CHAPTER 1 Introduction to Graphics Communication and Sketching

 

1.1 INTRODUCTION

Chapter 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.

                In 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.

                Drafting 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.

                Engineering 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.

                A 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.

                Engineers 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.

1.2 the importance of graphics in the design process

Engineering graphics is a real and complete language used in the design process for:

                1.  Communicating 

                2.  Solving problems 

                3.  Quickly and accurately visualizing objects. 

                4.  Conducting analyses.

                A drawing is a graphical representation of objects and structures and is done using freehand, mechanical, or computer methods.  Drawings may be abstract (e.g., multiview drawings), or more concrete (e.g., very sophisticated computer models).

                Technical 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.

1.3 THE traditional DESIGN PROCESS

                An engineering drawing is used for documentation.  These types of drawings are used in manufacturing, for planning, fabrication, and assembly. 

                The 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.

                This 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.

1.4 the design process using concurrent engineering

                The 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.

                Geometric 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.

1.5 STANDARDS AND CONVENTIONS

                Conventions are commonly accepted practices, rules, or methods used in technical drawing.

                Standards 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.

1.6 ALPHABET OF LINES

                The 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.

                CAD software provides different linestyles for creating standard technical drawings.

1.7 SPECIALISTS AND TECHNICAL DRAWINGS

                Over 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.

1.8 technical drawing TOOLS

                The tools used in engineering and technical graphics have evolved from pencils, T-squares, compasses, and triangles to computer-based tools. Computer-aided design/drafting (CAD) is now the standard.

1.9 Computer-aided DRAWING TOOLS

                A 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.

                The central processing unit (CPU) is the hardware device that runs the computer programs and controls the various attached input and output devices.

                Operating systems are programs that control the internal operations of the computer, such as the memory, storage drives, input and output devices, and data transmission circuitry.  Software comprises the written and coded instructions that govern the operation of the computer and the functions it performs.

                A display device is a type of output device, that is, a device through which information flows from the computer "out” to the user.  A vector device locates the endpoints of a line and then draws the line by electronically charging a continuous stream of phosphors on the screen. A raster device, which is the most common, creates an image by electronically charging individual points called pixels, which are arranged in horizontal rows.  In a CAD system, the display device can be thought of as the drawing paper or medium upon which technical drawings and models are produced.

                Movement of a screen cursor is controlled by an input device, such as a keyboard, tablet, or mouse, through which information flows from the user "in" to the computer.

                A tablet is an input device used to control cursor movement and select menu items.

                A scanner is an input device used for converting a drawing created with traditional tools to a CAD drawing.

                The keyboard is a device used to input alphanumeric data and to make CAD menu selections.

                The mouse is an input device used to control cursor movement and to make menu selections.

                The output devices used to make hard copies of the drawings created on screen are categorized as: printers, plotters, or film recorders.

                A printer is an output device that creates characters, numbers, and graphics on paper.  Printers are used with CAD to create check prints. A check print is a low quality hard copy made at high speed. 

                Inkjet printers use narrow nozzles to spray ink onto the paper.

                Laser printers use a laser beam to record an image in the form of tiny dots on a light sensitive drum.

                A storage device is used to store information on a specific medium and retrieve that information as needed.  Storage devices are combination input/output (I/O) devices, and are grouped into five categories:

                Storage devices are usually either fixed or removable. A fixed drive might be the hard disk inside your computer. Removable drives (media) include magnetic media such as Zip disks and floppy disks and optical media such as CDs and DVDs.

1.10 TRADITIONAL TOOLS

                Traditional tools are devices used to assist the human hand in making technical drawings.

                Mechanical drawings are started by taping the drawing paper to the working surface. A straightedge, such as a T-square, parallel edge or drafting machine, is used to draw horizontal lines.

                Paper is positioned on the drawing surface by aligning the bottom of the paper to the horizontal blade of the drafting machine, and then taping the paper at the corners.

                The protractor is used to measure and mark angles on a technical drawing.

                Drafting machines are devices that supplement the T-square, triangles, protractors, and scales.  The protractor head on a drafting machine is used to draw lines at any angle.

                The adjustable triangle can be set to a specified angle.

                Mechanical pencils used for engineering drawings come in different lead sizes for drawing the different thicknesses of lines required on technical drawings.

                Line weight refers to the relative darkness of the line. Uniform thickness means that the line should not vary.

                Pencils are graded by lead hardness, from 9H to 7B:  9H is the hardest, and 7B is the softest.

                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.

                Preprinted standard borders and title blocks on drafting paper are commonly used in industry.

                Drafting triangles are either 30/60- or 45- degree triangles and come in various sizes.

                By combining the straight edges with the 45-, and 30/60-degree triangles, you can draw lines at any 15-degree increment.

                Scales are used to measure distances on technical drawings.  An architect’s scale is used to create drawings of structures, such as a building or a factory floor layout.  The civil engineer’s scale is a decimal scale divided into multiple units of 10 and is called a fully divided scale.

                Steps in reading an architect's scale.

                The civil engineer's scale is a decimal scale divided into multiple units of 10 and is called a fully divided scale.

                Steps in reading a civil engineer's scale.

                The 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.

1.11 what you will learn

                In this text you will explore six important areas of technical graphics:
1. Visualization

                2. Graphic theory

                3. Standards

                4. Conventions

                5. Tools

                6. Applications

1.12 Future trendS

                Future 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 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.

1.13 SUMMARY

As a student of engineering graphics, you will study and learn to apply the tools used to create engineering drawings and models. Even more important, you will also learn the underlying principles and concepts of engineering graphics, such as descriptive geometry. You will also learn the standards and conventions that will enable you to create drawings and models that can be read and accurately interpreted by engineers or technologists anywhere. 
The tools used for technical drawing include traditional ones, such as the triangle and the compass, and CAD. Traditional tools are used to make technical drawings by hand, and it takes practice and repetition to become proficient at their use. Although with CAD there is less emphasis on developing good technique, it still requires practice and repetition to attain proficiency.
The mind uses many visualization tools, working in concert, to interpret the world. The mind engages in constant problem solving in the interpretation process. Part of this problem-solving process is automatic. However, you can develop numerous sketching and modeling techniques that will help. With a better understanding of how the mind interprets what it receives, you can use conscious mental power to assist in this process. You can also learn to bring physical processes into play. For example, you may be able to pick up an object and rotate it, to gain a better understanding of the object. More importantly, you may be able to create a sketch that will help you in the visual problem-solving process.