W.S. Graff Baker, Esq., A.C.G.I., B.SC., M.INST.T., M.INST.L.E.
Chief Mechanical Engineer (Railways) London Passenger Transport Board
and President of The Locomotive & Carriage Institution
I want to talk to evening about a subject which nobody can teach; about something that is in all of us which can be developed; about something which is essential in engineering. I refer to the question of design. I do not want to talk about stresses in materials, volts and amperes, or pounds per square inch, hut rather about the form and shape of things and their relation to their purposes. I will assume that in the course of your experience or studies you have learnt the whole of the theory of structures and machines and that you know how to make the various parts, but this knowledge alone will not produce good design. To take an analogy, the artist must know good deal about anatomy before he can properly draw pictures of people or animals, but knowledge of anatomy is not likely by itself to give him a sense of composition or to result in drawings of beauty. Take, too, the question of architecture. It is quite easy for an architect to construct a building which will not fall down, provided he knows something about the principles of mechanics and the strength of materials, but it is rather exceptional to find a building which pleases and satisfies the eye, and relatively exceptional, too, to find a building which is functionally satisfactory in its arrangement.
What can be learned by study or practical experience is the anatomy of engineering and will not relate to the appearance or even, in fact, to the practicability of a design. I must insist that engineering design is an art just as much as is the work of a painter or an architect.
I have already said that this question of form in design lies within us all, hut it is a latent gift which requires development. It requires more than that, it requires a certain wish to develop it, and, frankly, it makes engineering design very much more difficult. It is easy enough to produce a machine that will work. It is not easy to design a machine that also looks well. One aspect of the question is that of simplicity. It can be said without any possibility of contradiction that if a machine is complicated in proportion to its function it is wrong; that is to say, that nothing but the utmost simplicity for a given function is right. It is no use expecting an automatic printing-
Then in the question of simplicity in design there is the influence of the T –square -
Then there is the question of not being hidebound on principle. Because a certain part can best be made in a certain way is not by any means an indication that that method is suitable throughout the design. Taking, for example, roller hearings for axle boxes, these are common practice today and for various reasons. They are not adopted necessarily to reduce friction. After all, there is no finer hearing than an oil-
The effect of welding on the construction of rolling stuck is very marked. It results in a lighter and more rigid construction, but it has the not inconsiderable disadvantage that it is much slower in construction than the old method of riveting. It is true that the riveted construction means that all the pieces have to have a large number of holes drilled to take the rivets, but on relatively small parts of the underframe this is done in a shop specially arranged for the purpose, and not much floor space is occupied until the frame begins to be assembled, which by riveting is done comparatively quickly. With a welded underframe the whole of the floor space occupied by the frame is occupied the whole of the time the welding is in progress, and the welding of a large frame is a matter which has to be dealt with piece by piece to avoid distortion of the whole. As a result, when a considerable number of cars require to be produced, it is found best not to weld the whole frame, but to rivet together parts of a reasonable size, which have been previously constructed by welding. This, again, shows that it is necessary sometimes two adopt two mutually supporting principles rather than to ask either principle to carry the whole weight.
The aspects of the subject of design are innumerable and the methods of dealing with the problem are almost equally varied. There is the trick, if you like to call it so, of turning a design inside out. If a design is unsatisfactory, this is one of the most certain ways of attack and the result is commonly right. As a case in point, I could cite something of my own experience, that of the design of a tripcock for a train .A tripcock is a valve, which is opened by an attachment fixed at the signal, so that if the train over-
The next slide shows you an example of inverting design in cars. With the introduction of sliding doors in saloon type cars it was found necessary to provide draught screens each side of the doorways to protect the passengers in the seats from the draughts. from the open doors. In view of the large doorway opening that was cut, particularly in tube cars, it was found desirable that the draught screen should form part of the basic structure of the car in order to reinforce the structure. To this end, as you will see from the slide, it was built up as a steel framed panel with windows. To the front of the frame was secured a grab-
To take another case in car design, it has until recently been the practice to fit a footboard along the sides of those cars on the London Transport services which do not run in the tubes. The reason for this footboard is to provide a means of preventing accidents due to passengers getting their feet down between the car side and the platform, reasons of clearance rendering it necessary that the car should not be of sufficient width all the way up to prevent this difficulty. It is only practicable to have a projecting piece at the low level. Such a footboard tends to collect dirt and makes the car more difficult to clean. Recent cars for this service have been constructed with the sides swept out in a curve at the lower region to the same point as the outer edge of the old footboard. This gives a better appearance to the car and provides for the necessary functional requirements of operation, while leaving a continuous surface which not only does not get so dirty but is easier to clean.
On the electrical side, too, simplification can he made on the basis of practical requirements. For example, it has been customary to fit hand-
Careful examination of the functions of wiring generally has led to certain changes. For a long time it was customary to run positive and negative wires in separate conduits on rolling stock having an insulated return. Systems of this kind are subject to the circumstance that, in the event of one pole grounding, there is not a short circuit created between the poles, as the current from the ground has to get back to the other pole by the insulation resistance of that other pole. This means to say that the current is limited by the insulation resistance of the whole of the other pole throughout the system to a figure, which, while not constituting a short circuit, will create a very destructive arc. It therefore appeared desirable to change the system by which wires were run in separate conduits and arrange for wires of a given circuit on opposite polarity to run in the same conduit, so that a ground would develop as quickly as possible into a short circuit and blow the fuses, thus isolating the fault.
The examples that I have cited of modifications, improvements and simplification in design are all drawn from my own practice and experience. If I might cite one simple thing outside my own experience, I would refer you to the design of driving mirrors for motorcars. Generally speaking, these are a very crude job. I have slides showing what I would regard as an example of good design in this connection, and what I would regard as bad design.
In the matter of design there is always the question of considering whether a thing should he made adjustable or not. Generally speaking, I am averse to making anything adjustable if it can he avoided. Adjustments are almost inevitably made by screws, and, in the nature of things, screws used for adjustment cannot be properly locked against working loose. The ordinary principle of a lock nut or a setscrew is simple and cheap, but mostly unsatisfactory. It is far better to design so that adjustments can be avoided altogether, or, if they have to he made, to arrange for them to be made by inserting shims or slim pieces of metal between the parts that need taking up for, say, wear.
The fastening of things together is another difficult matter. Where things require to be permanently fastened together, it is well to consider whether the apparatus could not be made in one piece; next, whether the parts could be welded together; next, whether they could be riveted together; and, finally, whether it is essential for them to be bolted together or fastened with screws. Set-
I see I am getting down to details, and this is a thing I wanted to avoid. I want rather to keep to main principles.
A vast deal of work is done in making drawings of things that are unduly costly when it comes to manufacture or maintenance. Many draughtsmen appear to be satisfied when they have made a drawing of something that will work. This is underrating the object of making a drawing. Perhaps I should have used the word ‘design’ rather than the word ‘ drawing’. A designer should consider these points:
1. Will it work?
2. Is it as simple as possible?
3. Could it easily be maintained in service?
4. Can it be manufactured?
5. Does it look well?
If these points have been taken care of in the design there is little doubt that everyone will be satisfied. If any one of them is omitted, the design is in fact poor, perhaps useless. A drawing is commonly a picture of one of a large quantity of things to be made. Generally speaking, it would pay to spend very much longer on the design on the drawing board than appears to be spent usually, and not only to spend more time, but more thought and more care and more energy in insisting on getting the right answer. Once a drawing is made, the articles are many and may last for years. A drawing is perhaps made in ten hours; each of the articles it represents may take, say, fifty hours to make and last fifty years. The draughtsman sees the thing once and never again, but someone has to look at, live with, and maintain the finished articles through the whole of their life. It does not do, even from a material point of view, to hurry or skimp drawing office and design work, while from aesthetic point of view it is invariably a tragedy.
All the examples I have given you indicate quite clearly, I think, the kind of lines on which I feel that engineering design should be studied. You cannot go wrong if you aim at the utmost simplicity, and if you design with a view to making an article that is not only finished but also looks finished, and a complete whole and not made up of little hits stuck on one another as if by a series of afterthoughts. Do not he in a hurry to adopt your first thoughts -