Engineering design robert matousek

Engineering design robert matousek

P r o f esso r of Mech ics, U n iver i y of C ambri dg e

London· BL A CK I E & SON LIMITED· G l asgow

5 FIT HAR D I NGE STR T

PORTMAN SQUAR LOND O N' \V I

BI S H Pl RIGGS G L ASG OW

BLACK I E & SO ( NDIA) LIMI T D

-103 -5 FORT S T REE T

BOMB A

T e G e rma n e d i ion o f t his bo ok e n t tle d

' K onst r u kt io s l eh r des al l g eme in e" Masc hi nen ba ue '

TO THE ENGLISH EDITION

The subject of design in engineering occasions much discussion at thepresent time.It is said by many that fartoo few trained engineers inthis countrywish to devote themselves to it and by some that there is insufficient teaching ofdesign in our academic institutions The position in Germany is different becausethere engineering education has, by tradition, a considerable design content Thisaccounts for thefactthat the present book was firstpublished in that country;there is,so far as I know,no comparable English tex

It is hoped that this translation will help students and others here to thinkmore ab ut design.In particular it may be of interest in the Colleges of Advanced

Te hnology, where new forms of engineering education may be expected toevolve inthe coming years

D. C.J ohnson Cambridge

Autumn 1962

41A Planned Policyfor theDesigner 26

A The Systematic Working Plan

The types of pro lem to besolved p28-Exercise problems I, 2 p36

Howarethevarious possible solutions found? p38-How isthebetsolutionfound? p4 - The evaluaton schemep43 - Exercise problems 3-7p 49

What doesthe designer have to bear in mind inform design? p64-General

points regarding form deign p65

I How the basic deign influences form design p6

2 How mechanical loading influences form designp66-Rules p72-Exercise

problems 8 and 9p 5

3 Influence of material on form design p75

4 How the production method influences form design p7

( 0 ) Form deign of grey iron castngsp 6-Rules p90-Exercise problems

10 - 1 5 p 9

vii

(b) Form design of steel castings p93-Rules p98-Exercise problems

(e) Form design of pressure die castings pI12-Rules p 23

(J) Form design of plastics mouldings p 123- Rules p 127

(g) Form design of welded fabrications p127-General p 127 - Welding cessespI28 - Gas or arc welding pI29-Weld forms pI30-Stre s s

pro-pJ32-Measures to combat contractio stress pJ35-Joints used inweldingp 13 8 - Weldability of steelsp143- Design of welded structuresp144-RuJe p146-Exercise problems 19-23 pI47

(h) Form design of forgings p148

Hammer forgingp148- Principles of form designp149- Rulesp

157-Exercise problems 24 - 26 pI5 -Drop forging pI59-Rules

p164-Casting, forging, or welding? p164

(I) Desig in for manufacture by machining methods pI67

Designing for machinability pI68-Designing for economy pI7l

-Designing forc1ampability pI74-Designing for existing tool equipmentpI76-Designing to avoid redundant fispI76-Designing for accessi-

bility p176 -De s igning for ease of assembly p176

5 How the space factor influences form design p1 8 -Exercise problems

27 and 28 pI84

7 How weight influences form design (lghtweight construction) p186

(a) Optimization of form (lightweight construction) p187-Rules

p199-Exercise problem 2 p 20 0

(b) Best possible estimate of strength p 2 00

(c) Use of welding instead of riveting p202-Exercise problem 30 p204

(d) Us of welding instead of casting (lightweight co struction in steel)

p 04-Exercise problem 31p 06

(e) Us ofhigh-grade ste lp 0 -Exercis problem 32p 09

(f) Use of lightweight materials p 09

(g) Use of special sctions p213

(h) Use of newcomponents p2 1

( i ) Saving of weight through basic change oflayout p21 8

(k) Lightweight construction by appropriate choice of parameter p219

8 How the us ofstandard components influences form design p220

9 How existing products influence form design p222

10 How appearance influences form design p2 22

11 How convenience of handling influences form design p 2 8

12 How maintenance questions influence form design p22

13 How the question of repair influences form design p22

14 How surface properties influence form design p229

1 How fitness for shipment influences form design p 230

1 How power requirements influence form design p230

inter-his par often fails to attract for the designer the prestige which is his due,

it must be pointed out that he has the very responsible task of satisfying

in the best manner possible the conditio s laid down in the customer'sorder, and thereby pro iding the essential fo n atio for economic

manufacture The finest workshop facilities with the most up-to-date

machine to ls enabling e o omic manufacturing metho s to be used are

of no avail if the desig er has not done his work satsfactor y

High-grade work on the sh p floor is only possible if the design

itself isgood Again, even the best of salesmen is powerless if the desig er

has n t approached his task with due regard for economic factors and

in the art of design For the same reason, large industrial concerns began

many years ago to compie sets of examples of " good" and "bad ,

practice to keep their engineers' attention focused on some of the rules

to be observed if a design is to be successful from the viewp int of-pro

-d ction, assembly, etc Man component manufacturers publish g idesfor the use of designers who wish to utiliz their components This

ap lies, for instance, to rolling bearin s, belts and chain drives, and oil

seals In recent years, aspects of the pro blems concerned with appropriatechoic of material and correct design have been discussed again and

again in jo rnals an books-proof of the importanc atta hed tosuccessful effort in the field of design

There are some students of mechanical engineering who say: "Whyshould I have anythin to d with design, after all I'm going into theproduction or the sales side" Such students have not yet recognizedthe advantages to be derived from a study of design problems It is for

this reason that many firms of wide experience insist that newly appointedjunior engineers shall first spend some time in the drawing office beforepassing on to the works or into other departments.

An engineer in the shops who has had design training will approachproduction work with a quite different understanding and will savehimself the trouble cf querying many points with the design office Is

it possible to imagine an engineer who would offer an expert opinion,

yet who had no idea of the working principle of the machine in question,

or of the operaton of its various components, or of the advantages and

disadvantages of given desig arrangements? I is often necessary for arepresentative to give information on design details to a customer

familiar with technicalities, and indeed, even the drawing office itself

will often call for design sug estions from one of the firm's representatives

For an engineer in an administrative post not the least valuable asset

of his drawing office ex erience is the appreciation that he gains that

design is a resp nsible and intellectually demanding task which cannot

be undertaken as if it were merely routine work

Duly recognizing how important design ex erience is for all engineers,the Verb and Deutscher Elektrotechniker* has issued a memorandum onthe taining of electrical engineers which contains the following passage:Design is of the utmost importance in thetraining of ane gineer, no matter inwhatfield of activity he may subsequ nty be employed A student who hasreached a certainstandard of capability in designa d has foundpleasure in it wi find tbings considerablyeasier whenbe starts work, eventhoug th path he takes does notlead to the drawingoffice For many top posts this isetremely important The lack of adequate desigcap bility isa deficiency which can be made good only in ex eptional cases Manyoutstanding men confirm again and again that the themselves h ve derived great

avantage from having spentseveral years inthe drawin office, and their experienceshows thata good courseofdesignpractice undertaken asa part of technicaltraininexerts a beneficial effect ona engin er's workat all times,regardlessof whether he isemployed in the planning de artment, on production, in the laboratory, or on themanagement side

It is therefore easy to understand why, in most ad ertised vacanciesfor junior engineers, great importance is attached to thorough training

in design

• Equivalent o f B rit i s h In st it utio n o f E lectri cal Engineers.

I GENERAL ASPECTS OF THE DESIGNER'S WORKWhat is meant by desig ?

An observer watching a designer at work will note that when starting

on a new assignment he first of all makes a close study of the conditions

to be fulfilled He then ponders the problem for some time before preparing one or more simple schematic diagrams Perhaps he will also

-take up his slide rule to check quickly some of the figures involved beforeresuming consideratio of the various possible solutions Not until theunit or machine has taken shape in his mind does he decide to makeseveral different properly-scaled views of it by a process of alternate

c lculation and drawing While thus engaged, however, he has still toconsider which material is most suiable, which manufacturing method

is most economical, and how the method finally chosen will affect the

desig These, and many other p ints besides, must al be taken intoaccou t Enough has already been said to show that designing is forthe most part a purely intellectual, and indeed creative, activity which,contrary to the popularly held view, cannot be regarded solely as

draughtsmanship

-The designer is also often widely referred to as a draughtsman.Draughting, however, denotes only that aspect of designing or planningwhich is concerned with the actual preparation of drawings Not untithe design has developed into a clear picture as seen by the mind's eye-and every design is formed in the mind to begin with-can itbe drau hted

o paper

Nor can planning be used as an alternative term for design Planning

is rather the preparatio of schemes for the use of land, buildings, and

industrial equipment

It will be seen, therefore, that it is not easy to define design activity

in a way which covers all the aspects One thing is certain-in designthe main burden of the creative work done is undoubtedly intellectual

in nature, and it is intellectual activity of an extremely complex kin Viewed from a higher vantage p int it certainly includes all design pro-

cedures, the pure craft activity of drawing, consideratio s of various

kinds-physical, technological, productio en ineering, mathematical,

and economic-as well as the purely formative activity

The art of designing can perhaps be explained o the following lines

3

The d es i g ner use s h is i nte ll ec tual ab i t y to appl y s cient f iic k no w l edge

t o t h e t ask of cre a t ng t h e draw i ngs w h ic h enable an e n gi n ee ri ng p ro d uct

to be m a e in a way t h t no t o nl y m eets t h e s t ip ul a t ed con dit i o ns b ut a ls o

p e rmits manufa c ture by t h e most econo m ic met ho d.

What kinds of design w o rk are ther e ?

As in every field of human activity so also in design work there aredifferent degrees of difficuly

In practice thekinds usually recognized are adaptivedesigns, develo ed

designs, and new designs

Adapt i v d e si g

In the great majority of instances the desig er's work will be con

-cerned with adaptation of existing designs There are branches of man

u-facture where development has practically ceased, so that there is hardly

an thin left for the designer to d except make minor modificatio s,

usually i the dimensions of the product Design activity of this kindtherefore demands no special k owledge or skil, and the problems

presented are easiy solved by a designer with ordinary technical trainin

I have often been asked by engineers why I am not content to allow

students to c design" from proven existing models This question will

be considered later, but the principal reason is that such a method pletely fais to tain the desig capabilities of the student engineer

com-The man who is accustomed to working entirely from existing designs,

and who is therefore sometimes called a " pantograph designer ", will

not learn to appreciate what designing means u til he is confronted with

a task requiring original thought, no matter how simple it may be Of

course every beginner must fist prove his worth in the field of adaptve

design Unfortunately many" desig ers" do not get any further

A rather higher standard ofdesign ability is called for when it becomes

necessary to modify the proven existing designs to bring them into line

with a new idea by switching to a new material, for example, or to a

different method of manufacture Examples of this will be given in a

later section

D ev e l op me n t d e sig n

Considerably more scientific trainin and design ability are needed

for development design Althou h here, too, the designer starts from an

existin design, the final outcome may differ quite markedly from the

initial pro uct

fuly wihout a precedent.

Organization of the drawing office

In practic it has become customary to use different professional

titles corresponding to the various levels of design activity

The adjoinin diagram (fig 1) sets out the organization of the staffresponsible for design work in a drawing office

Assistant Designer

I

Designer Draughtsman

F i g I - O rga ni za tion o f per s onn e l in a d r a w in g of f ice

According to a proposal of the professional institution of Germanengineers, the term d e s i gn e ng i neer sh uld be ap lied only to engineers

who are engaged on design and who, by virtue of special natural giftsand an excellent knowledge of mathematics, physics, and engineering, arequalified in the best sense to undertake entirely independent work

These are qualities which are certainly called for in a chief designer(wh may also' be a director), head of department, chief en ineer, anddeputy chief engineer, that is to say in those engineers who also have to

c rry a large me sure of responsibiity Heads of sections sh uld alsohave some ability to work without guidance and the capacity to resolve

problems without an existing design to copy

A detail designer, on the other hand, needs only an ordinary standard

of professional taining on the lines provided, for example, by a technicalinstitute.

It is not intended to imply, however, that engineers trained in this

way are not suited to become design engineers Indeed, it is a fa t con

-firmed b experience that many who have passed engineering schoolcourses are doing outstanding work as design engineers in highly respon-

sible positions

The engineering draughtsman and the trainee designer are usually

ambitious juniors who have been transferred from the shop to the drawing

office for training which is carried out there and by attendance at a

technic l college

A point which should not be -le ft u mentioned is that in industryappointments to senior design posts are not made on academic qualifica-

tions alone; only knowledge and ability are decisive and are made so by

the uncompromising demands of industrial practice Anyone possessing

the enthusiasm and drive to improve his knowledge can certainly advancefrom the position of draughtsman to that of an independent desig er.Relationship between the drawin office and other departments

The two principal areas of technical creative activiy are d esign and prod ction. The importance of the creative work of the desig er is

apparent from the sin le fa t that he is resp nsible for putting the

engineering product into such a form that it can be manufactured in the

most economic l way Design and production are therefore seen to be

closely interrelated This fact has led to the practice, n w common inmany works, of bringing the responsible executives together from time

to time for an interchange of ex erience with the design engineers

But there are also reciprocal relations between other departments of

a factory and the drawing office Results obtained in the test department

can often lead to major improvements, or perhaps the design principles

of a new product have still to be worked out That the closest of relatio

n-ships must exist between the development engineer-or his department

if the works is a large one-and the drawing office goes without saying

From the sales engineer, too, the designer can often hear of vitally

important points of view which will influence his work

Official reg lations sometimes playa decisive par in determining

desig ; in this connection one need only think of the reg lations for

steam boilers as laid down by the authorities responsible for structural

safety and fire prevention

The drawing office must of course maintain the closest contact withthe customer to ensure that his requirements are clearly understood andcatered for as fully as possible

The various interrelationships involved are shown in diagrammaticform in fig 2.

Fig 2.-Relation betw e en the drawin g of fi ce and other departments

Wby teach design as a special subject?

During his training in the various fields of knowledge the youngengineer is crammed with a vast amount of theoretical material andinformation He only realizes his helplessness when he is faced with thetask of logically applying what he has learned to a specific end So long

as his work is based on familiar models or previous designs, the knowledge

he possesses is perfectly adequate to enable him to find a solution onconventional lines As soon as he is required to develop somethingalready in existence to a more advanced stage, however, or to createsomething entirely new without a previous design to guide him, he wilfail miserably unless he has consolidated his knowledge in depth and soworked upon it that he has reached a higher level of understanding Adetail designer can manage, if he must, with knowledge pure and simple.The design engineer, on the other hand, must have learned to thinkindependently, to reduce logically and to draw conclusions, and to com-bine There are many who believe they can acquire all this by attendinglectures and reading textbooks What they fail to realize, however, isthat they are only accumulating one fresh item of knowledge after another.Understanding, coupled with powers of logical deduction and judgment

is not a capability that can be conferred from outside; on the contrary

it is something purely personal and inward acquired only by diligent

thinking and working with the knowledge already possessed As mentionedearlier, it is a basic pre-condition for independent designing, and ispossession qualifies the designer assisted by a lively imagination to dooriginal work.

In the past, instruction in designing was given by setting the student aproblem concerned with the design of prime movers and driven machines.Without any further preparation in design thinking he was then left alonewith the problem The result was that the student looked aroun for agood existing design, and, having fou d it, proceeded to work out some

le ding dimensions; this done, he would start to reproduce the original.The value of such pantograph work as an intellectual exercise was exceed-ingly small, for the student had no need to ra k his brains any furtherabout the construction of the machine or about the kinematic interplay ofthe varous components, or ab ut the form given to the compo ents, orabout problems associated with materials and manufacturing methods-the ready-made answer to all these points lay in the original design The

p ints to be considered in the design had already been worked out,probably by generations of designers in a process of laborious study andpainful experience It isobvious that this method of teaching design onlyturns the beginner into a copyist, a painter of portraits, because he is

ig orant ofthe entire complex of design thinking

Even when the beginner is set a problem involving the use of anexisting design, he must ask himself the question: Where and how shal

Istart? This is where the first difficulty makes is appearance Usually hewill begin by looking around for formulae and win discover that he mustuse his own discretion in emplo ing the rules of mechanics, kinematics,etc The groping around, and the trial-and-error methods typical of thebeginner, are responsible for the view that designing is essentially in-tuiive More particulary, it is constantly being emphasized in thisconnection that designers are born, not made, or in other words that onemust be talented for the part This, however, is an ob ious requirement

No one will dispute that al intellectual and manual occupations call fortalent The high qualities required of the designer in this respect in par-

Those who are co tinually pointing o t that designing cals for a specialtalent are giving expression to the view that designing cannot be taught

An analysis of design work carried out from the professional side has led

in the last decade or two to re ognition of the fact that the technique ofdesigning can also be tau ht systematically in just the same way as thebasic technicalities of all other professions are systematically imparted atschools and colleges

In connection with the tainin of desig ers one ofen hears it o jected,

particularly by students who re lize their own shortage of alent and wouldlike design to involve no more than copying from an original, that desig -ing issomethin one can only learn through practical experience Agreed!Mastery does indeed depend on a gre t deal of exercise with practicalproblems But this applies equally to all other professions Whoever iscontent to copy existing designs year after year, h wever, will never reachthe status of the independent designer.

Manufa turing processes have already been perfected to a degree thatguarantees optimum output per unit oftime in return for minimum outlay.The designer who fails to provide a basis for economic manufacture hasnot kept abreast of developments in production The great diversity ofthe solutions presented in answer to a specific problem involvin closely

cicumscribed conditions is indeed proof that designers are often in someuncertainty about the number of available methods most capable ofserving the required purpose, and that inmany instances they are still verymuch in the dark about the extent to which choice of material, productdesig , and component arrangement c n cheapen manufacture, simplify

assembly, and promote reliability, etc

It would be a mistake to overook the co siderable progress that hasalready been made in educating the young designer in rational methods

of workin The same problem forms the subject of many articles intechnical journals and books For the beginner, however, it is difficult todistinguish what ideas are fundamental in such an abundance of published

material Above al there is the lack of examples for practice A set of

" wrong" and" right" examples or a list of design rules cannot bythemselves cultivate in the beginner the habit of methodical planned thinking

-The advantage of working to a properly directed plan lies mainly inthe avoidance of all superfluous repetitions The man who pursues anaccidentally discovered solution without considering the consequenceswill often find that he has stayed into a blind alley and must start again

at the beginning, Only byworking to a methodical plan can the designerhope to escape unwelcome surprises of this kind By adopting the rightmethod of working and thinking carefully ab ut i he can save time, avoidwasteful mental effort and thereby increase the efe tiveness of his work.One point must be emphasized without delay Anyone who imaginesthat working to a method is a welcome opporunity whereb even a subjectlike design can be learned with minimum outlay of mental effort and

wihout in ependent thinking will be quickly and profoundly disa.pointed A methodical plan of working does not offer a substitute forintellectual abiities like imaginative power, logical thin ing, co cen-

p-tation, the gift of combining ideas, and an inventive mind It only p intsthe way

II THE DESIGNER

Qualities required in a designer

Every student who wants to become a designer should bear in mindthat design calls not only for absolutely clear-cut and purposeful in-

tellectual activity, but also for an inventive and intuitive mind allied to awhole series of character-based and personal qualities These qualities,however, are not c pable of being acquired, but have their origin in aspecial endowment of the individual

The following list gives a survey of the capabilities and qualitiesneeded by the successful designer

1.Caa ity to visualiz bodies, static forces and stresses, d namic phenomena,

h draulic forcs andflowconditions, elet cland thermal phenomena

2 Integratn c p city

3 Ability to think logically

4 Ability to concentrate

15 Ability tospeak andwrite skilfully

1 Capa c ity to visualize

A well-developed capacity for visualizing is one of the basic ments of the engineering profession, and particularly of the designer Hiscreatio s are always bodies composed of the simplest posible basic forms,such as right cylinders, cones, and spheres which he shapes, works upon,and assembles in his mind before putting them down on paper in the form

require-of drawings The designer must also have the imaginative resources toappreciate the interaction of components, the transmissio of forcesthroug them, the distribution of internal stresses, and all the physicalphenomena occurring in a machine or piece of equipment

Naturally, there are different degrees of this ability Even of a beginner,however, it must be expected that he will at least have the ability to

10

imagine simple basic forms and thei combinatio s, interpenetrations

and sections Those who find it necessary even at this stage to use models

to assist their imagination will never reach the status of the independentdesigner Even the engineering drau htsman ne ds a certain imaginativepower

2 Integrating capacity

The capaciy to visualize and the capacity tointegrate are major constituents of a creative imagination for which the designer must have a certainnatural aptitude All machines and industrial products consist of known

-basic structural elements By combining these elements the designer iscontinually creating new forms to serve specific ends, even when there are

no pre-existing designs to guide him, It is also an established fact that bysuitably combining existing inventions it is possible to evolve somethingentirely new which isin its turn patentable Only b the skilful exploitation

of natural laws can the designer make the effects of the laws serve his plans

3 Abi l ity to t hink l ogica l ly

The intellect must be fre d for concentrated productive thinking b

eliminating to the fullest possible extent allunprofitable intermediate tasks

of secondary importance and all distracting influences This calls for theposses ion of highly developed intellectual powers on the par of thedesig er He must beable tojudge correctly the interrelationship between

c use and efect, and to distinguish essentals from non-essentials Hisjudgment of the nature and magnitude of the various influences resultingfrom the different factors involved in a tech ic l phenomenon must bestraightforward an clear-cut

A point which must be given special emphasis at this stage is that in

only a part of his deliberato s and de isio -making can he call on theassistance of mathematics His intellectual activity often consists in the

abundant use of ordinary clear-sighted common sense

The possession of this natural gift istherefore the main factor in deciding the extent of a designer's capability to re ch the right solution to avariety of problems, to findmeans of making improvements, or to indicatenew and improved ways to attain a specific goal

-4 Ab il ity to concentr a t e

Ail successful intele tual activity c lls for exclusive pre-occupation of

the individual's entire thinkin c pacity with, the problem o which he is

engaged Design thinking likewise demands very intense concentration at

a high level The necessary capability for this can only be acquired by longpractice Nervy, excitable, and restless individuals never learn the art

5 I nve nt ive t al e nt

Most people regard an inventor with a certain awe They imagine thatthe object invented is a kind of sudden revelation manifested by a specialintuitive talent Of course no one would deny that inventing calls for acertain natural endowmen But this consists in the inventor's ability,

based o clear logical understanding, toad ance stage bystage by judging,

deducing, and combining until he achieves something new, an invention

in fa t, alh u h in some circumstances he may not be able to recollectthe process by which he reached hisgoal

Reuleau has noted that, "in inventing, one idea continually givesrise to another so that a veritable step-ladder of ideas is negotiated beforethe objective is reached.-There is no evidence of inspirato or flashe

familiar mental images to form a new product If the inventive spirit is

made to serve rigoro s purposeful activiy in the design field, it is to be

welcomed without qualification

There are, however, designers who appear to be obsessed with invent

-ing and who are constanty putting forward newideas A special warning

is needed against this sort of passion It is only very rarely that theinventor derives an financial success from it Krupp has said that" a

g o desig er fin s it easier to move, thro gh the fruits of his labour,

fom the garret to the drawing room than d es an inventor The latter

usually lands out of the drawing room into the garret."

6 Memo r y

Like allwho work with their brains, the designer also needs amemory

of average capacity In the first place, of course, he needs this for studyin

the underlying sciences In addition, part of the mental equipment ofthe

designer consists ofa vast amount of facts and figures which he must have

at his finger tps aU the time wihout needing to co sult books A good

memory also helpshim overaperiod of time to amas a store ofexperience

which willbe of value to him in later design work

.No less important than his intellectual c pabilities are his personalcharacteristics Despite their importance in his later professio al life, it

is unfortunately just these qualities which receive so little training andobservation during the designer's student period The beginner might

therefore gain the impression that the qualities which make up his characterare not so very important However, there are many who have blunderedthrough lacking these qualities and who have found the greatest difficulty

in retrieving their lost confidence

7 Conscientiousness

One of the principal characteristics, and one which can rightly bedemanded from ajunior draughtsman, is the ability to work th ro ghly

and co scientiously The smallest error which finds its way from the

drawing office into the shops can cause very serious harm under modern

conditions of batch or mass production It can also happen, however, that

certain of the designer's oversights, such as unsuitable choice of material,

or insufficiently generous dimensioning of parts, fai to make themselves

apparent in the production shops This sort ofthing iseven worse, be ause

complaints from customers are harmful to afirm's reputation A designer

wh makes mistakes of this kind soon forfeits the prestige he enjoys

8 Sense of responsibility

An independent designer lacking the courage to accept responsibility

isunthinkable Courage of this kind springs from the sel confidence which

a designer possesses when hehas complete mastery of his subject He who

la ks the inner compulsion to acquire intellectual independence and assume

resp nsibility had better give up any cherished ideas of professional a

d-vancement

9 Integrity

Young designers are usually lost in admiration of the outcome of their

firstefforts at desig and are therefore quite disheartened when correcto s

are made to their work Integrity towards himsel demands from the

desig er that he shall also have the courage to be self-critical of his work

which, after all, is to be considered as no more than an approximation tothe ideal solution and therefore always capable of still further improve-ment When judging the work of others, h wever, it is best to refrain

fom criticism if one is not in a position to offer a better solution

10 P erseverance '

It must be admitted that even in the field of design there are man

tasks which are not in themselves ofabsorbing interest as mental exercises,

and which for this reason are considered boring Instances of these arethe calculaton of the weight of the many components which make up a

vehicle, or the determinatio of the positio of centre of gravity One

sh uld remind· oneself, however, that even tasks like these must be per

-formed for the sake of the design generally; this will induce the rightattitude of mind and the perseverance needed to cope with them.

1 1 St r engt h of wi ll

There is not a single designer who would not give thanks for his pro

-fessional success to his exercise of will and to his powers of initiative andenterprise Many examples in the history of engineering confirm that it

was the strong-willed engineers in particular who achieved success andrecognition in the face of all the objections and opp sition they en-

countered

12 Aesthetic sense

It has been said that everything which fits its purpose looks attractive.This, however, could mislead one into thinking that all one need do toobtain beautful and attractive forms is to design to suit the purposeconcerned Although this is largely true, there remain u fortunatelyplenty of instances in which the designer must also rely on his aesthetic

sense On these occasions the designer with a marked sense of aesthetic

values wil benefit greatly in his work

1 Tempe r ament

As stated earlier, an overwrought nervy individual is no more suiedthan the phlegmatic type for an occupaton like designing which calls intoplay qualities of intellect and character, as wel as personal attributes

What is needed in a designer, therefore, is a harmonio s and balanced

temperament

14 Per onality

A designer occupying a position as section leader, departmental head,

or chief designer, and therefore senior to many others, needs a quality

which istaken for granted in every salesman, namely a positive presencand skill in dealing with the people he meets professionally owing to theimporant position he holds He also needs some ability to judge character,

so that he will be able to put the right man in the right job in his office andthus ensure fruitful cooperation

1 5 Abi li ty to speak a nd w r ite ski l fu ll y

It is perhaps be ause of the quiet intelectual nature of their work that

one so often meets designers who are unable to present their views fluentlywhen the occasion arises And it is the most capable ones who find, time

after tme, that their far-sighted and progressive work often runs into the

most violent oppositon The designer who wants to make his views pre

-vail in tills situation must be able to apply to the task all his skill in speaking and writing.

-W bat is a designer expected to kno w ?

Every brain worker needs to have a certain store of knowledge for use

in his job Considered by itself this knowledge would have very little value.Onlyin conjunction with ability, systematic logical thinking, and the power

to combine, judge, and deduce does it provide him with the means to do

successful work

For the desig er, too, the information which he has accumulated in the

various areas of kn wledge forms the es ential basis of ills professional

a tivity What, then, are these areas of knowledge? For practical purposesthe disciplines involved are the ones he acquires during his studies, rangingfrom mathematics to economics and management studies

The following list gives a guide to the areas of knowledge of primary

importance to the desig er

Mechanics: Sol ids(statics, stren th ofmaterials, and dy amics)

Liquids (hy rostatics, h draulics)Gass (a rostatcs, aerodynamics, thermod namics)Electrici ty

Lig tSoundInorganic andorganic (fundamentals)Properties ofmaterials (physicl and chemical)Manufacturing processes (non-cutting, cutting, short-run andmassproduction)

Machine drawingMachine componentsPrimemoversMechanismPower transmissio

The fist stage in a desig er's training consists inthe acquisi o of theknowledge and information whereby these disciplines are imparted Hewill only derive value from them, however, if he continues to work uponthe subject matter un er the stimulus of questio s and pro lems posed by

himself until he has struggled through to sovereign mastery in the vario s

fields Arrived at the second stage of his intelle tual development, he now

also recogniz s the great extent of relationships and interdependencies,

and realizes that all the disciplines form an organic whole in so far as his

profession isconcerned

It is now time to discuss some of the factors which are imporant for

the young designer

1 Mat h em a tic s

The big ad antage gained bythe user ofmathematics isthat the subject

te ches the habit of systematic and logic l thinking For the designer,however, mathematics takes on a special importance, for it forms thefoundation of many other special areas of engineerin science Mastery

of mathematical laws and operations provides the mental equipmentneeded for investigating the laws governing the various physical quantities,and for applying the knowledge gained in this way to the solution of thedesigner's problems

The next point, which has already been made on a previous page, is

this It must not be expected that all design problems c n be solved withthe aid of mathematical concepts and proced res The beginner is very

liable to fal into this error One notices constantly that beginners starting

work on a design problem search eagery for formulae which will providethe solution, instead of first giving their common sense a chance to speak.Design problems which can be dealt with by the use of a certain mathe-

matical formula, such as a design for a flywheel or for the blading of a

fan, are therefore just what the beginner wants The rising young designer

soon disco ers, h wever, that problems permitting satisfactory solution by

c lculatio are comparatively rare, and that often it isjust the problems

presenting the greatest difficuly which are not amenable to mathematicaltreatment and have to be solved b mental activity of another kind.For adetail designer or head of section a knowledge of ordinary higher

mathematics is usually sufficient On the other hand, a designer workingindependently and obliged to include the study of modern research work

in the scope of his activities is forced to enlarge his mathematical knowledge accordingly

-De sc rip t v ge ometry - The basic pre-condition for all design activity

is, as mentioned previously, a good c pacity for visualzing in threedimensions, and this remains true no matter whether the problem involvessolid bodies, kinematic relationships, the action of forces, the distribution

of stresses or fluid- ow phenomena This capability, which, to a cerain

degree, must be inb rn in the desig er, can be developed by systematicwork A good way to start is b doing exercises in the perspe tive or

axometric representation of bodies, the useof orthographic projection with

front view, plan, and side view being introduced later or at the same time

There are times, of course, when the designer resorts to a mo el for

practical assistance The usual reason for doing this istoclarify very com

-plex three-dimensional layouts which raise problems of accessibility orfeasibility of assembly in some already highly compact mechanical unit

Atempts to solve problems of this kind by graphical meth ds are often

futile A familiar example, of course, is provided by the automobileindustry where models are used in order to give the fullest possibleimpression of the aesthetic aspect of the body design.

The " reading" of technical drawings showing complicated layouts

is something to which considerable time must often be devoted before a

clear idea of the object portrayed can be formed This is why many firmsseek to aid'understanding by adding to the working drawing an axometricview to enable the men in the shops to form an immediate picture of theitem concerned

2 Physics

"The whole of engineering is only applied physics." These wordsindicate the importance of the subject in the professional activity of theengineer The branches of physics of special interest to the engineer ingeneral and to the designer in particular have developed into specializedforms for engineering p rposes These subjects are dealt with in speciallectures which cater for the work which the designer will subsequently do.The subjects concerned are the mechanics of solid, liquid, and gaseousmedia, electricity, etc An important point is that the engineer intending

to take up designing should not only be familiar with the laws, but shouldalso make appropriate allowance for them at the right stage in his designwork Experience shows that this is not an easy matter and that it callsfor an intense appreciation of physical phenomena Since one can usuallyobserve only the effects and not the causes, it is necessary for the designer

to form clear mental images of concepts like mass, force, inertia, friction,spin, thermal conduction, so that he can successfully tackle the taskawaiting solution

3 Chemistry

There are some engineers who attach little importance to chemicalknowledge They take the view that a designer only needs to know aboutthe physical properties of construction materials and the various ways ofworking them However, the engineer must also know about the structure

of materials, their chemical behaviour, and their aggregate changes And

it is for this reason that he needs a knowledge of the fundamentals ofinorganic and organic chemistry

and all the aids thereto It is a recognized fact that the beginner shouldaccumulate some experience in this field during his practical training before

he starts his studies Experience gained in this way, however, is not ficient for design purposes, since during this early period the student willusually lack the necessary scientific basis for a deeper understanding oftechnological considerations and processes In addition, the manufactur-ing techniques and high-performance special-purpose machine tools serving

suf-mas -production ends are constantly undergoing further development and

advancement It is therefore essential that the designer should keep up to

date by continuous study of the relevant literature and discussion withstaff in the shops

a satisfactory drawing suitable for workshop use, provided that he is givenall the information necessary for the purpose This book assumes such acapability Instruction in machine drawing is given in a number of goodtextbooks

Machine elements -Every industrial product, no matter how large itmay be, consists of a large or small number of individual components,known as e lements, on the proper design and coordination of which theaction of the whole depends On closer study it is immediately obvious

that a large number of such elements continually recur in the same role,although of course the shapes given to them and the materials and dimen-sions used are determined to a decisive extent by the special features ofthe application concerned Most of these elements can therefore bebrought to a common denominator, so that all that is left is a compar-atively small number of basic forms

Knowledge of these elements isof the utmost importance to subsequent

design activity There is an extensive literature available to the designer

• T he t e mfo rm d e i g n is u se d he r e a s a tr a s l at i o o f UG e t a l un g ". Thi s w or d , a n d a ls o t h e wor d

v Ko st u t o " ,ca n b e t ra ns l a t e d d es i g b t i n Ger m a n t he c o nn o t a o s a re dif fere nt K o s tr uk ti n

i s u sed in a ge n e a l s n s e re fe r i n t o t h e wh ole plann i ng ope r at i o s o f a m a c h ine G t a l tu n r ef e

t o t h e d e ig o f a s in g l e m a c h i n e me m be r I t s d e i r a bl e t o pr e rv e t he s di s tincti o s of m e a in g , a nd

th e ter mfor m de s i g i s ac o rdin g l y u se d thr o g o ut th is b oo k

on this subject Unfortunately most of these works concentrate onmathematical treatment and ignore the many factors to be considered indesigning.

Kinematics.-Where new designs are concerned it is of the utmostimportance to know all the possible solutions capable of providing aspecific effect, so that the best one can be selected from them Kinematics,and synthesis in particular, shows the designer ways and means of findingsuch mechanisms Consequently he must devote special attention to thisstudy

Theory of form design - There was a time when it was thought that theengineering student could be introduced to the mysteries of designing byteaching him form design There is plenty of published work on thissubject Form design, however, is only a part of the designer's activityand the" theory of form design" on its own is therefore not a suitableway of acquiring a comprehensive knowledge of design work Designingcovers all considerations and measures from the placing of the order rightthrough to the graphical formulation of the solution in a manner fit forpresentation to the shops

Lightweight construction is concerned with designing with particularattention to the weight factor Questions of this kind can only be handled

by a man who is already familiar with the whole range of tasks implicit

in design activity

Design of prime movers and of driven machines is a subject, so one wouldimagine, which ought to offer the opportunity of learning design in its fullrange and scope In actual fact, however, the situation is unfortunatelyone in which only design exercises are carried out on the basis of existingexamples, so that the student designer has no need to rack his brains aboutthe kinematic layout or materials or manufacturing and design problems.All that he needs to do is to take some of the leading dimensions and scalethe existing design up or down It is obvious that by this sort of copying

no one can ever learn to appreciate design considerations or receive thetraining needed to produce an independent designer Even now, to thebest of the writer's knowledge, there is not a single technical college any-where in Great Britain or in Germany which teaches the science of design

as a single subject according to a systematic plan Is it to be wondered atthat industry complains about shortcomings in the training of designers?Not for this reason alone has an attempt been made in the chapters whichfollow to present a methodical work-plan for the designer illustrated bysimple exercises

Before concluding these remarks on the essential intellectual ment of the designer, reference must be made to one further importantfactor There are some areas of knowledge which are already fairly

equip-complete in themselves, such as mathematics, mechanics, dynamics,

h draulics, etc., at least in so far as they enter into design The chemicalindustry, on the other hand, isconstantly supplying us with new materials,

and new and better production methods and machine tools are always

being developed Engineering is engaged in rapid development scarcely

to bematched byany other profession This means that if a designer were

to content himself with what he le rned at college he would very soon bebehind the times To keep up to date with engineering advances he mustgive his attention to technical journals and make a study of patents whichconcern him He must also make it his business to apply for copies of

c talogues and leaflets for information purposes, and to collect diagrams

and notes regarding observations and new knowledge which he has gained

at lectures and exhibitions

III DESIGN FACTORS

A rational working plan for the drawing office

The planned work of the designer should cover the whole of his

activity in the drawing office:

1 His purely intellectually creative work, in other words the activity

generaly termed design and comprising the system of working discussed

in more detail in the pages which follow

2 The organizational measures adopted in the drawing office, such as

the sequencing and distribution of design tasks so as to facilitate properly

planned preparation of the work for the shops, combined with speedycompletion of the order This planning of the work cannot be carried out

at college, since the conditions for it are lacking An attentive beginner,however, will soon learn i in practice

Overall design is best left in one pair of hands, or at least supervised

by a single design engineer The tasks involved in this, starting from the

pro lem to be solved, are the de ision to use agiven layout, the choosing

of appropriate materials and suitable manufacturing methods, and thedesigning of individual parts at least to a sufficienty advanced stage toensure that no further difficulties will be encountered during full elabora-

ton or detail work

When the work reaches this stage the design engineer in charge splits

up the further detailing work into individual assemblies

The principles governing the sequence in which the various tasks arecarried out are determined by component delivery times Experienceshows that castings take a long time to deliver, particularly i they arebought out and if there isthe added complication of obtaining quotatio s

from a number of firms A similar situation may arise with large forgings

such as crankshafts It is therefore necessary to take care to ensure thatparts of this nature are tackled first and designed to completion Theproduction shops of the designer's own firm will also need early informa-tion on materials, tools, gauges, jigs and fixtures, etc I may also benecessary to release suitable machine equipment and lab ur for production

purposes Consulation with the works on manufacturing facilites andwork preparatio is indispensable In economically run works ithas, after

all, lon been the practice to make use of planned work preparation in sofar as the subsidiary work necessary for the manufacture of an in ustrialproduct falls wihin the province of the works

By planning the execution of these preliminary tasks through the ing offices, the rapid fulfilment of an order can be supported most effect-ively and the smooth and trouble-free development of all the subsidiarywork involved guaranteed.

draw-In the most general case, therefore, the designer's work-plan includesthe following sections:

1 Exact determination ofthe customer's requirements or of the problem posed

2 Checkin the order asto feasibil y of carrying it out with the firm'sown resources

3 Supplyof all data, preliminary work, etc needed for carryin the design through

4 Ascer ining possible solutions and choosing the best solution

5 Meth dical working out ofthe overall design

6 Split ng up ofthe overall design into groups

7 Detail design, ta ng priorities into account

8 Consultation with works on production planning

9 Production design of assemblies and components

1 Consultation withworks, and posibly wih customer also, regarding suggestionsfor modifictions

11.Production of an necessary works drawings

12 Inspection of the finished item and/or carrying out of bench testing and evtion oftest reults

alua-13 Obtainin ofcustomer's verdict on behaviour inservice and poss le suggestionsfor improvements

Since it is only possible to discuss below the purely design measures, it

is only points 1,4,5,9, and 11which are of concern to the student designer.What are the factors influencing design?

A detail designer will have lit e difficulty in allowing for design factors,because he will be given so many data and general principles that he will beable to solve his task without having any insight into the factors determin-ing the system asa whole Naturally in the course of time he will becomeacquainted with new aspects of engineering, so that he will graduallybecome familiar with the whole range of the designer's work However,the path from bein a detail designer working to instructions to being anindependent designer is a very long one, and only young people who areaspiring and persevering succeed in traversing it

It is therefore necessary that gifted students should, even during theircollege days, be made familiar with the solving of design problems whichthey will not be dealing with in practice unti they become independentdesign engineers

When working through a design problem the beginner soon realizesthat, apart from taking into account all the customer's requirements, hemust also bear in mind a whole series of factors concerned with manu-facture These will arise in such abundance that he will not know how

or in what order he is tomaster them At the same time not all the ments can be taken into account in equal measure Often they are quite

require-contradictory According to A Erkens the art of the de s igner consi s ts

" in prolonged checki n g, po n de r ing , and compromising on r equirements which a re often quite contradictory until t here a ppears-as the end pro -

d ct of numero u s assoc i ations o f i d eas, of a netwo r k of ideas-the design."

Si n ce the factors involve d in new tasks may arise continua ll y in f r esh forms , it is easily unde r standab l e why eng ine er s l ike Reul e u x a nd Bach should s p eak of a n infinit y of requi r ement s If the c o mmon fe a tures of many such f actors are grouped together under collective headings s uch as ,

say , m a nufacturi n g methods or prope r ties of m a terials , then there result ,

as shown by C Yolk, a bo u t thirty such points which influence d es i g This in its e lf is a ve r y bi g s tep fo r war d , f o r t h e b eg i nne r c an now see whether or no t he has ove r looked one of th e i mpor t ant re q uirements The in f luencing f a ctors c a n b e classi f ied in v a r i ous w ays To gi v e the stude n t a quick sur v ey of them it is proposed to adopt the cl a ssif i c tion of

Dr Wogerbauer who divides them into :

I Tasks imposed d irectly by the cu stomer's r eq u irements

II Tasks imposed b y pr ob lems of manuf a ct u re in the shops

I T a s ks impo se d by req u i r m ents

Required action

Mechanical loading

Climatic influences

Chenlical liIluences

Mechanical environmental conditions

Economy of energy consumption

Servicelife

Design

MaterialCondition of material

Coatin materialMaterial avaiabi ty

Manufacturing methodAssembly methodLabour requiredMachine equipmentLimits and fitsQuality ofsurface finishJigs, fixtures and tools

Gauges andinspection facilitiesDelivery date

Cost ofmanufacture

Natonal standards, works standard itemsMaterial standards

Scrap utiization

Patents

Use ofexisting productsThe signi f ic a nce of i ndividual facto r s may ch a nge very greatly with dif - ferent tasks T he listing a b ove t he refor e does not im pl y any spec i f i c ran k ing.

H o w can one c lassify t h ese fa c t ors clearly?

T he indivi d a l f a cto r s do no t exis t n depen d ent l y of o ne another Th e y can therefore not b e t r e ted separate l y when solving a problem Even a

beginner engaged in solving the simplest of problems soon notices that thefactors which he has to take into account are all interdependent and that,indeed, several of them need to be considered simultaneously.

A distinction can be made between direct and indirect relationships ofthese factors; for example, the quantity required affects manufacturedirectly and design indirectly

If one investigates the mutual relationship of the various influencing

fa tors one finds that working principle, material, manufacture, and design

are involved in most relationships These four points therefore assume a

special significance They form group foci which make for much greater

clarity in the processing of desig work

These four group foci are listed below together with their influencing

Mechanical loadin

Quantity requiredDelivery dateMaterial avaiabilityScrap utilizationFreedom from noise

Manufacture

Mechanical environmental conditio s

Size

WeightStandard itemsExistn products

Appearanc

Handling

Maintenanc

OverhaulSurface finishFitness for shipment

Power required

These four group foci likewise stand inamutual relationship with each

other For example, desig affects material and working principle Thematerial can only be selected after taking working principle, design, andmanufacture into account

F i g 3.-S howing ho w wo r king pr i n cipl e , m ate ri a l m an u fa ctur e ,

design , a nd c o s t a r e inte r connec t e d

It will be seen, therefore, that design involves sortin out avery plicated set of relationships Thus it is not surprising that the first effect

com-of these observations on the beginner is very confusing and discouraging

Despite these complicated relationships between the design factors it is

possible to organize the procedure and thereby to simplify it very greatly

IV A PLANNED POLICY FOR THE DESIGNER

Experience teaches that in all branches of human activity, no matterwhether manual or intellectual work is involved, only a systematicallyplanned method of working can guarantee success in the shortest possibletime

It is possible, of course, to advance arguments against the systematicmethod There will be many, perhaps, who fear that a systematic workingplan might force the designer into a Procrustean bed from which he cannever escape Anyone who believes this overlooks the fact that all thosewho do successful work, whether in the physical or intellectual fields,make use of such methods in their work-methods which they use con-sciously to begin with during the learning stage and then unconsciously

as their mastery increases Nor does the designer become hampered in

his work, much le s intellectually ossified, b using" systematic rules"

When methodically planned thinking has become habit with him he will

be able to create all the more freely

The systematic working plan is indeed time-saving, but not in the sense

that one may regard design activity as piecework The deliberations whichnecessarily accompany any successful design work can certainly not beaccomplished in a fixed time in the way that is possible with a practisedmanual skill

Wehave seenthat themajority of the engineering factors can be accom

-modated in four groups The only question now isto determine the mostsatisfactory sequence for dealing with them Experience shows that the

following path is the most practical o e

First, s tudy the p roble m a n d p repare a fr ee h and sketc h or b a sic design

t o estab li sh the required princip l e of action; t h en se l ect the material, and

f inally carry out the design work with an eye to economy of manufa c ture

That, in very general terms, is the systematic working plan for the

designer It can be ilustrated diagrammaticaly on the lines of fig 4

,

F i g 4.-The s y s t e ma ti c workin g p la n

We will now proc ed, in the co rse of the pages which follow, to

discuss these factors in the same sequence

The overal working plan for the designer breaks d wn into the

following sections:

I Exact formulation ofthe problems and defining of allquestions relating thereto

Il, Seting out of all possible solutions capable of providing the action called for inIindiagrammatic form (basic design) and selection of the optimum solution

III Selection of the most suita e material

IV Consideration ofproductio engineering problems

V Deciding on the most appropriate form design

VI Ascerta ing overall cost

In its diagrammatc form the basic desig represents a frameworkwhich gives only a hint of the final form To arrive at a basic shape thedesigner must first make assumptions about the material and the method

of manufacture, in other words he must run through the thought sequence

material - 7manufacture - 7form

After he has decided the basic shape, the designer has an approximatepicture of the structure in front of him and can then proceed to a well-considered selection of the material This done, and having taken intoaccount all the economic factors for manufacture, he is also in a position

to undertake the form design

Fig 5.-The systematic working plan when o erall cost conditions

are not satisfied

Overall cost always decides the final form taken b the work Ifthecost aspect isunsatisfactory it will benecessary to re-examine the situation(SOt fig 5) in the sequence

material - 7 manufacture - 7 form - 7cost

Before a start can be made on the design solution of an engineerin

problem it is necessary to clarify as much as possible the vario s points

which are to be taken into accou t when dealing with an order

The types of problem to be solved

The demands which a customer may make can involve the followin

it is very important to have ac urate knowledge about the prioriy ran ing

of the individual requiements I will often be found that the customerhimself is still unclear about them It will therefore be of advantage forhim to meet a representative of the firm so that he can define his require-

ments as closely as possible and be informed about the practicability offulfilling them Often, however, it is only the designer who can make a

definite statement ab ut the extent to which the customer's requirementscan be met It is always ad antageo s to both par es to define therequiements as accurately as possible prior to starting work on the

solution

For this purpose there are vario s systematic evaluation plans which

c n be used Evaluation of the necessary requirements c n be carried out

on a points basis as folows

1 Requirements which must be unconditionally fulfilled

2 Requirements w ch must be fulfilled as completely as possible

even though the solution leads to a compromise

3 Requirements whose fulfilment can only be insisted on if such

4 Requirements which are unimportant and can beneglected

3points

2 points

1point

opoints

Here, as in many other q estions arising in engineering, a graphical

representation is preferable to a tab lar one, and this is therefore given

in the diagram (fig 6)

Naturally, too much must not be expected from the graphical presentation The scope of the problem to be solved will often be very large Theoperating conditions and performanc schedule for a locomotive occupy,

-for example, a wh le book For instances like this fg 6 is unsuiable.

But in many other instances, where the task is not so large, it brings the

desig er imporant advantages He is able to spot immediately the differ

-ence in priorities to be given to the various requirements of the cutomer

and, by drawing in the diagram lines for the solution reached, he will see

rig t away to what extent he has satisfied the requiements

The ideal would be to fulfil all requiements to the same extent, but

usualy it will be necessary to make do with a compromise It must be

insisted, however, that all requirements c rrying two and three points areachieved

Mechanical en vi nm ent a l cond i on

Clim a t c environmen tal con d i ti n

S i z , we ig ht

S e r v i ce l f e Energy co n s ump t io n

e t c.

Fig 6 - C h ara c te n s t ic graph indic a tin g p ri or i ty rankin g for a g i ven problem

We will examine below, in more detail, first of all the factors which in

general meet the customer's requirements

Func t ion - A spe ific fu ctio is required of every machine, every

appliance, and every simple machine component Depending on the

action of the particular design element, so the following different ty es offunction are distinguished:

mechanical, electric l, optical, thermal, magnetic, acoustic

Among these kinds of function it is really only the mechanical onewhich occurs on its own All other components without mechanical

function are also stressed mechanically in view of their mechanicalconstruction

It frequently happens that other functions come into play, as for

example with commutator bars These have the primary duty of acting

electrically Owin to the passage of curent, however, they heat up and

owing to centrifugal effects they are subjected to not inconsiderablemechanicaloadin , The fact sh uld be carefully noted that these are

actions which the customer does not want at al The customer wh

orders ~n electric motor isonly anxious to have electrical energy converted

into mechanical power at a given torque and speed in the most economicalmanner possible Apart from the specified functions, therefore, the designer

also has to take into account a number of others arising out of the design

The function called for by the customer is obtained by a meaningful

arrangement of various constructional elements Itis usually possible toobtain the same function in a variety of ways For example, if the pro lem

involves making a work-able reciprocate, then there are several solutionswhich can be adopted Itnow becomes the primary task of the designer

to find out these solutions and then to select the best one in a manner

which will be dealt with later

Mechanicalloading.-Apart from the loading imparted by the desiredaction, an engineering product is influenced mechanically by the place

where it is used These infuences are forces, knocks, vibration, speedsand accelerations brought about by the particular conditions of use Undertlus heading also belong all possibilities of damage arising from careless-

ness, such as jolts, allowing the product to drop, etc

information about mechanical loading of this kind It is therefore thedesigner's duty clearly to identify and define it If there is no empirical

information available he must provide himself with the necessary data forcalculation purposes by carrying out a theoretical examination or, ifnecessary, by experiments

Climatic and chemical infiuences - The immediate surroundings of the

place of use have a powerful influence on design The principal climatic

effects are of a thermal and chemical nature Depending on external

conditons, therefore, the engineering product must be resistant to largetemperature differences in summer and winter, to wide varations in

humidity, to the chemical effects of a variety of gases and vap urs, and

to the corrosive action of water or aqueous solutions of salts, acids, bases,electrolytic cell formation, etc These factors call for special attention

in the design and constructio of chemical plant

The mechanical, climatic, and chemical influences of the environment

naturally are closely related to the various modes of functioning as shown

Mechanical environmental conditions.-Under environmental co n ditions

are grouped all the customer's specifications relating to the observance ofspecific location limitations Such conditions can often cause the designer I

difficulty; for example, he may have to accommodate an overheadtravelling crane in a very restricted space or find room for a gearbox in avery cramped location Inthe automotive and aircraft fields considerations

of this kind frequently confront the designer

Size and weigh t -For e onomic reasons alone, every designer en

-deavours to keep the dimensions of the product he designs down to theminimum, even though no restrictions in this direction are wrtten intothe contract The demand that the amount of space occupied and the cost

of materials used shal be kept to the minimum assumes such fundamental

importance in design work that designers frequently see in these factorsalone a guarantee of a correct solution to the problem in hand

When, as in the automobile, aircraft, and shipbuilding industries, how

-ever, special rules are made regarding dimensions and weights, then the

designer must make still greater efforts to satisfy the demand for minimum

size and weight All the design factors concerned with achieving an

exceptionally lightweight design are grouped under the concept" liweight construction ", to be dealt with later At one time these principleswere considered of such importance in the training of designers that aseparate branch of study entitled" lightweight construction" was intro-duced in the engineering colleges

ght-Fit n ess for shipment - The form design of engineering products mustalso take account of the various methods of transportaton used Apartfrom fitness for shipment, the question of transportatio cost includingcustoms duties also plays a par Large and bulky items will be sub ivided

b the designer to permit shipment Even where small products are

conc rned, however, i may be necessary to consider fitness for trans

-portaton; instruments, for example, are often very susceptible to joltsand vibration They can be made transportable by arranging for thelocking or dismantling of certain components

Handling - The main point to consider inconnection with the han ling

of a product is what type of personnel-skilled or unskilled-will be

operating it Similarly, the mode of o eration also decisively infuencesthe form adopted for the controls and other devices used in handling theproduct The controls on a locomotive will certainly be designed on moremassive lnes than those of a heavy goods vehicle, and the latter in turn

wi look different from those of a smart motor car Many handles, levers,and hand wheels are standardized When free to decide the form of these

elements, the designer will be guided by the considerations discussed above

The psychological reaction of the customer must also be taken into account

Maintenance.-Maintenance implies attention to the tasks which have

to be performed to keep plant or equipment in running order It covers;

tasks such as cleaning, lubricatin , retightenin bolts, and changing worn

or defective parts To enable these operations to be carried out morequickly, the designer must arran e for easy access to the parts conc rned

and must limit the number of tools needed for maintenance purposes tothe minimum

Overhaul facilities.-As far as overhaul facilities are concerned, three

possible situatio s must be considered In the first place it may be found

that to repair a simple product is more expensive than to repla e the

complete unit In an instance like this it would bewrong practice to su

b-divide further for the sake of replacement When parts are subject to a

high rate of wear it is often advisable to design them with a view to

repla ement and to supply the customer with replacement parts which he

can fithimself Athird possibility is that specialized knowledge isneeded

to effect replacement or repair In an instance of this kind it will even benecessary to take steps to ensure that the customer does not interfere with

the product, but sends it in for repair to the firm that supplied i or to a

suitable repair firm

1

Ene gy consumption.-For financial reasons itwill be of special interest

to the customer that the product he is calling for should have the smallest

possible consumption of energy, that is to say that it should be as omical as possible As far as the desig er is concerned this requirement

econ-means that in formulating the design of the product he must find out all

the factors which have an important influence on the reduction of energy

consumption, so that he c n take them into account in his design Theeconomy of a product in regard to energ consumption is a reliablecriterio of the quality that goes into its manufacture and is one of the

factors determining product competitveness with earlier and les advancedversions

Service li e.-Every purchaser of an engineering item is interested in

securing the longest possible service life from it It therefore remains an

imp rtant prnciple for the designer, even if the customer makes no specialstipulations in this direction, to ensure by appropriate dimensioning of

parts, correct choice of material and attention toany other points, that the

product will stay in service for the maximum length of time No doubt

the ideal situation would be for all the design elements to possess anequally lon life span It usualy happens, however, that certain parts have

a shorter life than the unit as a whole owing to mechanic l, thermal or

chemical effe ts If a prolonged breakdown is to be avoided in an instance

such as this it is essential that the we rng pars sh uld be designed for

rapid replacement

Rel abi l ity - De p en d abil y is a quality held in high esteem by everypurchaser of an engineering product which is required to operate co -tinuo sly Trouble-ree performance at a specified rating or capacity

depends primarily on the reliability and certainty of functioning of all the

design elements involved

From this there devolves o the designer the responsible task of

constanty examining even the smallest details of ills work as itprogresses

to discover what the individual components are su jected to in the way

of harmful influences, possible overloading, we r effects or other troubles,and what repercussions these factors have on product reliability

Operat ng cost.-Quite closely tied up with the question of energy

co sumption isthe factor of operating cost For the most part this finds

its expression in the efficiency of the item concerned The designer must

therefore take into account all factors which have a bearing on efficiency

Unsatisfactory handling and operation in service can cause wear and

le kage leading to loss of lubric ing oil, cooling water, fuel, vapour, gas,

etc., which will increase the cost of operation to amarked extent In the

customer's own interest, therefore, the supplying firm willprovide him with:

Operating inst r uctions - The purpose of these is to give the customer

informato on operatio and on re ognizing faults promptly and rect

ify-ing them At the same time operatn instructions give the supplier a

certain amount of protection against unfounded complaints and supporthim in disputes

Appearance.-The saying" everything which fits its purpose looks

right" apples in general to the desig er But there are man industrial

products which the public wants to see designed wih aclean and smooth

external shape Where machine tools are concerned, great imp rtance is

attached nowadays to tils kind of appearance Since external appearance

has little influenc on internal co struction in tills instance, the designer

is able to me t the customer's taste for the contemporary wih ut difficulty

Freedom from noise.-A machine which works noisily will in the lo g

run be unacceptable to the owner himself Still less is it permissible to

annoy the surrounding neighbourhood with such a machirie, for such

annoyance would very soon lead to legal action For the designer there

are various ways of eliminating or reducing undesirable acoustic effects

A noisy machine must be mounted in a manner providing acoustic

insulation, and a change of site often helps to solve the problem Treat

ment on a theoretical basis isusualy inconclusive owing to complications

introduced by surroundin structures; here only experment c n providethe answer

De l ivery date - Eve r order made is subject to an agreed delivery date

Sometimes the date is laid down b the customer, but usually it is the

result of joint negotiation A delivery date must never be fixed without

prior discussion with the drawing office and works, particularly where new

desig s are co cerned When large orders are involved, compliance withdelivery dates is often enforced by agreed penalty clauses

Quantity r quired.-Information on the quantity required will of course

always be provided It is of great importance in settling questio s of

material and production method, and in this way it sig ificantly affectsthe design itself For example, if the quantity required is small, it will benecessary to consider whether c sting is still economical or whether itwould be better to go over to welding or forging

Overall cost is ofthe greatest interest to the customer. It also influences

the designer's work to the extent that he must endeavour to choose his

materal an design his product on economic lines, so that a competitive

overall price will result

Types of problem to be solved.- Two classes of problems are to be

dis-tinguished, depending on whether they originate from the customer or from

the desig er's own works, as shown by the following list

{Ready-made product

Read -made product wih modifications

C t ' d Complaints about machines previo sly supplied

usornersor ers Repairs

New design

Improvement{Further developmentWorks' orders New design

Invention

, Customer's orde - The best policy is for the customer first to informhimself adequately throug ad ertisements and recommendations of the

existence of a firm which appears likely to meet his requirements By

making adirect approach to the firm concerned or to one of its represatives, he should then obtain expert advice for the purpose of exactlyformulating and defining his order Descriptive publications, leaflets, and

ent-c talogues should not only serve advertising purposes but should alsocontain all data of importance to the customer, such as principal dimen-

sions, weights, guaranteed values, graphs where applicable, and simple

explanatory sectio al drawings A properly informed customer will naturally be able to express his requirements in such a way that there will be

-no need for a lot of discussion with the drawing office

The majority of orders will concern items which are in regular

produc-ton but require slight modification in layout, or the additio of certain

attachments to meet the customer's special requirements Modification

work ofthis kind forms the principal actvity of the design offce in a lot

of instances The work involved is mostly adaptive design

Apart from desig work of this kind, the customer may present parts

to be replaced, repairs, or suggestions for improvements This ap lies

particularly where insufficiently tried new designs are inv lved Adaptive

design of this kind, however, calls for great care in the interest of preservingthe firm's good reputation The primary task ofthe designer in this situa-tion is to examine the true causes of the complaint very carefully, so that

the defects which have become apparent can be eliminated in future bappropriate modification and improvement

Work which calls for the maximum of design capability isthe solutio

of new problems presented by the customer Very often it is only b

experiment and theoretical investigation that the basis can be created for

resolving the design side of a problem for which there is no existing

solution

Wo r ks' o rd e r -A p rt from customers' orders, every firm always has

designin to do on its own a count Part of this work is concerned wihimprovements suggested by experience gained in after-sales servicing, and

part of it is concerned with development arising from stu y by the firm

of its own products

A special class of order re ching the drawing of ce is the kind whicharises from efforts made by the firm on the basis of a careful stu y of the

market to create by its own efforts new designs or improvements in design

which, ba ked by patent protectio , will constitute a marked advance in

the field of engineering concerned In work ofthis nature the designer has

to be specially mindful of economic principles, so as to create from the

start aproduct which not only represents a significant improvement in the

range ofpossible solutions, but also offers the chance of gaining an effective

lead on competitive pro ucts b virtue of the price at which it is offered to

the market In this kin of design work the policy should be to create a

product which, b means of interchangeable and adjustable parts, by the

fit ng of extras an special features, and by the pro ision of extension

facilities, is able to ofer the maximum of adaptabiity

Exercise problems

Study of the design problem is part of the trammg of the young

desig er, and the problem must therefore be defined with sufficient detailand precision to avoid any need for further queries To the best of myknowledge the colleges have not so far adopted exercises of this kind Theproblems set are mostly so incomplete that the student has a great deal of

latitude for making his own assumptions, and, if he is of a critical turn ofmind, he will continually be asking his teacher questions