Introduction

It is perhaps significant that the use of 'drawings' for communication preceded the development of 'writing' by tens of thousands of years. This is not really that surprising, as a single sketch can convey data that might need hundreds of words -Fig.1. Furthermore, a well-executed drawing is far more precise than words; try describing a 3-throw crankshaft in words alone with sufficient detail to enable it to be manufactured. The use of drawing for such technical matters is at least 4,000 years old, though chiefly used in those days for architectural constructions and, perhaps, shipbuilding. Avery significant fact about such drawings, which have survived from hose early days, is that they can readily be understood - even though, in some cases, the associated written language has yet to be deciphered.

Technical drawing, as we understand it is, however, of relatively recent date, and the type of drawing we use today very recent indeed. Fig.2 shows a working drawing by Agricola (1556) describing the manufacture of a large bellows for supplying air to a smelting furnace. You will see that it is entirely pictorial in character. The complete bellows is shown at the bottom, and its components are spread over the rest of the sheet. (The original drawing would have been about 10 x 16

Fig.1 How James Nasmyth ordered dinner at a Swedish inn in 1842 (Smiles' "Life of Nasmyth")

A. Upper bellows board

B. Lower bellows board

C. The two pieces of wood of which each consists

D. Posterior arched part of each

E. Tapered front part of each

F. Pieces of Linden wood

G. Aperture in the upper board

I. Little mouldings of wood K. Handle

L. Cleat on the outside. The Cleat inside I am not able to depict

M. Interior of the lower bellows-board N. Part of the Head 0. Air hole P. Supporting bar Q. Flap R. Hide S. Thong

T. Exterior of the lower board V. Staple X. Ring Y.Bow

Z Its long pieces

AA. Back piece of the Bow SB. The bowed ends CC. Crossbar distending the Bow

DD. The two little pieces EE. Hide FF. Nail

GG. Horn of the Nail HH. A Screw II. Long Thong KK. Head LL. Its lower board MM. Its upper board WW. Nozzle

00. The whole of the lower

Bellows-board

PP. The two exterior plates

QQ. Their curved piece

RR. Middle plate of the Head

SS. The two outer plates of the upper Bellows-board

TT. Its middle plate

W. LittleAxle

XX. The whole Bellows

Fig. 2 "working" drawing for a smelting furnace bellows, 1556. Though not all to the same scale the parts are all in proportion. Leading dimmensions were given in text.

Fig. 2 "working" drawing for a smelting furnace bellows, 1556. Though not all to the same scale the parts are all in proportion. Leading dimmensions were given in text.

Fig.3 Working drawing of a grindstone, 1748. The parts are to uniform scale, shown at the bottom. Both oblique and "orthographic" systems have been used. (Plumier -"L'Art de Tourner")

inches tall.) There are no dimensions nor any attempt at a common scale - see the nail at FF, just above the workman, and the basket of nails just below. However, each view is in proportion and the actual dimensions of some parts are given in the text of the book (De Re Metallica) so that the craftsmen of the time would have no difficulty in building such a device. I quote an example where the width of the bellows is given as "3 feet. 2 palms and 3 digits wide" - units which were then as precise as our metres and millimetres.

Fig.3 is taken from L'Abbe Plumier's book on turning lathes, dated about 1749. It shows the parts and assembly of a

Fig.4 An early drawing from "the age of steam". Note the scale. (Farey - "A Treatise on the Steam Engine, 1827")

grindstone. Pictorial representation is still used, but the important parts are all shown both pictorially and in orthographic ('true drawing') views. All parts are to the same scale, and there is a scale of 'pouees' -French 'inches' - at the foot of the drawing. Again, there is further detail in the text of the book. (Incidentally, this explains the apparently redundant detail in the lower right-hand corner an addition to allow the wheel to be worked by treadle.)

It is important to understand how a craftsman making the devices worked in those days and, indeed, right up to the 12th century. He would most certainly not use the book, or a drawing, in the workshop, still less in the forest as seen in Fig. 2. If just one bellows or grindstone was required he would note the major dimensions, possibly scribe an outline on a piece of board for each part, and make each to fit. If the bellows was the odd digit larger or smaller this did not matter provided all the rest was in tune. If more than one object was required (e.g. wheelbarrows as shown in another of Agricola's drawings) he would make one first and check that it served its office. This would then be taken to pieces and each part of this prototype would be used as a pattern so that all future barrows would be almost identical. Hence the origin of the use of the word 'off to denote quantity. 'Three off' meant make three parts taken off that pattern or template.

It was not until the development of the steam engine that what we should recognise as engineering drawings made their appearance. Fig. 4 is a drawing by Fary (1827) of one of Smeaton's Newcomen-type engines (1772) which is typical of these early days. It needed the invention of the blue print process in 1840 to allow copies of drawings to be distributed so that all the craftsmen concerned could work to identical drawings. Engineering drawings then became a truly international language, and it is now possible for workmen in any part of the world to be supplied with the same detail drawing.

Section 1

Was this article helpful?

0 0
How To Have A Perfect Boating Experience

How To Have A Perfect Boating Experience

Lets start by identifying what exactly certain boats are. Sometimes the terminology can get lost on beginners, so well look at some of the most common boats and what theyre called. These boats are exactly what the name implies. They are meant to be used for fishing. Most fishing boats are powered by outboard motors, and many also have a trolling motor mounted on the bow. Bass boats can be made of aluminium or fibreglass.

Get My Free Ebook


Post a comment