Earnest T. Childs.

In the first talk on Mechanical Drawing under the heading of " Instruments, Their Use and Care," a brief description was given of one class of scale, commonly known as the Architect's scale. As therein stated, the common scales have subdivisions which are divided to a scale of \" to 1' up to 3" to 1'. This class of scale is used most commonly on architectural and machine drawing. There is another style of scale used by civil engineers which is entirely different from the architect's scale, which is generally called the Engineer's scale. The scale is divided into inches, and each inch is divided into a certain number of parts, from 10 to 100. That is, in a triangular scale having six edges, the common subdivisions will be 10, 20, 30, 40, 50 and 100 to the inch. To make the outfit complete another scale is necessary, giving 60, 70 and 80 divisions to the inch, and perhaps repeating some of those on the first scale. Some draughtsmen prefer to have a collection of flat scales instead of a triangular scale. If expense is not to be considered this is a good idea, as it lessens the liability to error, as the draughtsman uses only the scale needed for the drawing on which he is working.

While the use of scales is familiar to all •draughtsmen and to all mechanics who are accustomed to read drawings, there are many who have only the faintest idea of the use of scales as applied to drawing work, or as applied to •everyday work of any sort. The primary function of the draughtsman's scale is to produce on a small area a representation having,the exact proportion of a much larger object or area.

For instance, suppose that a man has a tract of land, and wishes to build on it a house of a certain size. He also wishes to know the most satisfactory arrangement or location for the house on the land. Also suppose the lot to be irregular, and not quite level. He may be able to take a tape and measure off the ground, locating the corners of his house by stakes; but when this is done he cannot take a comprehensive view of the situation and be sure that he has the best location. For illustration, assume the lot to be 100' deep, 60' wide at the front and 50' wide at the back ; and the house to be 25' by 40'. A man standing in front and looking at four stakes cannot accurately judge the situation. By drawing a plan of the land, on a scale of 8' or 10' to 1", he can draw in his house plan to the same scale, and readily determine just how much room he has to spare, and just where he wants the house located, to best utilize the spare land.

The same principle applies to larger work. A large group of buildings may be laid out on a 24" by 36" drawing board so that the eye can grasp the association of the various buildings, even though they cover several acres. Should the attempt be made to study out the arrangement by staking off the ground, nothing but confusion could result. A drawing of this type may be made to a very small scale, perhaps 50' to the inch; but since it enables the eye to grasp the entire situation, it is better and more comprehensive than if it were drawn four times the size.

This illustrates the use of the scale on preliminary work' where it is necessary to determine the most desirable location. After this preliminary work has been settled, it becomes necessary to prepare details for the construction. Here, for the sake of accuracy, it is necessary to use a relatively larger scale. Building plans are usually drawn on a scale of 1/4" to 1'; that is, 1' on the drawing equals 48' in the building. A building 50' by 100' may be shown on a plan 15" by 30", and the arrangements of partitions, doors, windows and equipment may be predetermined, thus preventing mistakes and conflictions. Small details of construction are often worked out on quarter-size, half-size, or even full-size detail sheets, for the sake of greater accuracy.

This illustrates the relation between the draughtsman's scale and the building trade, the scale being a very important factor in the design and erection of the building. Too little attention is given to the importance of the scale, and few who use them continually, realize their importance.

The scale, like the pencil and triangle, is part of the draughtsman's equipment, and that is all the thought given to it.

On machine drawing the scale is equally invaluable. While a large amount of work has to be laid out to full scale, by far the larger part is drawn to scale varying from 1/2" to 1' up to 3" to 1', the latter being quarter size. By means of the scale the relative proportions of the machine may be shown, and the eye can detect at a glance any inaccuracies which might be overlooked until the machine was about complete, or if the scale drawing had not first been made. It is necessary to learn how to use a scale accurately, as a scale drawing should be correct in every detail, even though figures are given for all important dimensions.

Thus it is evident that the scale is one of the draughtsman's most important instruments, as by its use he is enabled to see comprehensively what otherwise would be absolutely impossible.