Carpentry for Boys Part 7

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112. _Scarfing._--Cutting timber at an angle along its length, as the line A. Scarfing joints are variously made. The overlapping joints may be straight or recessed and provided with a key block B. When fitted together they are securely held by plates and bolts.

113. _Scotia Molding._--A sunken molding in the base of a pillar, so called from the dark shadow which it casts.

114. _Sill._--In carpentry the base piece, or pieces, A, on which the posts of a structure are set.

115. _Skew-Back._--The course of masonry, such as a stone, A, with an inclined face, which forms the abutment for the voussoirs, B, or wedge-shaped stones comprising the arch.

116. _Spandrel._--The irregular, triangular s.p.a.ce, A, between the curve of an arch and the enclosing right angle.

117. _Strut._--In general, any piece of a frame, such as a timber A, or a brace B, which resists pressure or thrust in the direction of its length.

[Ill.u.s.tration: _Fig. 118.-Fig. 123._]

118. _Stud, Studding._--The vertical timber or scantling, A, which is one of the small uprights of a building to which the boarding or plastering lath are nailed.

119. _Stile._--The main uprights of a door, as A, A; B, B, B, rails; C, C, mullions; D, D, panels.

_Tie Beam._--See _Queen Post_.

120. _Trammel._--A very useful tool for drawing ellipses. It comprises a cross, A, with grooves and a bar, B, with pins, C, attached to sliding blocks in the grooves, and a pen or stylus, D, at the projecting end of the bar to scribe the ellipse.

121. _Turret._--A little tower, frequently only an ornamental structure at one of the angles of a larger structure.

122. _Transom._--A horizontal cross-bar, A, above a door or window or between a door and a window above it. Transom is the horizontal member, and if there is a vertical, like the dotted line B, it is called a _Mullion_. See _Stile_.

123. _Valley Roof._--A place of meeting of two slopes of a roof which have their sides running in different directions and formed on the plan of a re-entrant angle.

CHAPTER VIII

DRAWING AND ITS UTILITY

A knowledge of drawing, at least so far as the fundamentals are concerned, is of great service to the beginner. All work, after being conceived in the brain, should be transferred to paper. A habit of this kind becomes a pleasure, and, if carried out persistently, will prove a source of profit. The boy with a bow pen can easily draw circles, and with a drawing or ruling pen he can make straight lines.

REPRESENTING OBJECTS.--But let him try to represent some object, and the pens become useless. There is a vast difference in the use of drawing tools and free-hand drawing. While the boy who is able to execute free-hand sketches may become the better artist, still that art would not be of much service to him as a carpenter. First, because the use of tools gives precision, and this is necessary to the builder; and, second, because the artist deals wholly with perspectives, whereas the builder must execute from plane surfaces or elevations.

FORMING LINES AND SHADOWS.--It is not my intention to furnish a complete treatise on this subject, but to do two things, one of which will be to show, among other features, how simple lines form objects; how shading becomes an effective aid; how proportions are formed; and, second, how to make irregular forms, and how they may readily be executed so that the boy may be able to grasp the ideas for all shapes and structural devices.

[Ill.u.s.tration: _Fig. 125._]

[Ill.u.s.tration: _Fig. 126._]

[Ill.u.s.tration: _Fig. 127._]

a.n.a.lYSIS OF LINE SHADING.--In the demonstration of this work I shall give an a.n.a.lysis of the simple lines formed, showing the terms used to designate the lines, curves, and formations, so that when any work is laid out the beginner will be able, with this glossary before him, to describe architecturally, as well as mathematically, the angles and curves with which he is working.

HOW TO CHARACTERIZE SURFACE.--Suppose we commence simply with straight lines. How shall we determine the character of the surface of the material between the two straight lines shown in Fig. 125? Is it flat, rounded, or concaved? Let us see how we may treat the surface by simple lines so as to indicate the configuration.

[Ill.u.s.tration: _Fig. 128._]

[Ill.u.s.tration: _Fig. 129._]

[Ill.u.s.tration: _Fig. 130._]

[Ill.u.s.tration: _Fig. 131._]

CONCAVE SURFACES.--In Fig. 126 the shading lines commence at the upper margin, and are heaviest there, the lines gradually growing thinner and farther apart.

CONVEX SURFACES.--In Fig. 127 the shading is very light along the upper margin, and heavy at the lower margin. The first shaded figure, therefore, represents a concaved surface, and the second figure a convex surface. But why? Simply for the reason that in drawings, as well as in nature, light is projected downwardly, hence when a beam of light moves past the margin of an object, the contrast at the upper part, where the light is most intense, is strongest.

The shading of the S-shaped surface (Fig. 128) is a compound of Figs.

126 and 127.

[Ill.u.s.tration: _Fig. 132._]

SHADOWS FROM A SOLID BODY.--We can understand this better by examining Fig. 129, which shows a vertical board, and a beam of light (A) pa.s.sing downwardly beyond the upper margin of the board. Under these conditions the upper margin of the board appears darker to the vision, by contrast, than the lower part. It should also be understood that, in general, the nearer the object the lighter it is, so that as the upper edge of the board is farthest from the eye the heavy shading there will at least give the appearance of distance to that edge.

But suppose that instead of having the surface of the board flat, it should be concaved, as in Fig. 130, it is obvious that the hollow, or the concaved, portion of the board must intensify the shadows or the darkness at the upper edge. This explains why the heavy shading in Fig.

126 is at that upper margin.

FLAT EFFECTS.--If the board is flat it may be shaded, as shown in Fig.

131, in which the lines are all of the same thickness, and are s.p.a.ced farther and farther apart at regularly increasing intervals.

[Ill.u.s.tration: _Fig. 133._]

[Ill.u.s.tration: _Fig. 134._]

THE DIRECTION OF LIGHT.--Now, in drawing, we must observe another thing.

Not only does the light always come from above, but it comes also from the left side. I show in Fig. 132 two squares, one within the other. All the lines are of the same thickness. Can you determine by means of such a drawing what the inner square represents? Is it a block, or raised surface, or is it a depression?

RAISED SURFACES.--Fig. 133 shows it in the form of a block, simply by thickening the lower and the right-hand lines.

DEPRESSED SURFACES.--If, by chance, you should make the upper and the left-hand lines heavy, as in Fig. 134, it would, undoubtedly, appear depressed, and would need no further explanation.

FULL SHADING,--But, in order to furnish an additional example of the effect of shading, suppose we shade the surface of the large square, as shown in Fig. 135, and you will at once see that not only is the effect emphasized, but it all the more clearly expresses what you want to show.

In like manner, in Fig. 136, we shade only the s.p.a.ce within the inner square, and it is only too obvious how shadows give us surface conformation.

[Ill.u.s.tration: _Fig. 135._]

[Ill.u.s.tration: _Fig. 136._]

ILl.u.s.tRATING CUBE SHADING.--In Fig. 137 I show merely nine lines joined together, all lines being of equal thickness.

As thus drawn it may represent, for instance, a cube, or it may show simply a square base (A) with two sides (B, B) of equal dimensions.