VIEWING OR CUTTING PLANE LINES

showing the pipe sleeve as it would look, viewed from one side, if it were cut exactly in half vertically. The surface of the imaginary cut is crosshatched with lines called section lines. According to DoD-STD-100C, “section lining shall be composed of uniformly spaced lines at an angle of 45 degrees to the baseline of the section. On adjacent parts, the lines shall be drawn in opposite directions. On a third part, adjacent to two other parts, the section lining shall be drawn at an angle of 30 to 60 degrees.” The cross-hatching shown in figure 3-37 could be used on any drawing of parts made of only one material (like machine parts, for example, which are generally made of metal). The cross-hatching is the symbol for metals and may be used for a section drawing of any type of material. A section like the one shown in figure 3-37, which goes all the way through and divides the object into halves, is called a full section. If the section showed the sleeve as it would look if cut vertically into unequal parts, or cut only part way through, it would be a partial section. If the cut followed one vertical line part of the way down and then was offset to a different line, it would be an offset section. VIEWING OR CUTTING PLANE LINES VIEWING PLANE LINES are used to indicate the plane or planes from which a surface or several surfaces are viewed. CUTTING PLANE LINES are used to indicate a plane or planes in which a sectional view is taken. Section views are used to give a clearer view of the interior or hidden feature of an object that normally cannot be clearly observed in conventional outside views. A section view is obtained by cutting away part of an object to show the shape and construction at the cutting plane. Notice the CUTTING PLANE LINE AA in figure 3-38, view A. It shows where the imaginary cut has been made. The single view in figure 3-38, view B, helps you to visualize the cutting plane. The arrows point in the direction in which you are to look at the sectional view. 65.25 Figure 3-38.-Action of a cutting plane. Figure 3-38, view C, is a front view showing how the object would look if it were cut in half. The orthographic section view of section A-A, figure 3-38, view D, instead of the confusing front view in figure 3-38, view A, is placed on the drawing. Notice how much easier it is to read and understand. Note that hidden lines behind the plane of projection are omitted in the sectional view. These lines are omitted by general custom, the custom being based on the fact that the elimination of hidden lines is the basic reason for making a sectional view. However, lines that would be visible behind the plane projection must be included in the section view. Cutting plane lines, together with arrows and letters, make up the cutting plane indications. The arrows at the end of the cutting plane lines are 3-25