Unit 3 Prepare and Interpret Technical Drawing
Unit 3 Prepare and Interpret Technical Drawing
Unit 3 Prepare and Interpret Technical Drawing
UNIT DESCRIPTOR : This unit covers the knowledge, skills and attitudes and values needed to
prepare/interpret diagrams, engineering abbreviation and drawings, symbols, dimension.
Learning outcomes
Layout drawing
A general arrangement (GA) drawing depicts the physical relationship of significant items using
appropriate projections or perspective views.
Reference dimensions are to be included in GA drawing.
The GA drawing does not establish item identification.
It is prepared to convey a general description of the configuration and location of significant
items.
The GA drawing normally includes (i) sufficient views so that a general understanding of the
configuration and location of significant items is conveyed, (ii) overall, locating, and other
general dimensions necessary to describe the configuration, (iii) identities of significant items,
and (iv) reference to applicable documents for further details.
Detail drawing
A detail drawing provides the complete end-product definition of the part or parts depicted on
the drawing.
A detail drawing establishes item identification for each part depicted thereon.
It is either a mono detail drawing or a multi detail drawing.
A mono detail drawing defines a single part.
It is prepared to provide maximum clarity in defining the part.
It describes all features of the part which include configuration, dimensions, tolerances,
materials, mandatory processes, surface texture, protective finishes and coatings, and markings.
A multi detail drawing defines two or more uniquely identified parts in separate views or in
separate sets of views on the same drawing.
It is a single drawing prepared to describe parts usually related to one another. A multi detail
drawing is to be used cautiously.
The same revision status applies to all details on a multi detail drawing and hence a change to
one detail of the drawing can affect the associated records of all other details (material control
data, manufacturing planning, and microfilm etc.).
Some significant benefits are to outweigh this potential disadvantage, as well as such others as
diminished clarity and usefulness resulting from increased drawing complexity.
Assembly drawing
Assembly
drawing defines the configuration and contents of the assembly or assemblies depicted
thereon.
It establishes item identification for each assembly.
Where an assembly drawing contains detailed requirements for one or more parts used
in the assembly, it is a detail assembly drawing.
The assembly drawing is prepared for each group of items which are to be joined to
form an assembly and that reflect one or more of the (i) a logical level in the assembly
or disassembly sequence, (ii) a testable item, (ii) a functional item and (iv) a deliverable
item.
It is the preferred drawing type for an inseparable assembly.
However, individual pieces of the inseparable assembly need not be individually detailed
provided they are controlled by the specified assembly requirements or by separate
detail drawings.
Attached parts (bolts, nuts, and washers etc.) required to mount assemblies in next higher assemblies or
on foundations are included in the parts list of the drawing which defines the attachment (usually the
higher level assembly or installation drawing). Assembly drawings may be tabulated by specifying
variable items in the parts list.
Erection drawings
An erection drawing provides information for properly positioning and installing items relative
to their supporting structure and adjacent items.
This information includes dimensional data, hardware descriptions, and general configuration
information for the installation site.
The erection drawing is prepared to provide detailed installation information for (i) functionally
related items (such as a control system, electrical system, or hydraulic system) which cannot be
effectively shown on an assembly drawing of the item to which it belongs, or (ii) a part or
assembly which is so large or complex that the major assembly drawing cannot accommodate all
relevant data.
An erection drawing normally includes (i) overall and principal dimensions in sufficient detail to
establish space requirements for installation, operation, and servicing including clearances for
opening of doors, removal of plug-in units and travel or rotation of any moving parts (including
the centres of rotation, angles of elevation and depression), (ii) interface mounting and mating
information (e.g. locating dimensions for attaching hardware), (iii) interfaces for pipe and cable
attachments, (iv) information necessary for preparation of foundation plans including mounting
details, (v) references to interconnecting and cabling data and to associated lists, (vi)
identification of and requirements for installation items not included in the parts list of the using
assembly drawing, (vii) reference to the assembly drawing of the major item being installed,
(viii) a parts list specifying the items to be installed thus establishing item identification for a
work package, and (ix) supporting structure or associated items which are not included in the
installed items.
Control drawings
Control drawing is that drawing which is used for the control of certain activities.
There are usually six categories of control drawing (Fig 1) as given below.
The first category of control drawing is the procurement control drawing.
It provides criteria for performance, acceptance, and identification of supplier items by
disclosing the engineering design characteristics required normally for control of interfaces and
to ensure repeatability of performance.
It is prepared to specify criteria for (i) purchased items, (ii) alterations to purchased items, (iii)
selection from purchased items, (iv) development and qualification of new items, and (v) item
identification.
It includes (i) performance requirements to ensure that performance characteristics critical to
the intended application are met, (ii) envelope dimensions to ensure physical interchangeability
in using assemblies, (iii) interface characteristics to ensure functional interchangeability in using
assemblies, (iv) qualification requirements necessary to verify that performance requirements
and functional interchangeability, (v) identification requirements including marking, instructions,
lot serialization, etc., (vi) procurement data, (vii) acceptance criteria, and (viii) to identify any
variations between items.
The second category of control drawing is the vendor Item drawing.
It provides an engineering description and acceptance criteria for purchased items.
It provides sufficient engineering definition for acceptance of interchangeable items within
specified limits.
It is used to provide engineering requirements for a purchased item.
It is not the intent of a vendor item drawing to portray a complete design disclosure.
This drawing discloses sufficient information to ensure identification and re-procurement of
interchangeable items.
The drawing includes (i) configuration, (ii) dimensions of item envelope and their limits, (iii)
mounting and mating dimensions and their limits, (iv) interface characteristics and their limits,
(v) acceptance criteria, (vi) performance, maintainability, reliability, environmental, and other
functional characteristics, (vii) schematic, interconnection, or other appropriate diagram to
define item function or provide inter-connection information.
The third category of control drawing is the source control drawing.
It provides engineering description and acceptance criteria for purchased items which need
design activity imposed qualification testing and exclusively provide performance, installation,
and interchangeability characteristics specifically required for the critical applications. It
establishes item identification for the controlled items.
It is used to provide a means of establishing engineering requirements for the selection,
qualification testing, and acquisition of an item, and documentation to assure interchangeability
of specified items.
It includes (i) configuration, (ii) dimensions of item envelope and their limits, (iii) mounting and
mating dimensions and their limits, (iv) interface characteristics and their limits, (v) acceptance
criteria, (vi) qualification test requirements, (viii) performance, maintainability, reliability,
environmental, and other functional characteristics, (ix) schematic, interconnection, or other
appropriate diagram to define item function or provide interconnection information, and (x)
identification requirements including marking instructions.
The fourth category of control drawing is the design control drawing.
It discloses the basic technical information and performance requirements necessary for a
contractor to complete the detailed design required to develop and produce an item.
The drawing in itself does not provide complete design for which a detailed design drawing is
needed. It includes those details which are necessary to develop the detail design of the item
such as (i) configuration, mounting, mating, and other necessary dimensions, (ii) performance,
installation, reliability, and interchangeability requirements, (iii) test requirements,
(iv) schematic, connection, or other appropriate diagram (if electrical, electronic or other
circuitry is involved), (v) the mating connections, their location, and a connection diagram, and
(vi) reference to other documentation.
The fifth category of control drawing is the interface control drawing. It depicts physical and
functional interfaces of related or co-functioning items.
It does not establish item identification.
This drawing controls one or more of the interfaces such as mechanical, electrical,
interconnections, configuration, installation, operational sequence requirements, and system
switching etc.
The drawing includes (i) configuration and interface dimensional data applicable to the
envelope, mounting, and interconnection of the related items, (ii) complete interface
engineering requirements (mechanical, electrical, electronic, hydraulic, and pneumatic etc.)
which affect the physical or functional characteristics of the co-functioning items, and (iii) any
other characteristics which cannot be changed without affecting system interfaces.
The sixth category of control drawing is the identification cross reference drawing.
It is an administrative type drawing which assigns unique identifiers which are compatible with
automated data processing systems, item identification specifications, and provides a cross
reference to the original incompatible identifier.
It does not specify any engineering or design requirements beyond those already contained in
the drawings, and specification etc. governing the original item.
Fig 1 Categories of control drawing
Civil drawing
Civil drawing is used for specifying the shape and position of the civil foundation.
It typically includes the information such as (i) setting out dimensions for the concrete structure
on site, (ii) plans, sections and elevations showing layout, dimensions and levels of all concrete
members, (iii) location of all holes, chases, pockets, fixings and other items affecting the
concreting work, (iv) notes on specifications, finishes and all cross-references affecting the
construction.
The drawing provides the detailer with the layout and sectional information required to specify
the length, shape and number of each type of reinforcing bar.
Reinforcement drawing is part of civil drawing.
It fully describes and locates all reinforcements in relation to the finished surface of the concrete
and to any holes or fixings.
Structural drawing
A structural drawing is a type of technical drawing which depicts the design and working
drawings for building as well as technological structures.
It includes a plan or set of plans for the building or other structures.
Structural drawings are primarily concerned with the load-carrying members of a structure.
They outline the size and types of materials to be used, as well as the general demands for
connections. They do not address architectural details like surface finishes, partition walls, or
mechanical systems. The structural drawings guide in detailing, fabricating, and installing parts
of the structure.
Structural drawings are of three types namely (i) design drawings, (ii) detail fabricating drawings,
and (iii) erection drawings. Structural detail fabrication drawing includes all the details needed
for the fabrication of the structures.
Printed board drawing sets consist of those drawings which define the configuration of printed
wiring or printed circuit boards and assemblies.
They establish requirements for assembly and test.
A typical drawing set includes an assembly drawing, schematic diagram, master drawing, and
may include an artwork master.
It specifies the engineering requirements for assembly and includes (i) identification of parts,
materials, and processes required for the assembly, (ii) electrical insulating requirements, (iii)
reference designations, terminal identification, polarity symbols, and index marks, (iv) control
dimensions, (v) jumper wires, (vi) requirements for identification and traceability marking, spot
bonding, conformal coating, and masking, part mounting, support, and assembly, cleanliness,
part orientation and polarity, electrostatic discharge protection, special solder plug, lead
forming, and electric testing , (vii) solder mask, and (ix) reference document identification.
A master drawing provides the complete engineering description of a printed board which
includes (i) all dimensions and tolerances necessary to establish board size and shape, mounting
hole locations, cutouts, and hole sizes, etc., (ii) un-dimensioned holes located by the conductor
pattern and at theoretical grid intersections, (iii) minimum annular rings for conductor patterns
surrounding terminal holes to control both hole-to-terminal relationship and registration
between layers, (iv) minimum conductor width, spacings, and distance to board edges, (v)
registration marks to assure proper alignment of patterns and marking masters on two-sided
and multilayer boards, (vi) definition of the cross section details of multilayer boards, (vii)
dielectrics thickness between layers of multilayer boards, (viii) raw materials and plating
requirements, (ix) etch back allowances, (x) reference designation marking, (xi) maximum rated
voltage, (xi) identification and traceability marking requirements, (xii) test points, (xiii) test tab
requirements, (xiv) the shape and arrangement of conductor or circuit patterns, hole locations,
and printed marking requirements, (xv) critical pattern features which may affect circuit
performance, (xvi) views of conductor or circuit patterns and printed marking requirements,
(xvii) applicable process specification, and (xviii) process allowances used in preparing the
artwork master. Artwork master is a precision scale pattern on stable base material used to
produce printed boards within the accuracy established by the master drawings and to establish
and control the configuration of the conductor or circuit and marking patterns when these
details are not included in the master drawings.
A microcircuit drawing specifies the engineering requirements and establishes item
identification for a microcircuit.
It is prepared to establish the physical and functional characteristics necessary to ensure
microcircuit interchangeability.
It includes (i) outline and mounting requirements, (ii) performance requirements, (iii) schematic
diagrams showing functional electrical elements of the microcircuit, (iv) marking requirements,
(v) identification of input and output pin functions, and (vi) quality assurance provisions.
An un-dimensioned drawing represents the shape and other design features of an object at a
precise scale predominantly without dimensions.
It is prepared to describe items which can be fabricated by use of the patterns to produce the
item or to produce a tool for use in fabricating the item.
It includes (i) information necessary to manufacture the depicted items within required design
limits, (ii) an x-y coordinate grid or scale for dimensional verification of the drawing, and (iii)
tolerance dimensions where greater or lesser control is required for specific features.
A kit drawing identifies an item or group of items with instructions for their use. It does not
necessarily define a complete functional assembly.
It is prepared when it is desired to identify all of the items required to perform a specific
operation in kit form.
It includes (i) a parts list of the contents of the kit including the identification of each item, (ii)
documents which are a part of the kit, (iii) pictorial representations, (iv) special tool
requirements for installation of the kit, and (v) retest or recalibration requirements.
A pipe bend drawing establishes, by pictorial or tabular description or a combination thereof,
end product definition for a single, multi-plane, pipe or pipe assembly along with the
identification for the bent pipe or pipe assembly.
It is prepared to specify complete requirements and configuration of rigid or semi-rigid piping
for direct use in forming on a draw bending machine.
It is prepared as a detail, assembly, or detail assembly drawing. It includes (i) pipe material, (ii)
end types, (iii) identification and quantity of fittings, (iv) dimensional requirements including
bend radii, angles, intersection points, intermediate and overall lengths, and (v) other data
necessary to define design requirements.
A matched set drawing defines items which are matched and for which replacement as a
matched set is essential.
It is prepared when the required dimensions, tolerances, or other characteristics of items can
only be specified in terms of the matched relationship.
This includes items which are interchangeable only as a set because of special requirements for
machining, electrical characteristics, performance, etc.
It includes (i) physical or functional mating characteristics of the matched items (set), (ii) unique
identifier assigned to each of the parts and to the matched set, and (iii) discrete identification
marking of the matched set.
A contour definition drawing contains the mathematical, numeric, or graphic definition required
to locate and define a contoured surface.
It does not establish item identification for the items described thereon.
It is prepared to define complex surface geometry which cannot be conveniently included in the
detail drawings of an item.
It includes (i) mathematical equations for the geometric features, (ii) tabulated coordinates, (iii)
graphic sections, and (iv) a summary of features and relationships to more basic coordinate
systems in appropriate combinations to define the contoured surface or the desired points on a
contoured surface.
A computer program drawing describes the design details, establishes item identification, and
provides for control of the software it represents.
Three types of drawings are generally used.
These are (i) computer program listing drawing, (ii) computer program assembly drawing, and
(iii) computer program set drawing.
Computer program listing drawing is prepared to document operational computer programs /
software. It provides design details and establishes item identification for the computer
program.
It identifies the master source code, object code, or both, for the computer program in human
readable form.
The drawing specifies the media materials, marking requirements, and the applicable
specifications.
The type of software tools (computer, assembler, and compiler etc.) required to produce the
object code from the source code is also specified.
The computer program assembly drawing contains computer generated load maps of computer
programs with multiple components / subprograms.
It lists each subprogram and specifies the media materials, type of equipment required to
produce the computer program, marking requirements, and applicable specifications.
It establishes item identification for the assembly process.
The computer program set drawing groups two or more individual computer programs into a set
for handling convenience.
It consists of a parts list which identifies the computer programs and applicable notes.
It establishes item identification for the set.
Modifying drawings
Modifying drawing types (altered item, selected item and modification drawings) are not used
for items made from raw or bulk materials, items purchased in bulk lengths (extrusions, channel
nuts, and hinges etc.), or such semi-processed items as blank panels, castings, and electronic
equipment drawers etc.
An altered item drawing describes the physical alteration of an existing item under the control
of another design activity.
The drawing type permits the required alteration to be performed by any competent
manufacturer including the original manufacturer, the altering design activity, or a third party.
It establishes new item identification for the altered item.
An altered item drawing includes (i) information necessary to identify the existing item prior to
alteration, including the original item identification, (ii) complete details of the alteration, (iii) a
unique identifier assigned to the altered Item, (iv) re-identification marking requirements, and a
parts list when the alteration necessitates any additional items to produce the altered item.
A selected item drawing defines refined acceptance criteria for an existing item under the
control of another design activity which requires further selection, restriction, or testing for such
characteristics as fit, tolerance, material (in cases where alternate materials are used in the
existing item), performance, reliability, etc., within the originally prescribed limits.
This drawing establishes new item identification for the selected item.
A selected item drawing is prepared when it is feasible to select from an existing group of
existing items those items which (i) meet the required characteristics for a particular application,
and (ii) pass additional tests or inspections imposed by the using design activity for
characteristics not normally specified for the original item.
The selected item drawing establishes the detailed criteria on which selection of the item is
based.
A modification drawing describes changes to items after they have been delivered.
When required for control purposes, the drawing requires re-identification of the modified item.
The drawing is prepared to add, remove, or rework items to satisfy the user’s requirements or
to incorporate mandatory changes in delivered equipment.
A modification drawing is not a substitute for existing drawing types used to produce the item
prior to modification.
Engineering changes are incorporated into the latter drawing types to the extent that future
production is to reflect the modifications.
The modification drawing includes complete information for accomplishing the changes which
includes (i) instructions for the removal or installation of affected parts, (ii) special notes, (iii)
item identification of affected items prior to modification, (iv) effectivity of the items to be
modified, (v) instructions for re-identification of modified items, (vi) dimensions necessary to
accomplish the modification, (vii) a parts list identifying all items required for the modification,
(viii) a list of special tools or equipment required, and (ix) instructions for disposition of unused
holes, wires, removed items, etc.