CHAPTER 1 Introduction to Graphics Communication and SketchingChapter 1 is an introduction to the graphic language and tools of the engineer and technologist. The chapter explains why technical drawing is an effective way to communicate engineering concepts, relating past developments to modern practices, and examines current industry trends, showing why engineers and technologists today have an even greater need to master graphics communications. Concepts and terms important to understanding technical drawing are explained and defined, and an overview of the tools, underlying principles, standards, and conventions of engineering graphics is included. In addition, this chapter introduces you to sketching and the use of sketching for lettering. These techniques are expanded on in later chapters. Technical drawings are created using a variety of instruments, ranging from traditional tools, such as pencils, compass, and triangles, to the computer. Drawing tools are used to make accurate and legible drawings and models. Traditional drawing instruments are still important, especially for sketching; today, however, the computer can be used for most drawing and modeling requirements. This chapter is an introduction to: computer-aided design/drafting (CAD) systems, including the related hardware, software, and peripheral devices; and the traditional equipment normally used by engineers and technologists to create technical drawing models.
1.1In engineering, 92 percent of the design process is graphically based. The other 8 percent is divided between mathematics, and written and verbal communications. Why? Because graphics serves as the primary means of communication for the design process. |
1.2Drafting and documentation, along with design modeling, comprise over 50 percent of the engineer's time and are purely visual and graphical activities. Engineering analysis depends largely on reading engineering graphics, and manufacturing engineering and functional design also require the production and reading of graphics. |
1.3Engineering graphics can also communicate solutions to technical problems. Such engineering graphics are produced according to certain standards and conventions so they can be read and accurately interpreted by anyone who has learned those standards and conventions. |
1.4A designer has to think about the many features of an object that cannot be communicated with verbal descriptions. Technical drawings are a nonverbal method of communicating information. |
1.5Engineers are creative people who use technical means to solve problems. They design products, systems, devices, and structures to improve our living conditions. Technologists assist engineers and are concerned with the practical aspects of engineering in planning and production. Both engineers and technologists are finding that sharing technical information through graphical means is becoming more important as more nontechnical people become involved in the design/manufacturing process. |
THE IMPORTANCE OF ENGINEERING GRAPHICS Engineering graphics is a real and complete language used in the design process
for: - Communicating
- Solving problems
- Quickly and accurately visualizing objects.
- Conducting analyses.
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1.6-7A drawing is a graphical representation of objects and structures and is done using freehand, mechanical, or computer methods. Drawings may be abstract, such as the multiview drawings shown in, or more concrete, such as the very sophisticated computer model shown in. |
1.8Technical drawing is used to represent complex technical ideas with sufficient precision for the product to be mass-produced and the parts to be easily interchanged. |
1.11A engineering drawing is used for documentation. These types of drawings are used in manufacture, for planning, fabrication, and assembly. |
1.12The traditional design process involves organizing the creative and analytical processes used to satisfy a need or solve a problem. It is a sequential process that can be grouped into six major activities, beginning with identification of the problem and ending with documentation of the design. |
1.13This finite element model of a crane hook is used in the analysis of a part to determine where maximum stress and strain occurs when a part is placed under various load conditions. |
CHANGES IN THE ENGINEERING DESIGN PROCESS |
1.14The design process in U.S. industry is shifting from a linear, segmented activity to a team activity, involving all areas of business and using computers as the prominent tool. This new way of designing, with its integrated team approach, is called concurrent engineering. Concurrent engineering involves coordination of the technical and nontechnical functions of design and manufacturing within a business. Engineers must be able to work in teams. They must be able to design, analyze, and communicate using powerful CAD systems, and they must possess a well-developed ability to visualize, as well as the ability to communicate those visions to nontechnical personnel. |
1.15Geometric modeling is the process of creating computer graphics to communicate, document, analyze, and visualize the design process. There are various applications for a CAD database in the production of a product, using concurrent engineering practices. |
STANDARDS AND CONVENTIONS |
1.16Conventions are commonly accepted practices, rules, or methods used in technical drawing. |
1.17Standards are sets of rules that govern how technical drawings are represented. Standards allow for the clear communication of technical ideas. In the United States, the American National Standards Institute (ANSI) is the governing body that sets the standards used for engineering and technical drawings. Other professional organizations, such as the American Society for Mechanical Engineering (ASM), assist ANSI in developing technical graphics standards. |
1.18The alphabet of lines is a set of standard linetypes established by the American National Standards Institute (ANSI) for technical drawing. The alphabet of lines, and the approximate dimensions used to create different linetypes, which are referred to as linestyles when used with CAD. Listed below are the standard linetypes and their applications in technical drawings: Center lines are used to represent symmetry and paths of motion, and to mark the centers of circles and the axes of symmetrical parts, such as cylinders and bolts. Break lines are freehand lines used to show where an object is broken to reveal interior features. Dimension and extension lines are used to indicate the sizes of features on a drawing. Section lines are used in section views to represent surfaces of an object cut by a cutting plane. Cutting plane lines are used in section drawings to show the location of a cutting plane. Visible lines are used to represent features that can be seen in the current view. Hidden lines are used to represent features that cannot be seen in the current view. Phantom lines are used to represent a moveable feature in its different positions. |
1.19CAD software provides different linestyles for creating standard technical drawings. |
SPECIALISTS AND TECHNICAL DRAWINGSOver the years, specialized technical and engineering fields have developed to meet the needs of different industries and professions. Many of these specialized areas have also developed their own types of technical drawings. |
1.20Traditional mechanical drawing tools are still used in some places for the creation of traditional working drawings, but more often for sketching and informal drawing purposes. Traditional equipment includes: - Wood and mechanical pencils.
- Instrument set, including compass and dividers.
- 45- and 30/60-degree triangles.
- Scales.
- Irregular curves.
- Protractors.
- Erasers and erasing shields.
- Drawing paper.
- Circle templates.
- Isometric templates.
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1.21Mechanical pencils used for engineering drawings come in different lead sizes for drawing the different thicknesses of lines required on technical drawings. |
1.22Line weight refers to the relative darkness of the line. Uniform thickness means that the line should not vary.
Media are the surfaces upon which an engineer or technologist communicates graphical information. The media used for technical drawings are different types or grades of paper such as tracing paper, vellum, and polyester film. |
1.23Pencils are graded by lead hardness, from 9H to 7B: 9H is the hardest, and 7B is the softest. |
1.24Preprinted standard borders and title blocks on drafting paper are commonly used in industry.
Scales are used to measure distances on technical drawings. They are used to translate the size of real objects to dimensions that can comfortably fit on a sheet of paper. |
1.25-7The civil engineer’s scale is a decimal scale divided into multiple units of 10 and is called a fully divided scale. |
1.28A combination scale is one that has engineering, metric, and architectural components on a single scale. |
1.29-33The mechanical engineer’s scale is used to draw mechanical parts and is either fractionally divided into 1/16 or 1/32, or decimally divided into 0.1 or 0.02. |
1.34The lead in a compass is sharpened to a bevel using sandpaper. |
1.35The compass is used to draw circles and arcs of varying diameters. |
1.36A circle is drawn with a compass by first locating the center point, placing the needle at this point, and then leaning the compass in the direction you draw the circle. |
1.37A divider is used to transfer measurements. Unlike a compass, it has needles on both ends. |
1.38-9Templates are devices used to assist in the drawing of repetitive features, such as circles, ellipses, threaded fasteners, and architectural symbols. |
TECHNICAL AND COMPUTER-AIDED DRAWING TOOLS |
1.40-1A CAD system consists of hardware devices used in combination with specific software. The hardware for a CAD system consists of the physical devices used to support the CAD
software. |
1.42-3Future trends in technical and engineering graphics include the use of increased realism in graphic images through the use of high resolution displays, animation and simulation, 3-D stereo, holographic, and other virtual reality techniques. A general discussion can be had about the uses of visualization techniques in other areas. Many of your students may have had experience with computer/video/arcade games that make use of stereoscopic displays or other virtual reality (VR) techniques. Emphasize that advanced visualization techniques are important in a wide range of technical and scientific fields. An important concept to get across to students is that 3-D models created on the computer are meant to be virtual models of real world objects. Virtual reality is simply technology which strives to make this model and its surrounding environment as realistic as possible. The two main factors in the success of this experience are the fidelity and responsiveness of the virtual environment. Together, these two factors create a sense of immersion. For most VR systems, immersiveness is achieved with the following features: - Displays
- Tracking
- Tactile/audio feedback
- Response time
A distinction should be drawn between telepresence and VR. Typically, the VR system is uses an environment that is by and large synthetic. That is, it is created completely on the computer. Telepresence uses remote video equipment under the user's control to allow someone to experience a real environment that is in a remote location. |
1.44-52It is important to emphasize to the students the role that sketching plays in the engineering design process and how technical sketching differs from other types of sketching, such as those used in the fine arts. Many students have the mistaken impression that since sketching is less precise than manual drafting or CAD, it is less important. They don't realize that good sketching is an acquired skill and just because sketching is less precise doesn't mean that it should be sloppy or confusing. It may be worth noting that in many applications, technical sketches are required to follow the same graphics conventions that are imposed on formal drafted or CAD-produced drawings. |
1.53Note that though sketches can be created with any kind of drawing instrument on most any kind of paper, a good quality pencil and paper will help a beginning student. The instructor will have to decide their policy on the use of grid paper. Some feel it is a great way to support orthogonal and isometric line sketching in beginning (or advanced) students, but others feel it becomes a crutch which prevents them from becoming proficient on plain paper. The same decision goes for the use of tracing paper.
Another important issue is the use of straight edges. Students feel a tremendous need to produce that 'perfect' line. It is the opinion of this author that when you start using a straight edge, it is not longer a true sketch and you have lost much of the speed and flexibility advantage of sketching. |
1.54-7Students will come to your class with a truly diverse abilities to mentally create and manipulate graphic imagery (visualization). Either through their life experiences or through innate ability, some students are simply better at visualization than others. This does not mean that those who don't come to your class with strong skills can't be taught many of the skills presented in the text. What it does mean is that it will be worth your while to try to informally assess your student's visualization abilities; either through exercises presented in this chapter, direct observation, or other methods. The ability level of your students may influence the level of instruction needed to get students to an appropriate level of proficiency.
It is important to emphasize the dynamic qualities of the visualization process. Not only can this dynamic process be taking place solely in one' head, but also between the mind, the eyes, and some physical stimulus such as a drawing or an object. To apply these ideas in a more functional way, have your students experience this feedback loop. If you have already done some sketching exercises, then ask them to sketch a simple object in pictorial form. Now verbally describe changes you want them to make in their object (e.g. drill a hole through it, chamfer a corner, etc.). Ask them to first mentally imagine this operation and then sketch it. They can also do this completely on their own; have them start with a simple shape and then transform it into a common household object over a series of four or five sketches. |
1.58-9One of the most fundamental techniques in sketching is contour sketching. This technique defines the edges and contours of the object. The lines also define the boundary between the object and the surrounding space. |
1.60-1Variations on contour sketching include negative space sketching and upside-down sketching. |
1.62-5Encourage students to explore with different paper positions and body postures for drawing their lines. Emphasize the need to develop an appropriate balance of speed and accuracy in their linework. Encourage them not to look right at where the pencil is but to where the pencil is going. Intermediate points (especially for curved lines) can be of great help in creating lines that follow the marked path. |
1.66-8Get students comfortable with sketching out squares to guide circle and circular arc construction and rhomboids for elliptical curves. With the guide boxes in place, have students develop a feel for the proper curvature relative to the box. Trying to sketch without guide boxes is a common pitfall with beginning students and happens almost as often on small diameter circles as it does with large ones. |
PROPORTIONS AND CONSTRUCTION LINES |
1.69-75A logical extension of the use of guide boxes for circles and ellipses is the use of bounding (guide) boxes for developing the proportions of the sketch. Emphasize the importance of their use since all but the most gifted students are unlikely to have the visualization skills necessary to control the sketch proportions 'on the fly'. Encourage them to not only make small hash marks to mark distances, but to draw complete construction lines. These lines subdivide regions of the sketch and help the student refine the object from a rough whole to a detailed sketch. This process goes hand in hand with developing a student's visualization skills of looking at objects at various levels of detail; from the overall shape of an object to the details of particular features to where these features are located on the overall object. |
1.76-7Lettering is certainly one area where CAD has definitively increased the speed and accuracy of engineering and technical drawing. On the other hand, sketching done by hand cannot take advantage of the computer. For that reason, lettering has been placed in the chapter on sketching. In addition, this section also introduces many of the text variables you have at your disposal when using a CAD system. If you have not introduced CAD yet in your course, you may want to come back and review portions of this section when you do. |
1.78-9In addition to the ANSI standards, you may have other rules of thumb to convey to the students. Good and bad examples of lettering are always helpful in illustrating these principles. |
1.80Again, if the emphasis on your course is on CAD, you may want to only briefly touch on this section. By having all the students do a small amount of practice lettering in class, you can identify those needing help and have them do some remedial work out of class. If your primary interest in lettering is for use on sketches, you may not want to discuss lettering guides, since they slow down sketching much in the same way straight edges do. |
1.81Emphasize that guidelines (construction lines) are just as important in lettering as they are in sketching and drafting. You may decide, however, that those students who don't seem to be having too much trouble keeping their lettering aligned vertically, can skip putting in their vertical guidelines. |
1.82Cover not only the design style of each of the letters but also the numbers. There especially is a tendency to use non-standard designs for numbers among beginning students. Proper spacing is also something important to cover. Emphasize that the idea is to have uniform volume between the letters, not necessarily uniform distances between the nearest elements of the letters.
Though different companies and industries may use different computer lettering styles, Single Stroke Gothic is still the ANSI standard. (In AutoCAD, the closest equivalent is Roman Simplex). There can be a tendency among students to go a bit wild with their font choices (if given the opportunity) on a CAD system. |
1.83-7Within the same font, there are quite a few ways of varying the lettering, including plain, bold, slant, aspect, alignment (justification), etc. Point out times where it is appropriate to use these options. Explain to your students that the object is always drawn full scale in the CAD system, but that lettering may have to drawn at something other than the ANSI standard 3mm to account for print/plot scaling; that is, the 3mm standard is for the size on the printed/plotted page. |
1.88Examples from Chapter 10 on production drawings might to helpful in explaining the different areas where text is used on a drawing. Note that lettering within the drawing area should almost always conform to the ANSI standard 3mm, but that different sized and style text is often incorporated in other areas such as the titleblock.
If you can, point out examples of graphics that would clarified with the addition of a small amount of text and text notes that would be clarified by the addition of some graphic elements. |
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2002 McGraw-Hill Higher Education