Engineering Drawing - Chapter 1 & 2 PDF

CHAPTER ONE INTRODUCTION TO GRAPHIC COMMUNICATIO N Group 1  Objectives: At the end of this chapter students should be able to:  Define graphic communication  Mention types of drawing  Explain the difference between different types of drawings  Mention some of the applications of technica...

CHAPTER ONE INTRODUCTION TO GRAPHIC COMMUNICATIO N Group 1  Objectives: At the end of this chapter students should be able to:  Define graphic communication  Mention types of drawing  Explain the difference between different types of drawings  Mention some of the applications of technical drawings  1.1 Drawing A drawing is a graphic representation of an object, or a part of it, and is the result of creative thought by an engineer or technician. When one person sketches a rough map in giving direction to another, this graphic is communication. Graphic communication involves using visual materials to relate ideas. Drawings, photographs, slides, transparencies, and sketches are all forms of graphic communication. Any medium that uses a graphic image to aid in conveying a message, instructions, or an idea is involved in graphic communication. One of the most widely used forms of graphic communication is the drawing. 1.1.1 Artistic Drawings Artistic Drawings range in scope from the simplest line drawing to the most famous paintings. Regardless of their complexity, artistic drawings are used to express the feelings, beliefs, philosophies, and ideas of the artist. 1.1.2 Technical Drawings Thetechnical drawing , on the other hand, is not subtle, or abstract. It does not require an understanding of its creator, only an understanding of technical drawings.  A. Types of Technical Drawings Technical drawings are based on the fundamental principles of projections. projection is a drawing or A representation of an entity on an imaginary plane or planes. This projection planes serves the same purpose in technical drawing as is served by the movie screen. A projection involves four components.  Four 1. The actual object that the drawing or projection Component represents 2. The eye of the viewer looking at the object s of 3. The imaginary projection plane 4. Imaginary lines of sight calledProjectors Projection Two Broad Types of Projections Parallel Projection Parallel Projection Parallel Projection is a type of projection where the line of sight or projectors are parallel and are perpendicular to the picture planes. It is subdivided in to the following three categories: Orthographic, Oblique and Axonometric Projections. Orthographic Projections Orthographic projections are drawn as multi-view drawings, which show flat representations of principal views of the subject. Oblique Projections Oblique Projections actually show the full size of one view. Axonometric Projections Axonometric Projections are three- dimensional drawings, and are of three different varieties: Isometric, Dimetric and Trimetric. Perspective Projection Perspective projections are drawings which attempt to replicate what the human eye actually sees when it views an object. There are three types of perspective projections: One-point, Two-point and Three-point-Projections. One Point Projection One point perspective is defined as a drawing technique and type of linear perspective that uses a single vanishing point on the horizon line to give an illusion of depth and distance in artworks. Two-Point Projection Two Point Perspective is a systematic way of drawing box- like objects or anything that can be logically arranged into a geometric, grid-like structure. Three-Point Projection In a nutshell, three-point perspective is an extension of linear perspective in which three vanishing points are used in a drawing as guides to create a realistic representation of depth and perspective.  B. Purpose of Technical Drawings To appreciate the need for technical drawings, one must understand the design process. The design process is an orderly, systematic procedure used in accomplishing a needed design. C. Application of Technical Drawing Technical drawings are used in many different applications. They are needed in any setting, which involves design, and in any subsequent forms of conversion process. The most common applications of technical drawings can be found in the fields of manufacturing, engineering and construction.  CHAPTER TWO DRAWING EQUIPMENTS AND THEIR USE Group 1 Objectives: At the end of this chapter students should be able to:  List the main drawing equipments  Discuss the use of different drawing equipments 2.1 Introduction To record information on paper instruments and equipments are needed. Engineering drawing is entirely a graphic language hence instruments are essentially needed. Drawing must be clear, neat and legible in order to serve its purpose. Hence it is extremely important for engineers to have good speed, accuracy, legibility and neatness in the drawing work.  2.2 Important Drawing Equipments All drawings are made by means of various instruments. The quality of drawing depends to a large extent on the quality, adjustment and care of the instruments.  Drawing paper is the paper, on which drawing is to be made. All engineering drawings are made on sheets of paper of Drawing strictly defined sizes, which are set forth in the U.S.S.R standards. The use of standard size saves paper and Paper ensures convenient storage of drawings. Now a day, A3 and A4 are the most commonly used paper sizes. The U.S.S.R standard establishes five preferred sizes for drawings as tabulated bellow: Size 11 12 22 24 44 designation Sheet 297x210 297x420 594x420 594x841 1,189x841 dimensions in mm Corresponding A4 A3 A2 A1 A0 designation of paper sheets according to the U.S.S.R Standard (for references) Title block is a rectangular frame that is located at the bottom of the sheet. It is recommended that space should be provided in all title blocks for such information as description of title of the drawing, dates, designer (drawer), and name of enterprise or educational institute, size (scale) Triangles (setsquares) They are used to construct the most common angles (i.e. 300, 450, 600) in technical drawings. The 450 x 450 and 300 x 600 triangles are the most commonly used for ordinary work. T- square It is used primarily to draw horizontal lines and for guiding the triangles when drawing vertical and inclined lines. It is manipulated by sliding the working edge (inner face) of the head along the left edge of the board until the blade is in the required position. French curve It is used to draw irregular curves that are not circle arcs. The shape varies according to the shape of irregular curve. Protractor It is used for laying out and measuring angle. Scale (ruler) A number of kinds of scales are available for varied types of engineering design. Scales with beveled edges graduated in mm are usually used.  Pencil The student and professional man should be equipped with a selection of good, well- sharpened pencil with leads of various degrees of hardness such as: 9H, 8H, 7H, and 6H (hard); 5H& 4H (medium hard); 3H and 2H (medium); and H& F (medium soft). The grade of pencil to be used for various purposes depends on the type of line desired, the kind of paper employed, and the humidity, which affects the surface of the paper. Standards for line quality usually will govern the selection. a 6H is used for light construction line. a 4H is used for re-penciling light finished lines (dimension lines, center lines, and invisible object lines) a 2H is used for visible object lines a F and H are used for all lettering and freehand work. Compass It is used to draw circles and arcs both in pencil and ink. It consists of two legs pivoted at the top. One leg is equipped with a steel needle attached with a screw, and other shorter leg is, provided with a socket for detachable inserts. Divider Used chiefly for transferring distances and occasionally for dividing spaces into equal parts. i.e. for dividing curved and straight lines into any number of equal parts, and for transferring measurements. Template A template is a thin, flat piece of plastic containing various cutout shapes. It is designed to speed the work of the drafter and to make the finished drawing more accurate. Templates are available for drawing circles, ellipses, plumbing’s, fixtures etc. Drawing board Drawing board is a board whose top surface is perfectly smooth and level on which the drawing paper is fastened. Clinograph Clinograph (Adjustable set square) its two sides are fixed at 900 and the third side can be adjusted at any angle. Rubber or eraser Rubber or eraser extra lines or curves which are not required in the drawing are to be rubbed out or erased. Hence a rubber or eraser are required in the drawing work. Erasers are available in many degrees of hardness, size and shape. Eraser shield Eraser shield it is an important device to protect lines near those being erased. It is made up of thin metal plate in which gaps of different widths and lengths are cut. Tracing paper Tracing paper it is a thin transparent paper. Figures below it can be seen easily and traced out in pencil ink. Drawing Ink Drawing ink it is used for making drawings in ink on tracing paper. Thank you for May God Bless You! listening!