Referring now to Fig. 128, it is most likely that the front elevation would be next drawn after the plan. For this purpose the plan should be so placed upon the board that the part representing the front should be turned toward the bottom of the board, in which position it appears to be turned toward the observer. Place the T-square so that the blade lies vertically upon the board - that is, crossing it from front to back - and bringing it to the different angles or points of the front side of the plan, draw a line vertically from each, through that portion of space upon the paper allotted to the elevation, all as shown by the dotted lines. Thus each point of the elevation comes directly over the point which represents it in the plan, and the horizontal distance across any part of the new elevation thus becomes exactly the same as that of the plan. The question of bights is here a matter of design and is governed by specifications supplemented by the designer's judgment. With the plan and the front elevation complete the drawing of any other elevations or sections is entirely a matter of projection, except as new features might occur in those views which would not appear in either of the views already drawn.

Fig. 127.   Elevation Projected from Section.

Fig. 127. - Elevation Projected from Section.

If an elevation of the right side is about to be constructed, lines would be projected horizontally to the right from every point in the front elevation of the object which would be visible when seen from the right side, thus locating all the (lights in the new view. As the horizontal distances in this view must agree with distances from front to back on the plan, they may best be obtained by turning the plan (or so much of it as nec-cssary to this view) one-quarter around to the right, so that the side of which the new elevation is to be drawn will be toward the bottom or near aide of the board, as shown at G: alter which lines may be projected with the T-square from the points of the plan into the elevation, intersecting with corresponding lines, as shown. The same result may be accomplished by projecting the lines to the right from the sale of the plan, as shown in the top view, until they reach any line parallel to the side, as H I. From this line they ma\ be carried around a quarter circle from any convenient center, as N, arriving at a horizontal line, N M, and thence dropped downward, intersecting as before.

Fig. 128.   Principles of Orthographic Projection Illustrated.

Fig. 128. - Principles of Orthographic Projection Illustrated.

Drawing. ft will thus be seen that the elevation of the right hand side of any object comes naturally at the right of the front elevation, and the left side elevation, at its left. This idea is best illustrated by supposing that the object in question be placed in a glass box of the dimensions of the base H I J K of the top view, and that the elevation of each side of the object be projected upon the adjacent parallel side of the box at right angles to the same, and that afterward all the sides (supposing them to be hinged at the corners) be opened out into one plane, as shown by K L, H O and O P (the lop face of the box being opened upward), thus displaying all the views in one plane as represented by Fig. 128.

Fig. 129.   Vertical Sections Derived from Fig. 128.

Fig. 129. - Vertical Sections Derived from Fig. 128.

This idea should not be carried so far as to open the bottom face of the box downward, because this would produce a plan as seen from below, which is never done except in the case of a design of a ceiling or soffit, when it should be spoken of as an inverted plan.

In Fig. 120 the transverse section is shown at the right of the longitudinal section, because the view in it is from the right, or in the direction of the arrow in the longitudinal section, showing what would be seen if the house were cut in two on the line A B of the plan and the right hand portion removed. The longitudinal section is for the same reason placed at the left of the transverse section - that is. it is a view from the left of the house when placed in the position shown by the transverse section. From the foregoing it is to be understood, therefore, that when a view appears to the right of another it is supposed to show what would be seen when the object is viewed from the right hand end or side of what is shown in the other, the other (or front) view being at the same time a view of the left side of what is shown by the right side elevation.

In this class of drawings various kinds of lines are used, each of which possesses a certain significance.

The general outlines of the different views should be firm and strong enough to be distinctly visible, without being so broad as to leave any doubt as to the exact dimensions of the part shown when the rule is applied for purposes of measurement.

It is not always necessary that all the lines of projection should be shown. When shown they may appear as the finest possible continuous lines, or as dotted lines such as are shown in Figs. 127, 128 and 129. Lines used in carrying points from a profile to a miter line, or from one line to another for any purpose, are really lines of projection, and for the pattern draftsman's purposes it may be said that the finer they are drawn the greater the accuracy obtained (see Chapter H under the head of Lead Pencils).

Dotted lines are also used to represent portions which are out of sight - that is, back of or underneath the other parts which constitute the view under consideration, but which it is necessary to show, as, for instance, a portion of the chimney in longitudinal section Fig. 129 and points D and F in the profile of the mold in Fig. 127.