viii The instructional design of the text contains student-focused learning tools to help you succeed. The various features designed for the textbook are explained here. Features of the Textbook Copyright Goodheart-Willcox Co., Inc. 223 Sectional Views UNIT 13 Learning Objectives After studying this unit, you will be able to: ■ Explain the terms sectional view, cutting plane, and cutting-plane line. ■Identify various patterns of section lines. ■Identify full, offset, half, revolved, removed, and broken-out sections. ■Complete sketches of sectional views. Key Terms break line broken-out section cutting plane cutting-plane line full section half section offset section removed section revolved section section line sectional view A sectional view is a view that shows how an object would appear if a portion were cut away by an imaginary plane to reveal the interior details. The exposed (cut) surface is emphasized by the use of sec- tion lines. See Figure 13‑1. Working with Sectional Views Using sectional views is an effective way to show inte- rior features that would be complicated or confus- ing if described entirely by hidden lines. On a print, a sectional view may serve as one of the principal views—front, top, or right side—or it can be used as an additional view. A sectional view is developed by first passing a cutting plane through the part. A cutting plane is an imaginary plane that divides an object to produce a sectional view. Then, the section of the part nearest the viewer is removed, thereby revealing a direct and clear view of the interior shape. See Figureline 13‑1. Cutting-Plane Line The location of the imaginary cutting plane is indi-, cated by a heavy line called a cutting-plane line Cutting plane Goodheart-Willcox PublisherGoodheart-Willcox Figure 13-1. A sectional view showing how an imaginary cut- ting plane is used to cut away a portion of a part to reveal interior features. In this example, the cutting plane is located at the center of the part and the front half is cut away. Copyright Goodheart-Willcox Co., Inc. 23 Line Usage UNIT 3 Learning Objectives Aft er studying this unit, you will be able to: ■ Describe the purposes of the various types of lines found on prints. ■Identify the various types of lines found on prints. ■Locate corresponding lines or surfaces in various views. Key Terms alphabet of lines American Society of Mechanical Engineers (ASME) break line centerline chain line cutting-plane line dimension line dimensioning drawing standards extension line hidden line leader line phantom line section section line stitch line symmetry line viewing-plane line visible line As new ideas develop into useful products, they require precise drawings of parts. Drawings must be consistent so they are readable across the industry. Drawing standards are documented practices used to develop drawings. The American Society of Mechanical Engineers (ASME) is an independent, not-for-profit organization that defines drawing stan- dards used by the industry for the development of engi - neering drawings. One of the standards is ASME Y14.2, titled Line Conventions and Lettering. This standard establishes guidelines for specific types of lines used on drawings. Line types used on drawings make up a system referred to as the alphabet of lines.Inthissystem,eachtypein3‑1.eFigur of line has an intended purpose, as shown Visible line Thick Thick Thick Thick Thick Thick Thin Thin Thin Thin Thin Thin Thin Thin (Width 0.6 mm) (Width 0.3 mm) All thin Leader Dimension line Extension line Hidden line Section Centerline Symmetry line Dimension line Extension line Leader line Cutting-plane or Viewing-plane lines Break line (long) Break line (short) Stitch line Phantom line Chain line Publisher Figure 3-1. The alphabet of lines is based on conventions established in the ASME Y14.2 standard. Unit Opening Materials Each unit opening contains a list of learning objectives and a list of technical terms. Learning Objectives clearly identify the knowledge and skills to be obtained when the unit is completed. Key Terms list the technical terminology to be learned in the unit. Additional Features Additional features are used throughout the body of each unit to further learning and knowledge. Illustrations have been designed to clearly and simply communicate the specific topic. The figures throughout the book comply with current industry standards and highlight important terms students must understand. Real industrial prints found at the end of most units help students understand how the concepts in the text relate to a career in manufacturing. Pro Tips provide students with advice and guidance that is especially helpful to beginning print readers. 268 Machine Trades Print Reading Copyright Goodheart-Willcox Co., Inc.touchescut-the Drawing Interpretation Goodheart-Willcox Publisher Figure 15-15. When a tolerance specification includes the LMC modifier, the specified tolerance value applies when the feature is at LMC. At different allowable hole sizes, the tolerance increases as the hole size varies from LMC. Ø .750–.752 located tolerancepreviously.010a zone within Drawing Interpretation Goodheart-Willcox Publisher Figure 15-16. When a tolerance is specified at RFS, the specified tolerance value remains constant and applies regardless of the actual size of the feature. 140 Machine Trades Print Reading Copyright Goodheart-Willcox Co., Inc. Extra material around a hole is required to ream an accurate size hole to a fine finish. The basic material allowance is .0156″mm) (0.3968 mm) for diameters under 1″ (25.4 and .0313″ (0.7938 mm) or more for diameters greater than 1″ (25.4 mm). PRO TIP Counterbored Holeenlarging Counterboring is the process of formed hole cylindrically to a specific diameter and depth. Counterboring produces a flat bottom surface. Its purpose is to provide a recessed hole for fitting fas- tener heads or seating bearings and pins. The specifications for a counterbored hole appear on two lines. See Figure 9‑9. The first line specifies information for the small hole. The information is given in the following order: the diameter symbol, the size of the small hole diameter, the depth symbol, and the depth size. The depth symbol and depth size are only included if required. The second line of the counterbore specification gives information for the counterbored The information is given the following order: the counterbore symbol, the diame - ter symbol, the size of the counterbore diameter, the depth symbol, and the depth size. Countersunk Holeof Countersinking is the process enlarging the entrance a hole conically to recess the head of a fastener, such as a flat screw. A countersunk hole has a specified angle to match the angle of the fastener’s head. The typical angle used for fasteners is 82°. However, 100° is common for fasteners on thin materials to provide additional surface area for fastening. The specifications for a countersunk hole appear on two lines. See Figure 9‑10. The first line spec - ifies information for the small hole in the follow- ing order: the diameter symbol, the size of the small hole diameter, the depth symbol, and the depth size (the depth symbol and depth size are only included if required). This Means this Goodheart-Willcox Publisher Figure 9-7. Representation of a bored hole. Hole is ÿrst drilled to a ∅ .562, then ÿnished with a reamer to ∅.578 This Means this Goodheart-Willcox Publisher Figure 9-8. Older drawings included specifications for reamed holes. Means this Counterbore symbol This Goodheart-Willcox Publisher Figure 9-9. Specifications for a counterbored hole. Unit 13 Sectional Views 225 Copyright Goodheart-Willcox Co., Inc. used on all types of materials, including nonmetallic as well as metallic materials. See Figurehole. 13‑6 . In general use, however, the section lines for cast iron are applied to detail drawings of a separate part. Full Section A full section is a sectional created by passing a cutting-plane line through entire object in a straight line, as shown in Figureofanviewhead 13‑7 . Lines that were hidden are now exposed and shown as visible lines. Only the edges that the cutting-plane line are shown. The hidden lines behind ting-plane line are generally omitted. They would merely add confusion to the interior detail. PRO TIPin When reading a sectional view, first determine the direction of the cutting-plane line on the correspond- ing view. Then transfer the details behind the cut- ting-plane line to the sectional view. The transferring of points on the cutting-plane line to the sectional view locates the interior detail. Note that the outer edges of Poor Practice Poor Practice Preferred Practice Goodheart-Willcox Publisher Figure 13-5. The two examples on the left illustrate poor practice because section lines are drawn parallel with the part object lines. The example on the right shows the correct way to represent section lining. Magnesium Aluminum Rubber, Plastic, Titanium Marble, Slate, Glass, Porcelain Cast Iron (general purpose) Steel Bronze, Brass, Copper Zinc, Lead, Babbitt, Alloys Electrical Insulation Refractory Metal Goodheart-Willcox Publisher Figure 13-6. Section line patterns for various materials. Cutting-plane line Section lines Pulley Cover Goodheart-Willcox Publisher Figure 13-7. Examples of full sections of parts.