Simmons C.H., Dennis E.M. Manual of Engineering Drawing

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20 Manual of Engineering Drawing

Sweeps where a 2D outline is defined graphically and

then lofted or swept, by the modeller to give the outline

a uniform thickness, as the third dimension. This

produces objects of any shape in terms of the x and y

dimensions, but a constant value for the z dimension.

Sweeps can model all of those components that look

like they are extruded, or have been cut from steel

plate. For a model of a pipe a circular cross-section is

swept or moved along a centreline of any shape.

Volumes of revolution for objects the shape of which

is symmetrical about a central axis. The wheel is a

simple example of this type of 3D object. The input is

a half outline, or a cross-section through the object,

which is rotated about the axis by the modeller, to

produce a 3D illustration.

Ruled surfaces is a simple form of modelling, where

any two sections or profiles can be joined at all points

by straight lines. An airfoil, or a turbine blade is a

typical example where this method can be applied.

Examples of various methods of CAD modelling

are shown in Fig. 3.5.

needs to be designed and tenders are invited from

organizations with experience in plant construction that

would be prepared to erect the project and commission

the plant for the client in full working order according

to an agreed timetable.

On large projects several competitive quotes may

be sought from rival construction groups to be delivered

by a given date. The client will then make a choice

and all responsible parties sign legal contracts. Having

received an order to construct the plant, pipework

systems basically require two types of drawings. Flow

charts are functional diagrams showing the scheme

and will include major items of plant. This diagrammatic

arrangement is not to scale but shows the relative

positions of main items and the connections between

them. The diagram illustrates the feasibility of the

system.

Equipment may be fixed at various levels. Assuming

that a factory is to be built, then separate areas will be

allocated to individual teams of draughtsmen who

prepare layouts for structural work, manufacturing areas,

heating, ventilation, air conditioning, compressed air

and electrical services, etc. Ground site surveys are

undertaken and various datum levels established to act

as benchmarks for reference measurements. Steelwork

can now be designed for the factory and manufactured

to suit the site contours.

A 3D scale drawing could be constructed showing

separate levels on which the items of plant are mounted.

Straight lines representing the centrelines of inter-

connecting pipework are added. Pipes are sized to ensure

adequate flow of liquids or gases and to withstand the

pressure exerted by the contents. Realistic pipework

can now be added. Suitable bends, elbows and other

fittings may be directly ‘dragged and dropped’ at the

various corners where pipes change directions and

levels.

Software is available with libraries of ready-made

standard fittings. Note carefully, however, which

Standards are applicable. ISO and US standards are

regularly used and specifications need to be checked.

Ready-made welding symbols are also available.

The drawing office will be responsible for preparing

lists and schedules of equipment required for fabrication

and the following are typical:

• Pipe lists quoting sizes and lengths taking into

account bend radii. During erection, pipes are cut

to length then welded into the pipelines.

• Lists of similar standard bends and elbows.

• Lists of similar welded joints and processes.

• lists of unions joining pipes together for non-welded

constructions.

• Valves of all different types, sizes and connections,

i.e screwed, bolted and welded.

• Hangers to support pipework and expansion devices

to permit movement.

• Pumps and associated fittings.

• Instrumentation devices; pressure gauges, tempera-

ture measuring devices and flow meters and filters.

Fig. 3.5

Pipework systems

There are many aspects of pipework draughtsmanship

where the computer can considerably improve

productivity. In many cases, by using 3D modelling

software the design can be partly automated.

In a typical application a consulting engineer would

be appointed to devise an outline solution to a given

problem and prepare a specification, defining in general

terms, the scope of the job to be built. The plant system

CAD organization and applications 21

• Equipment will be ordered from manufacturers using

these records and costs calculated.

Another vital task that the computer can determine is

to check clearances where pipes cross to ensure that

there is adequate space to allow erection and operation.

The above are typical process tasks that can be

handled by piping software.

Communicating design

concepts

Mockups and prototypes

Mockups and prototypes show how products and

mechanisms look and perform but building them is a

time-consuming process. A 3D model is life-like,

popular and can be of considerable assistance for

publicity purposes especially where the client has

limited technical experience. Recent developments are

easy to use and an economical method of demonstrating

engineering design concepts.

Drawings can be communicated by email and have

the advantage that they can be viewed by anyone who

has a Windows PC. Products can be rotated through

360 degrees to show how they appear from any angle

so that movement through their cycle of operations

can be demonstrated. Simulation may be sufficient to

reduce the need for expensive prototypes.

Maximized sales and marketing opportunities may

result from presenting new and novel product designs

more effectively to customers and business prospects.

Models can shorten development cycles and assist

in fast product design changes.

Animated drawings give you the opportunity to

explode or collapse an assembly to demonstrate how

the components fit together.

Confidence in a particular project also results from

confirmation that it is acceptable and suitable in the

market place.

Production

Many products require a considerable amount of testing.

Safety is always vital and must be the top priority.

It needs to be remembered that all products must be

designed so that the production department can

economically manufacture them. The design must also

be suitable for easy assembly and repair. Financial

constraints should never be forgotten, hence meticulous

care is taken in pre-production phases to reduce the

time-to-market and eliminate modifications to the

product, once mass production begins.

Rendering controls

Presentations and proposals using photo-realistic images

add excitement and visual impact. Before applying

rendering features to a model, the background and

lighting conditions should be adjusted to simulate mood,

time and scene composition. It can also apply lighting,

shadows and ray tracing for reflective and transparent

materials, and if required, background scenery.

Smoothing areas of high contrast to improve

appearance can enhance image quality. Accuracy is

improved through fully associative design. Mating

constraints are preserved and the relationships between

parts and assemblies. Drawings update automatically.

Errors may be prevented and designs optimized by

using Collision Detection to observe in real time how

moving parts interact. Visualization may be improved

with enhanced graphical control of lights. Photo-realistic

effects may also be created by means of sophisticated

ray-traced lighting. It is also possible to analyse the

complete history of the design project and document

an automated design process.

The rendering mode quickly displays a shaded image

of the model with materials attached. It is often

convenient to save alternative production quality images

of your design for comparison purposes and use in

other associated design projects. Alternative views can

be a valuable and visible asset during training programs.

Materials options

Visual effects from libraries of life-like textures and

materials can be added to 3D models easily, using

commands available on the toolbar menu. Libraries

are available with a wide selection of plastics, metals,

woods, stones, and other textured materials which can

be applied to entire parts, features, or individual faces.

Realistic changes can also be made to suggest surface

reflectance, roughness, transparency and an irregular

or indented appearance.

Typical AutoCAD drawings

The following examples are meant to convey to the

reader the extensive range of draughting facilities

available from software associated with basic programs.

Obviously there is a certain amount of overlap in the

scope of programs and often alternative ways of

performing similar operations.

Figures 3.6 and 3.7 show pictorial drawings of an

engine development.

A pictorial view can easily be generated after drawing

orthographic views, which give the dimensions in three

planes at right angles to each other. Figure 3.8 shows

a drawing of a cycle. Figure 3.9 demonstrates the

realistic effect of rendering. The viewing point and

orientation is adjustable.

Architectural drawings for the design of a shopping

mall are reproduced in Fig. 3.10 and Fig. 3.11. They

show the outline of the development and how the

completed construction could appear.

22 Manual of Engineering Drawing

Fig. 3.6

Fig. 3.7

Fig. 3.8

Fig. 3.9 Illustrates the variety of subtle textures available within the

materials library

CAD organization and applications 23

Fig. 3.10

Fig. 3.11

24 Manual of Engineering Drawing

Figures 3.12 and 3.13 illustrate an architectural

drawing from two different viewpoints. Alternative

simulations may be used to assist the client in the

choice of colour for the finished building.

Design concepts, which are rendered clearly and

convincingly, certainly aid at the stage where decisions

need to be made to finalize aspects of shape, form and

finish. The presentation of alternative solutions using

the same master drawing is also an added bonus.

Fig. 3.12

Fig. 3.13

Engineered components are often designed for clients

without a technical background. To be able to observe

the final product in three dimensions with its approved

finish and in an ideal situation will reduce design time.

Many people have difficulty in reading drawings, but

with a presentation of an internal building detail, which

perhaps shows a slate floor, and coloured textured walls,

then the client can understand exactly how the structure

will look. The drawing bridges the communication

gap.

Creating renderings is fast and since the data required

is stored in the DWG file it cannot become separated

from the component drawing. Menus and dialogue

boxes are used. The program features include shading

and ray tracing giving shadowing, reflection and

refraction effects. A comprehensive library of materials

and textures can be used to create a variety of surfaces,

such as wood, glass, marble, granite, etc.

A wide selection of illumination tools and compat-

ibility with associated software, allows the draughtsman

to make walk-throughs, fly-throughs and animated

product-assembly presentations.

Lighting studies are easy and accurate. You can

produce a variety of artificial, natural and mixed lighting

effects. It is possible to arrange directional lights in

various combinations and locations and control such

characteristics as colour, intensity, attenuation and

shadowing.

In addition, a Sun Locator lets you work easily with

sunlight effects. You can position the sun to a specific

time of day and year to create realistic sun–shadow

combinations. The feature allows architects to calculate,

for example, whether a living room will receive enough

sunlight at midday in late December. On a larger scale,

in the design of shopping malls for example, the position

of the sun in relation to a particular area can materially

affect heating, lighting and cooling loads.

You will appreciate that these programs can help to

confirm design decisions and prevent misunderstandings

while they are still easy and inexpensive to remedy.

A perspective drawing of an internal part of a building

in Fig. 3.14 indicates the style and character of a finished

construction.

Examples of animated presentations are given in

Fig. 3.15 and Fig. 3.16. The impact and appeal of

sales iliterature is often enhanced by the use of theatrical

effects.

BS 4006 gives the specification for hand operated

square drive socket wrenches and accessories. The tools

are manufactured from chrome vanadium steel and

Fig. 3.17 and Fig. 3.18 show a presentation for a sales

catalogue.

Figure 3.19 illustrates exploded three-dimensional

views of a turbocharger for an automobile.

Figure 3.20 shows an application of AutoCAD LT

where part of an assembly drawing has been copied

into a word-processor and used to prepare a production-

engineering document.

CAD organization and applications 25

Fig. 3.14

Fig. 3.15

26 Manual of Engineering Drawing

Fig. 3.16

Fig. 3.17 BS4006 gives the dimensions, testing and design

requirements for hand-operated square drive socket wrenches and

accessories. The tools are manufactured from chrome vanadium steel

and these illustrations show typical production drawings and

presentations for sales brochures.

Fig. 3.18

CAD organization and applications 27

Fig. 3.19 Illustrates exploded three dimensional views of a turbocharger for an automobile

Fig. 3.20 Shows another application of AutoCAD LT where part of an assembly has been copied into a word-processor document and to prepare

production engineering information

28 Manual of Engineering Drawing

MechSoft

The MechSoft program contains many wizards, used

to assist in the design of a large variety of mechanical

solutions, which conform to National and Company

Standards.

The detailed component drawings are of the

parametric type; all are mechanically correct and used

to create automatically, new components. All of these

parts are compatible with the Autodesk Inventor Series.

A typical small assembly is shown in Fig. 3.21. A

gearbox is to be manufactured in a range of sizes using

standardized components. The assembly sequence

requires each of the parts to be selected from their

detail drawings. In a specific order, parts are manipulated

into position and the mating relationships tested.

Fig. 3.21a

Mechanical design checks can be undertaken at any

time throughout the design process in seconds. The

assembly is easy to create, manage, link and understand.

The entire assembly can also be modified automatically

by a change in the mechanical specification and

remodelling is almost instant.

This advance is one of the most beneficial

developments available to a designer in the area of

productivity tooling.

Further details can be obtained by contacting

sales@mechsoft.com.

The following picture gallery (Fig. 3.22) illustrates

some of the interesting developments which have taken

place with the advances in computing technology in

recent years. All of the software programs are associated

with the basic AutoCAD program. For further detailed

information visit www.autodesk.co.uk

CAD organization and applications 29

Fig. 3.21b Printed by kind permission of MechSoft.