped on the tool
after use helps prevent corrosion of steel tools.
• Complicated or precision tools should be inspected, zeroed or
calibrated, and operated.
• If ever in doubt about how to use a tool, the technician should seek
assistance from an experienced colleague or the manufacturer of
the tool.
 CONTROL OF TOOLS

• Most important responsibilities of the engineer is the control of

tools. A misplaced tool can have catastrophic effects resulting in
significant expense and the possible loss of life.
• Organizing one's tool storage so that all tools can be accounted for
is a good practice.
• In other words, tool box tool storage should be executed in such a
way that every tool is kept in a specific place and the engineer can
quickly see when a tool is missing.
• The tools are frequently labeled with an identification number or
have a bar code label attached directly to the tool for identification.
 USE OF WORKSHOP MATERIALS
• Toxic materials may cause health risks which can be controlled by
controlling the handling and storage of this type of substance.
• Abrasive papers, solder and brazing materials, wire wool, tire
• powder, oil spill powder and so on, all require control of issue and use,
though they may not, normally, require stringent safety precautions.
• These include oils, greases, some adhesives, sealing and glazing
compounds in addition to many paints, enamels and epoxy
surface :finishes. When stored, the materials and storage cabinets are kept
out of direct sunlight in a workshop or hangar.
• When handling materials that give off fumes, it is necessary to have the
area well ventilated and/or have the operator wearing a mask or some
form of remote breathing apparatus.
• All liquids must only be used for the purpose for which they are designed
and never mixed together, unless the two materials are designed to be
mixed, such as with two part epoxy adhesives and sealants.
• Liquids must never be disposed of by pouring them into spare or
unidentified containers and they must not be allowed to enter the
'domestic' drains systems.
• Another area of hazardous workshop materials is that of gases
stored in high pressure containers such as nitrogen and oxygen.
 TOOL CALIBRATION
• Large companies keep inventory control over tools that need
periodic calibration and may have a calibration shop in-house. They
may also send tools out to independent agencies that perform the
calibration.
• An engineer who owns a tool that requires periodic calibration must
ensure that it is performed or the tool is not suitable for use in
maintenance work on an aircraft.
• Annual calibration is common on tools that hold calibration well.
Sensitive instruments, especially electrical instruments, are
calibrated by the user before each use. They may also require
periodic calibration.
• The calibration of test equipment is best achieved by the operation
of a methodical system of control.
• A written record is kept for all tools the require calibration, detailing
when last done, when next due, and the requirements of the
calibration. A sticker is attached to the tool detailing the due date of
the next calibration.
• Calibration records or certificates should contain the
following information:
• Identification of equipment
• Standard used
• Results obtained
• Uncertainty of measurement
• Assigned calibration interval
• Limits of permissible error
• The authority under which the release document was issued
• Any limitation in the use of the equipment
• Date on which each calibration was conducted
 DIMENSIONS, ALLOWANCES, TOLERANCES
• The aircraft maintenance engineer works with consideration for
dimensions, allowances and tolerances.
• A dimension is a measurable extent of some kind, such as length, width, or
height. Aircraft components including hardware have dimensions that
physically describe the item from a size prospective.
• A limit dimension is the maximum or minimum dimension of a machined
part.
• When referring to the size of an item, nominal size is an approximate
dimension that is used for the purpose of general identification.
• The basic size is the theoretical size from which limits of size are derived
by applying allowances and tolerances. The actual size of a part is the
measured size. A tolerance is the total amount by which a given dimension
is alloyed to vary. Thus, if a basic size is known and the tolerance is known,
one can measure the actual size of a part and know whether it is within
tolerance.
• For Example, the diameter of a piston is 4.0 inches. This is its basic size.
The tolerance established by the engine manufacturer is .005 inch. This
means that if the piston is measured, its actual size must be between
3.995 inches and 4.005 inches to be within tolerance. If it is not, the piston
is rejected for use in the engine.
• Any measurement of the piston that is greater than the basic size would
be cause for rejection because there is no tolerance in that direction.
• Tolerance can be used when examining the dimension of a single part or it
can be used when comparing the dimensional relationship between two
parts, which is known as fit.
• When examining fit, clearance is the space between mating parts.
• There are different types of fits which reflect variations in the clearance
between parts. Generally, one can refer to a loose fit or a tight fit, etc.
• A clearance fit is a fit that allows for sliding or rotating between mating
parts. An interference fit is one in which the dimensions of two parts over
lap - such as when a pin diameter is slightly larger than the hole in which it
is to be inserted.
• An allowance is the minimum clearance space intended between two
parts.
• A limit is the maximum or minimum dimension formed when maximum or
minimum tolerance is considered.
• Maintenance instructions typically specify measurable values and
tolerances for acceptable actions. Maintenance actions that do not
achieve these values within tolerances cause the aircraft to remain
unairworthy and it must not be released for service.
 TOOLS
• The most common hand tools and measuring instruments used in aircraft
repair work.
• The use of tools may vary, but good practices for safety, care, and storage
of tools remain the same.
• Layout and measuring devices are precision tools. They are carefully
machined, accurately marked and, in many cases, are made up of delicate
parts.
• The inch may be divided into smaller parts by means of either common or
decimal fraction divisions.
• RULER:
• Rules (also called rulers or line gauges) are made of steel and are either
rigid or flexible.
• The inch may be divided into smaller parts by means of either common or
decimal fraction divisions.
• COMBINATION SETS:
• CALIPERS:

Outside calipers are

used for measuring
outside
dimensions - for
example, the diameter
of a piece of
round stock. Inside
calipers have outward
curved legs
for measuring inside
diameters, such as
diameters of
holes, the distance
between two surfaces,
the width of
slots, and other similar
jobs.
• MICROMETER CALIPERS:
• There are four types of micrometer calipers, each designed for a specific
use: outside micrometer, inside micrometer, depth micrometer, and
thread micrometer.
• It may be used to measure the outside dimensions of shafts, thickness of
sheet metal stock, the diameter of drills, and for many other applications.
• Vernier Scale:
• A vernier calliper is defined as a measuring device that is used for the
measurement of linear dimensions. It is also used for the measurement of
diameters of round objects with the help of the measuring jaws.
• DIAL INDICATOR:
• A variation of the micrometer is the dial indicator, which measures
variations in a surface by using an accurately machined probe
mechanically linked to a circular hand whose movement indicates
thousandths of an inch, or is displayed on a liquid crystal display (LCD)
screen.
 GENERAL PURPOSE TOOLS

• SCREWDRIVERS
• PLIERS AND PLIER-TYPE CUTTING TOOLS
• CLAMPS AND VISES
• HAMMERS AND MALLETS
• PUNCHES
• Punches are used to locate centers for drawing circles, to start holes for
drilling, to punch holes in sheet metal, to transfer location of holes in
patterns, and to remove damaged rivets, pins or bolts.
• WRENCHES
• The wrenches most often used in aircraft maintenance are classified as
open-end, box-end, socket, adjustable, ratcheting and special wrenches.