7-15. Leader lines are used to indicate all linesand items on a blueprint which need additionalexplanation. Leader lines, to which a noteordimension is attached, have arrowheads, touchingthe edge of tke surface of an object, as illustratedin figure 7. These lines cannot be mistaken fordimension lines, since leader' lines are irregularlines or drawn at an angle.7-16. Seetiottai views. Frequently, a view doesnot giVe a clear impression of an object.Tliedifficulty lies with the invisible object lines, inwhich case a view into the interior of the objectwould lielp clarify the blueprint. Such a view ist)10fBREAKLINESLONG BREAK LINESSHORT BREAK LINES. Figure 18.illustration of break lines.called k sectional view, and it is Obtainedbyimagining that a portion of the exteriorof theobject has been removed to expose the internalconstruction. This type of section is determinedby the amount of the exterior removed. Asec-tional view is obtained by imagining that the,object is cut away, as if by sawing, and thepath "---of the saw is considered to be the cutting plane,1/4that is, the plane upon which the cut is made.7-17. When an object has been cutavay andone portion removed, the reniaining poitionthen crosshatched in the view. The term "cross-hatching," or section-lining, is used to distinguish4
the surfaces of material theoretically cut and ex-posed brthe cutting plane. Blueprintsare cross-hatched with the type of crosshatching (symbol)that represents. the actual material from Whichthe part or unit is made. Figure 14 isan illustraeltion of a, cross section in detail, as taken froman elevation plan.7-18. Sectiopal detail views. Sectional detailviews, with the aicof symbols, show in detail theconstruction, design, and materials used duringA'iUrBIRCHPLYWOODDOORS-t.I.....i.,IJBREAD BOARDS---,--.......,_..tDR.DR._I1IIIAELEVATIONFigure 14.Elevationthe fabrication of certain parts.Figure 15 showsthe cross section of a foundationdetail in largerscale than the orrginal plan. Thistype of detailyiew and many others are commonlyfound onplan views. They help to determinethe kind ofconstruction and how it I. to be installed.Thistype of drawing is one that will givethe heatingspecialist much information whichcannot begained from just a plain view floorplan. Therewill be a detail aheet with most blueprints,ordetail plans wiD be includedon each blueprintsheet. If the plan, has leader lineson it, it will-probably have a note, "See Detail Sketch A,B,or C," etc.and cross Section.SECTION A-A8.Symbols, Scales, and Piping Diagram8-1. To round out the informationon the pur-pose, construction, and use of blueprints by the' heating specialist,we have included in this sec-tion a discussion of symbols, scales, anda specifictype of print, the piping diagram.