7 15 leader lines are used to indicate all lines and

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7-15. Leader lines are used to indicate all lines and items on a blueprint which need additional explanation. Leader lines, to which a note or dimension is attached, have arrowheads, touching the edge of tke surface of an object, as illustrated in figure 7. These lines cannot be mistaken for dimension lines, since leader' lines are irregular lines or drawn at an angle. 7-16. Seetiottai views. Frequently, a view does not giVe a clear impression of an object. Tlie difficulty lies with the invisible object lines, in which case a view into the interior of the object would lielp clarify the blueprint. Such a view is t) 10 f BREAK LINES LONG BREAK LINES SHORT BREAK LINES . Figure 18. illustration of break lines. called k sectional view, and it is Obtained by imagining that a portion of the exterior of the object has been removed to expose the internal construction. This type of section is determined by the amount of the exterior removed. A sec- tional view is obtained by imagining that the, object is cut away, as if by sawing, and the path "--- of the saw is considered to be the cutting plane,1/4 that is, the plane upon which the cut is made. 7-17. When an object has been cut avay and one portion removed, the reniaining poition then crosshatched in the view. The term "cross- hatching," or section-lining, is used to distinguish 4
the surfaces of material theoretically cut and ex- posed brthe cutting plane. Blueprints are cross- hatched with the type of crosshatching (symbol) that represents. the actual material from Which the part or unit is made. Figure 14 is an illustra el tion of a, cross section in detail, as taken from an elevation plan. 7-18. Sectiopal detail views. Sectional detail views, with the aicof symbols, show in detail the construction, design, and materials used during A'iU r BIRCH PLYWOOD DOORS - t . I . . . .. i . , I J BREAD BOARDS ---,-- ....... , _..t DR. DR. _ I 1 I I I A ELEVATION Figure 14. Elevation the fabrication of certain parts. Figure 15 shows the cross section of a foundation detail in larger scale than the orrginal plan. This type of detail yiew and many others are commonly found on plan views. They help to determine the kind of construction and how it I. to be installed. This type of drawing is one that will give the heating specialist much information which cannot be gained from just a plain view floor plan. There will be a detail aheet with most blueprints, or detail plans wiD be included on each blueprint sheet. If the plan, has leader lines on it, it will- probably have a note, "See Detail Sketch A, B, or C," etc. and cross Section. SECTION A-A 8. Symbols, Scales, and Piping Diagram 8-1. To round out the information on the pur- pose, construction, and use of blueprints by the ' heating specialist, we have included in this sec- tion a discussion of symbols, scales, and a specific type of print, the piping diagram.

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