Introduction to Engineering Drawing PDF

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Introduction to Engineering Drawing Drawing 

Drawing is a graphic representation of an object, or a part of it.

Engineering drawing 

An engineering drawing is a means of clearly and concisely communicating all the information necessary to transform an idea or a concept in to reality.



Therefore, an engineering drawing often contains more than just a graphic representation of its subject. It also contains dimensions, notes and specifications.

Elements of Engineering Drawing Engineering drawing are made up of graphics language and word language. Graphics language: Describe a shape (mainly). Word language: Describe an exact size, location and specification of the object.

Characteristics of Good Drawing 1. Drawing should be clear, simple and clean 2. Should agree with the actual measurements by the accurately drawn scaled measurements.

3. Exact information should be provided in order to carry out the work at site without scaling for missing measurements. 4. Only minimum notes to support the drawings should be indicated in the drawings. 5. Sufficient space should be provided between the views so as to mark the dimensions without cram.

Drawing Instruments and their use 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. 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. i. Drawing Paper Drawing paper is the paper, on which drawing is to be made. All engineering drawings are made on sheets of paper of strictly defined sizes, which are set forth in the U.S.S.R standards. The use of standard size saves paper and ensures convenient storage of drawings. Nowadays, 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: Description of the size of drawing paper 22 24 44

Size desig natio n Shee t dime nsio ns in mm Correspo

11

12

29 7x 21 0

29 7x 42 0

59 4x 42 0

59 4x 84 1

1,18 9x8 41

nding

A4

A3

A2

A1

A0

designati on paper sheets

of

accordin g to the U.S.S.R Standard (for refer ence s)

A4

A3

29 mm 7

420mm 297mm

210mm A4 and A3 standard papers

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)

Boarder line

A4 Title block

A3

Title block

Boarder line Sample for title block TITLE DR.BY GUTEMA KETEMA CHECK.BY ASSIGN. NO. SCALE

INSTIT. AU

DATE 02/02/2003

ii. 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. They are shown in the fig. 2.2 below. iii. 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.

T-square iv. French curve It is used to draw irregular curves that are not circle arcs. The shape varies according to the shape of irregular curve.

v. Protractor It is used for laying out and measuring angle.

Protractor vi. 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.

vii. Pencil The student and professional man should be equipped with a selection of good, wellsharpened 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. For instance, ♦ 6H is used for light construction line. ♦ 4H is used for re-penciling light finished lines

♦

(dimension lines, center lines, invisible object lines) 2H is used for visible object lines

and

F and H are used for all lettering and ♦ freehand work. viii. 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. viiii. 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.

Compass and divider

ix. 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. Templates come in many sizes to fit the scale being used on the drawing. And it should be used wherever possible to increase accuracy and speed. x. Drawing Board Drawing board is a board whose top surface is perfectly smooth and level on which the drawing paper is attached xi. 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 is required in the drawing work. Erasers are available in many degrees of hardness, size and shape. 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 – it is a thin transparent paper. It can be seen easily and traced out in pencil ink. Drawing ink- it is used for making drawings in ink on tracing paper.

General Instructions Regarding Preparation of Drawing Sheets •

Cleaning the instruments

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Attaching the drawing sheet to drawing table after correct alignment through the drafting edge

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BORDER LINES: •

Perfectly rectangular working space is determined by drawing the border lines.

•

These may be drawn at equal distances of about 0.5-inch from top, bottom and right-hand edges of the paper and about 1-inch from the left-hand edge.

•

TO DRAW BORDER LINES •

Marking the points and draw top and bottom horizontal lines with the help of drafting edge or T-square

•

•

Marking points on horizontal borders for the vertical lines.

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Erasing the extra lengths of lines beyond the points of intersection.

The title block must be drawn in the right-hand bottom corner with 4-inch height and 4-6inch long, in which following may be written

•

•

Your name

•

Title of the drawing

•

Your Class & Section along with the registration/roll number

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Date of submission

SPACING OF DRAWING: •

If one drawing is to be drawn on a sheet it should be in the center of the working space.

•

For more than one figure, the space should be divided into suitable blocks and each figure should be drawn in the center of its respective block.

Standard Engineering Lettering •

Writing of titles, dimensions, notes and other important particulars on a drawing is called lettering.

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Lettering is used to provide easily readable information to supplement a drawing in the form of notes and annotations.

•

Lettering is an essential element in both traditional drawing and Computer Aided Design (CAD) drawing. Thus, it must be written with:

Legibility – shape & space between letters and words. Uniformity – size & line thickness. •

It should be done in plain and simple style so that it could be done freehand and speedily.

•

Use of drawing instruments in lettering takes considerable time and hence it should be avoided.

Single Stroke Letters •

It is recommended to use single-stroke lettering in engineering drawing.

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The word single-stroke should not be taken to mean that the letter should be made in one stroke without lifting the pencil. It actually means that the thickness of the line of the letter should be such as is obtained in one stroke of pencil.

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Single stroke letters are of two types: o Vertical o Inclined

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Inclined letters lean to the right, the slope being 75 degrees with the horizontal.

Basics of Single Stroking

Lettering Instructions •

Horizontal lines should be drawn from LEFT TO RIGHT

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Vertical or inclined lines, from TOP TO BOTTOM.

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Alphabet and numerals should neither touch each other nor the lines.

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Letters should be so written that they appear upright from the bottom edge, except when they are used for dimensioning. For dimensioning, they may appear upright from the bottom edge or the right-hand side or the corner in between.

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Letters should be so spaced that the area between letters appear equal.

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Its not necessary to keep the clearances between adjacent letters equal, e.g. LA, TV or Tr.

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Obtain constant line density. All letters should be uniform in shape, size, shade and spacing.

Spacing Uniformity in spacing of letters is a matter of equalizing spaces by eye. •

The background area between letters, not the distance between them, should be approximately equal.

•

Words are spaced well apart, but letters within words should be spaced closely.

•

For either upper case or lower-case lettering, make the spaces between words approximately equal to a capital O.

Dimensioning  A dimensioned drawing should provide all the information necessary for a finished product or part to be manufactured.  Dimensions are always drawn using continuous thin lines. Two projection lines indicate where the dimension starts and finishes. Projection lines do not touch the object and are drawn perpendicular to the element you are dimensioning.  In general units can be omitted from dimensions if a statement of the units is included on your drawing.  The general convention is to dimension in mm's, however in civil engineering inch or foot is more commonly used  All dimensions less than 1 should have a leading zero. i.e. .35 should be written as 0.35 Elements of Dimensioning •

Extension line

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Dimension line

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Leader line

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Arrowheads

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Dimensions

Rules of Dimensioning

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There should be only one dimension between two extension line on a single dimension line

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All dimensions should be placed outside the views to the extent possible

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The two dimensioning systems should not be mixed in a single drawing

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The same unit of length should be used throughout the drawing, although the scale may be varied if needed

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Dimension lines must not cross each other or with any other line of the object, however extension lines may cross each other or any other line of the object

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Drawing should be fully dimensioned, and there should not be any need to measure or calculation for any dimension

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Repeated dimensions should be avoided

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Avoid dimensioning hidden lines

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Keep the dimension lines 6-8 mm away from the object line and from each other

Drawing scales Scale is the ratio of the linear dimension of an element of an object shown in the drawing to the real linear dimension of the same element of the object. Engineering Scale Engineering scale is represented by writing the relation between the dimension on the drawing and the corresponding actual dimension of the object itself. It is expressed as  1mm=1mm  1mm=5 m, 1mm=8km  1mm=0.2mm, 1mm=5µm The engineering scale is usually written on the drawings in numerical forms. Designation of a scale consists of the word “SCALE” followed by the indication of its ratio, as follows:

Dimension numbers shown in the drawing correspond to “true size” of the object and they are independent of the scale used in creating that drawing. Scales and Sizes • 16 Scale = Full Size 12” = 1’- 0”. (standard ruler) • 3” = 1’- 0” = Quarter Size (divide 3”/12” = ¼) • 1-1/2” = 1’- 0” = 1/8 size • 1” = 1’- 0” = 1/12 size • 3/4” = 1’- 0” = 1/16 size • 1/2” = 1’- 0” = 1/24 size • 3/8” = 1’- 0” = 1/32 size • 1/4” = 1’- 0” = 1/48 size • 1/8” = 1’- 0” = 1/96 size • 3/32” = 1’- 0” = 1/128 size

Introduction to Geometric Construction Strict interpretation of geometric construction allows use of only the compass and an instrument for drawing straight lines. In technical drawing, the principles of geometry are employed constantly. GEOMETRIC NOMENICLATURE A. POINTS IN SPACE A point is an exact location in space or on a drawing surface. A point is actually represented on the drawing by a crisscross at its exact location.

B.LINE Lines are straight elements that have no width, but are infinite in length (magnitude), and they can be located by two points which are not on the same spot but fall along the line. Lines may be straight lines or curved lines. A straight line is the shortest distance between two points. It can be drawn in any direction.

Straight lines and curved lines are considered parallel if the shortest distance between them remains constant. The symbol used for parallel line is //. Lines, which are tangent and at 90 degrees are considered perpendicular. The symbol for perpendicular line is . C.ANGLES An angle is formed by the intersection of two lines. There are three major kinds of angles: right angels, acute angles and obtuse angles. The right angle is an angle of 90, an acute angle is an angle less than 90, and an obtuse angle is an angle more than 90. A straight line is 180. The symbol for an angle is < (singular) and...