Section-Lining.
Cross-hatching has been defined in the “preliminary definitions” to drawing; this term represents the practice of drawing diagonal lines representing the interior of an object, shown as a piece cut in half or when a piece is broken away. This is done to make more of the parts show, or to exhibit more clearly the nature of the materials; hence section lining and cross-hatching tell the same thing, i. e., the drawing of diagonal lines, usually at an angle of 45°, to show that the object is broken away and the interior designed to be represented.
Cast iron.
Fig. 251.
Wrought iron.
Fig. 252.
Steel.
Fig. 253.
Composition.
Fig. 254.
Vulcanite.
Fig. 255.
Wood.
Fig. 256.
Leather.
Fig. 257.
Brick.
Fig. 258.
Fig. 259.
[Figs. 251 to 258], inclusive, show the section lining and cross-hatching by which it is customary to represent the various materials entering into a construction.
In [fig. 259] is outlined a representation of a section of a cog-wheel; section 1 being the wood cogs; 2, the iron wheel, and 3 the wedges at the root of the gear. It would be impossible to convey the same ideas by ordinary plan or elevation drawing; all the objects on the same page are more clearly represented by the use of section lines or cross-hatching.
Sectioning is executed by drawing a series of parallel lines about 3⁄32 inches apart. Lay the 45° triangle on the upper edge of the T-square and draw the top-most line of the sectioning. Then slide the triangle along the T-square for each successive line. The sectioning should be inked in without previous penciling and the lines should be finer than the lines of the general drawing.
Various devices are in use for mechanically equalizing the distances in section lining, but the trained eye is the most practical method. When two abutting pieces are sectioned, the section lining on one piece slants in an opposite direction to that on the other.
To draw an object to be sectioned on both sides of its center line, only one side is sectioned, while the other side is drawn in full.
Sections are necessary in nearly all machine drawings; they are usually taken horizontally or vertically, but they may be taken in any direction; the position of a section should be shown by a line upon the object; this line is called the cutting plane.
In [fig. 261] is shown the hub of a wheel, it is also a sample of work for practice.
Fig. 260.
Fig. 261.
[Fig. 260] shows the mode of representing two different materials in one plane, or a section may be represented by the darker portion, and the lighter shaded portion being a surface resting on the section.
[Fig. 261] shows the section of a shaft surrounded by the surface of a wheel.