7.
2 Workshop
Practices
Care of Tools - Control of Tools - Use of Workshop
Materials - Tool Calibration - Standards of
Workmanship - Dimensions, Allowances, Tolerances
Workshop Practices
Despite the enormous advances in the mechanisation and computerisation of
the engineering industry in general, there remains the requirement for a high
degree of hand skills on the part of technicians who are engaged in the
day-to-day maintenance of aircraft and their associated components.
It is necessary to remove many items of equipment for cleaning, inspection,
overhaul and, if needed, repair before they are, subsequently, re-installed in
their appointed locations.
Care of Tools
Engineers are responsible for the maintenance of their personal tools,
the responsibility of engineers to ensure that any tools, or other items of equipment
they use, are not left in an aircraft or associated components.
The care required for different tools can vary.
Ordinary hand tools may merely require racking or locating within sturdy tool
boxes, with careful visual check daily.
Precision instruments be kept in special, soft-lined, boxes within other storage
facilities.
Prior to use they should have a zero check or calibration.
Some tools require that they have a light coating of machine oil, to prevent the onset
of corrosion
Control of Tools
Control of tools is important to good engineering practices and is also
vital to flight safety
One form of control is the shadow board and tool tag system.
Special Tools - Ex. Wheel bay special tools
No matter where tools are being used, it is the responsibility of each
technician to keep track of ALL of the tools used during a particular task.
End of Work tool check - all tools collected and checked off, borrowed
tools returned, personal tags collected back.
Use of Workshop Materials
Many of the wide variety of materials, used in workshops, require some form
of control in their handling. This control can involve
Safety: relating to such topics as the toxicity, corrosiveness or other
health risks associated with the use of certain materials
Management: referring to the storage, use and correct handling of all
materials whether they are solid, liquid, or, in some instances, gaseous
Economy: involving such matters as to the using of the correct dosage or
proportions when mixing compounds, using only as much material as
required for a specific task and to the keeping in stock of only sufficient
materials and thus avoiding lifed items reaching their expiry dates
before being used.
Tool Calibration
This topic provides an overall picture of the types of requirements and tests required in
establishing and maintaining an effective calibration system. It takes into account factors
such as the degree of accuracy required, frequency of use and the reliability of the
equipment.
The key factor is the need to establish confidence in the accuracy of the equipment when it
is required for use.
standards used are attributed upon
The standard specified by the equipment manufacturer/design organisation (or)
The appropriate National/International Standards.
Tool Calibration
PROCEDURES
A clear system of labelling calibrated appliances is necessary setting out when
the next inspection, service or calibration is due and indicating the
serviceability.
Some tools require calibration on a regular basis, and some every time before
use. Ex. Micrometer, Torque wrench, tyre pressure gauges
Tool Calibration
PROCEDURES
Calibration records or certificates should as a minimum, 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
Tool Calibration
CALIBRATION STANDARDS
The standard specified by the appliance manufacturer/design
organisation
The appropriate national/international standard
National Accreditation of Measurement and Sampling. (NAMAS)
United Kingdom Accreditation
Standards of Workmanship
A Standard is an agreed way of doing something. It can be recorded and
published formally, or may simply be a company's informal unwritten
procedure.
Standards are vital tools of industry and trade because they promote
understanding between buyers and sellers.
International Standards provide a reference framework, or a common
technological language, between suppliers and their customers - which
facilitates trade and the transfer of technology.
Standards of Workmanship
For businesses, the widespread adoption of International Standards means
that suppliers can base the development of their products and services on
specifications that have wide acceptance in their sectors.
For customers, International Standards brings them an increasingly wide
choice of offers, and they also benefit from the effects of competition among
suppliers.
For governments, International Standards provide the technological and
scientific bases underpinning health, safety and environmental legislation.
For developing countries, International Standards give developing countries
a basis for making the right decisions when investing their scarce resources
and thus avoid squandering
Standards of Workmanship
For consumers, conformity of products and services to International
Standards provides assurance about their quality, safety and reliability.
For everyone, International Standards can contribute to the quality of life in
general by ensuring that the transport, machinery and tools we use are safe.
For the planet we inhabit, International Standards on air, water and soil
quality, and on emissions of gases and radiation, can contribute to efforts to
preserve the environment
Standards of Workmanship
Standards may be one of the following types:
1. Private Standards
2. Open source Standards. Ex- MS Windows, Linux
3. Formal Standards
4. National Standards, e.g. British Standards (suffix BS), BIS (ISI), ANSI
5. Publicly Available Standards (PAS)
6. European Standards (suffix EN)
7. International Standards (suffix ISO)
8. International Electro-technical Standards (suffix IEC)
Dimension, Tolerances and Allowances
Associated Terms:
Feature: Physically identifiable portion of a part, such as a hole, slot, pin, or chamfer.
Nominal Size: An approximate dimension that is used for the purpose of general
identification.
Basic Size: The theoretical size from which limits of size are derived by applying
allowances and tolerances.
Actual size: The measured size of a finished part.
Dimension, Tolerances and Allowances
Tolerance: The total amount by which a given dimension is allowed to vary.
Limit dimensions: The maximum and minimum dimensions of a machined part.
Bilateral Tolerance: Deviation (plus or minus) from the basic size.
Unilateral Tolerance: Deviation in one direction only from the basic size.
Clearance: The space between mating parts
Interference: Negative clearance.
Dimension, Tolerances and Allowances
Maximum Material Condition: The condition where a feature of a certain size contains
the maximum amount of material within the stated limits of that size.
Allowance: The minimum clearance space (or maximum interference) intended
between the maximum material condition of mating parts.
allowance = smallest hole largest shaft.
Dimension, Tolerances and Allowances
Fit: The looseness or tightness that can result from the application of a specific
combination of allowance and tolerance in the design of mating part features.
Clearance Fit: Fit that allows for sliding or rotation between mating parts.
Interference Fit: A force or shrink fit which results in surface contact and surface forces
due to the overlap of physical material for the entire range of tolerances between mating
parts.
Dimension, Tolerances and Allowances
Transition Fit: A fit between mating parts which may be a clearance or interference fit
used for accurate location of parts.
Geometric Tolerancing: Tolerances that involve shape features of the part.
Datum: A theoretically exact axis, point, line, or plane.
