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will be readily seen that these three views give every dimension that would be required in making the given object from drawings, that is, height, width and thickness.
In fact, the front and top views without the side view give all that is required.
In mechanical drawing, when the object is complicated, it often happens that three views must be given to thoroughly depict the work, but in plumbing, usually only the top view, or plan, and one elevation is required.
At this point it is well to state that many of our readers will no doubt have difficulty in thoroughly understanding what we have written on projection. To these we would say that even though at the outset the subject is not clear, it will become plainer as the subject advances, and that it should not be an obstacle to going on, for we shall soon deal with the subject in a way that will appeal to the plumber from a practical and not from a technical standpoint, such as the opening of a matter of this kind must be.
N obtaining the views of an object,
that is, the projections, as they are called in mechanical drawing, such
as Fig. 7 shows in the preceding article, it is not necessary that the object be placed in any particular position when the views are taken. In ninety-nine cases out of a hundred, however, the object is supposed to be placed in the position from which the views can be most easily obtained, that is, directly facing the observer.
Suppose we consider, for instance, a short length of steel rod having six faces.
If the piece is placed so that it is squarely in front of the person making the drawing, with a face fully exposed, the front and top views would be such as
Fig. 8 shows, but if placed in some odd position, such views as Fig. 9 shows will have to be made.
Either set of views shows the dimensions of the object equally well, but Fig. 8 is preferable, because simpler. It will be noticed that in which ever position the object is placed, the two views or more that are taken must be consistent. It would not do to combine the front view of Fig. 8 with the top view of Fig. 9.
With these explanations we shall leave the subject of projection as far as its technical points are concerned, though we may have to allude to it occasionally. In writing this series, we thoroughly appreciate the fact that very few of our readers in all probability, have ever taken up the
subject of projection, that is, the making of working drawings, and we do not to scare
readers into the thought that they have got to grind away at that part of the work before being able to take up the real plumbing drawing.
It does not require any book knowledge to do the work either. A knowledge of plumbing, an eye to proportion, and some little skill are all that is required. The two latter qualifications naturally can be obtained only by practice, and to this end we would earnestly advise our
subject, such work appears very inferior.
It is often seen, however, hardly a sketch made at examinations, indeed, that does not testify to the work. To thoroughly illustrate our meaning, we show in Fig. 10 a combination of perspective and mechanical drawing, and in Fig. 11 the same work in which nothing but mechanical drawing is to be found.
We give also in Fig. 12 à drawing which is entirely perspective.
Comparing Figs. 11 and 12, either one is correct, and shows the work in proper manner. However, perspective,
Figure 12—An Illustration of Perspective Drawing readers to practice making drawings as such as shown in Fig. 12, is much more we proceed with the subject, and after difficult drawing than the plain mechanihaving made them, to compare the same cal drawing of Fig. 11. with our sketches, and apply the criti- Therefore it would seem to the writer cisms, which we shall make from time that as Fig. 11 illustrates a style of work to time.
which is entirely acceptable in showing In starting into the subject of plumb- all that is necessary to be known about ing drawing, we wish to emphasize a the work, it should be chosen in prefer. fact which we have already tried to ence to perspective drawing, and accord. make clear, and that is that perspec- ingly hereafter in this series we shall tive drawings should never be com- confine themselves almost entirely to the bined with mechanical drawing, for to plain drawings. those that have any knowledge of the We may add that it is not once in a
hundred times that perspective drawing is required, though occasionally it is very valuable in showing work in its proper shape.
In Fig. 10, which illustrates the same piece of work as the other two sketches, we find the two classes of drawing combined, and the effect is poor.
It will be noticed that while a plain, mechanical view is given of the tub, the lavatory is shown entirely in perspective, and the water closet partly so.
The latter shows especially poor taste. A glance at the water closet will show that while the main part of the bowl is shown plain, the circular rim is shown in its perspective appearance instead of the manner shown in Fig. 11. If the upper part of the bowl is in perspective, the whole drawing should be, as shown in Fig. 12.
This error is met with time and time again. As we have stated while considering the subject of projection, in mechanical drawing a view may be taken looking directly down onto the object, and another view may be taken by looking directly at the front of it, but in this branch of drawing, the two
views must never be run together, as they must have been to give the view of the water closet shown in Fig. 10. Another point to be observed in connection with the work shown in Fig. 10 is that, if the drawing is designed to show the work in perspective, to be consistent, the piping should be shown in perspective just as much as the lavatory is, and after the style in which the piping in Fig. 12 is drawn.
A fixture should never be drawn in perspective without making all the work connected with it to agree.
For instance, the trap, waste, and back air for the lavatory are shown plain, which is inconsistent with the appearance of the fixture itself. The back air pipe running straight up from the crown of the pipe looks as if it must break through the bowl and marble slab, while the lines which are dotted show that this pipe in reality runs behind the marble back.
It should be noted that when lines of pipe or, in fact, any part of the work is hidden behind anything it is customary to dot the lines instead of making them full. Thus in Fig. 12 the pipe that runs under the floor is shown dotted.