Dr.R. GANESAMOORTHY.B.E.,M.E.,Ph.d. Professor –Mechanical Engineering Saveetha Engineering College TandalamChennai. 12-Sep-181Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS

Definition Engineering graphics is the language for Effective Communication among engineers which elaborates the details of any component, structure or circuit at its initial drawing through drawing. 12-Sep-182Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS

DRAFTING TOOLS  Drawing Board  Mini drafter or T- square  Drawing Instrument box  Drawing Pencils  Eraser  Templates  Set squares  Protractor  Scale Set  French curves  Drawing clips  Duster piece of cloth(or) brush  Sand-paper (or) Emery sheet block  Drawing sheet 12-Sep-183Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS The following are the various drafting tools used in engineering graphics.

DRAFTING TOOLS 12-Sep-18Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS4

12-Sep-18Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS5 Drawing Sheet DesignationDimension, mm A0841 x 1189 A1594 x 841 A2420 x 594 A3297 x 420 A4210 x 297

Lines Visible Outlines, Visible,Edges- Continuous wide lines Dimension Lines - Continuous narrow Lines Extension Lines - Continuous narrow Lines Construction Lines - Continuous narrow Lines Hatching / Section Lines - Continuous narrow Lines Guide Lines - Continuous narrow Lines Break Lines - Continuous Narrow Freehand Lines Break Lines - Continuous Narrow Lines With Zigzags Dashed Narrow Lines - Dashed Narrow Lines Centre Lines - Long-Dashed Dotted Narrow Lines Cutting Plane Lines - long-dashed dotted narrow line Border Lines - Continuous wide lines 12-Sep-18Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS6

Types of Lines and their applications 1.Continuous narrow line-Dimension lines, Extension lines, Leader lines, Reference lines, Short centre lines, Projection lines, Hatching, Construction lines, Guide lines, Outlines of revolved sections,Imaginary lines of intersection 2.Continuous narrow freehand line-Preferably manually represented termination of partial or interrupted views, Cuts and sections, if the limit is not a line of symmetry or a Centre line· 12-Sep-18Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS7

Types of Lines and their applications Conti Continuous narrow line with zigzags -Preferably mechanically represented termination of partial or interrupted views. cuts and sections, if the limit is not a line of symmetry or a centre line. 4.Continuous wide line -Visible edges, visible outlines, Main representations in diagrams, maps. flow charts. 5.Dashed narrow line -Hidden edges,Hidden outlines 12-Sep-18Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS8

Types of Lines and their applications Conti Long-dashed dotted narrow line -Centre lines / Axes. Lines of symmetry, Cutting planes 7. Long-dashed dotted wide line-Cutting planes at the ends and changes of direction outlines of visible parts situated front of cutting plane 12-Sep-18Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS9

Dimensioning Dimensioning provided through the distances between the surfaces, location of holes, nature of surface finish, type of material, etc. Elements of dimensioning 1.Dimension line 2.Leader line 3.Origin indication 4.Dimension 5.Projection or extension line 6. Dimension line termination 12-Sep-18Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS10

Principles of Dimensioning I. All dimensional information necessary to describe a component clearly and completely shall be written directly on a drawing. 2. Each feature shall be dimensioned once only on a drawing, i.e., dimension marked in one view need not be repeated in another view. 12-Sep-18Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS11

Principles of Dimensioning Conti Dimension should be placed on the view where the shape is best seen (Fig.) 4. As far as possible, dimensions should be expressed in one unit only preferably in millimetres, without showing the unit symbol (mm). 12-Sep-18Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS12

Principles of Dimensioning Conti As far as possible dimensions should be placed outside the view (Fig.). 6. Dimensions should be taken from visible outlines rather than from hidden lines (Fig.) 12-Sep-18Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS13

Principles of Dimensioning Conti No gap should be left between the feature and the start of the extension line(Fig.). 8. Crossing of centre lines should be done by a long dash and not a short dash (Fig.). 12-Sep-18Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS14

Methods of Indicating Dimensions Method - 1 (Aligned method). Method - 2 (Uni -directional method) 12-Sep-18Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS15

Arrangement of Dimensions They are arranged in three ways. 1. Chain dimensioning 2. Parallel dimensioning 3. Combined dimensioning. 12-Sep-18Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS16

12-Sep-18Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS17 Set of Scales Scales are used to make drawing of the objects to proportionate size desired. These are made of wood, steel or plastic. 12-Sep-18Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS17 M1M2M3M4M5M6M7M8 Scale on one edge1:11:251:101:501:2001:3001:4001:1000 Scale on other edge 1:21:51:201:1001:5001:6001:8001:2000 Scales for use on technical drawings(IS: ) CategoryCategory Recommended scales Enlargeme nt scales 50 : 1 5 : 1 20 : 1 2 : 1 10 : 1 Full size 1 : 1 Reduction scales 1 : 2 1 : 20 1 : : : 5 1 : 50 1 : : : 10 1 : : : 10000

Scale Definition : Scale is defined as the ratio of the linear dimension of an element of an object as represented in the original drawing to the linear dimension of the same element of the object itself. Full size scale If we show the actual length of an object on a drawing, then the scale used is called full size scale. 12-Sep-18Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS18

Scale Conti ….. Reducing scale If we reduce the actual length of an object so as to accommodate that object on drawing, then scale used is called reducing scale. Enlarging scale Drawings of smaller machine parts, mechanical instruments, watches, etc. are made larger than their real size. These are said to be drawn in an increasing or enlarging scale. 12-Sep-18Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS19

Representative Fraction (R.F) The ratio of the drawing of an object to its actual size is Called the representative fraction, usually referred to as R.F. R.F=Drawing of an object/It’s actual size(in same units) For reducing scale, the drawings will have R.F. values of Less than unity. if 1 cm on drawing represents 1 m length of an object. 12-Sep-18Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS20

Representative Fraction (R.F) conti.... Increasing or enlarging scale, the R.F values will be Greater than unity. For example, when 1 mm length of an object is shown by a length of 1cm on the drawing 12-Sep-18Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS21

Types of Scales 1.Simple scales 2. Diagonal scales 3. Vernier scales Simple scales A plain scale is simply a line, which is divided into a suitable number of equal parts, the first of which is further sub-divided into small parts. It is used to represent either two units or a unit and its fraction such as km, m and dm, etc. 12-Sep-18Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS22

Types of Scales Conti..... Plain scales, Diagonal Scales, Vernier Scale Plain scales are used to read lengths in two units such as metres and decimetres or to read the accuracy correct to first decimal. Diagonal scales are used to represent either three units of measurements such as metres, decimetres, centimetres or to read to the accuracy correct to two decimals. The diagonal scales, vernier scales are used to read very Small units with accuracy. They are used, when a diagonal Scale is inconvenient to use due to lack of space. 12-Sep-18Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS23

Types of Scales Conti..... Vernier scale A vernier Scale consists of two parts, i.e., Main scale and a vernier. The main scale is a Plain scale divided into minor divisions. The vernier is also a scale used along with the main scale to read the third unit, which is the fraction of the second unit on the main scale. 12-Sep-18Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS24

Types of Scales Conti..... Least count: Least count the smallest distance that can be measured accurately by the vernier scale and is the vernier scale and is the difference between a main scale division and a vernier scale division. Types of Verniers: 1.Forward vernier or direct vernier 2.Backward vernier or retrograde vernier 12-Sep-18Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS25

Lettering Technical lettering is the process of forming letters, numerals, and other characters in technical drawing. It is used to describe, or provide detailed specifications for, an object. 12-Sep-18Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS26 CharacteristicParameterRatioDimensions(mm) Lettering Height (Height of capitals) h(14/14)h Height of lower case letters (without stem or tail) c(10/14)h Spacing between characters a(2/14)h Minimum spacing of base characters b(20/14)h Minimum spacing between words e(6/14)h Thickness of linesd(1/14)h

Lettering Conti..... CharacteristicParameterRatioDimensions(mm) Lettering Height (Height of capitals) h(10/10)h Height of lower case letters (without stem or tail) c(7/10)h Spacing between characters a(2/10)h Minimum spacing of base characters b(14/10)h Minimum spacing between words e(6/10)h Thickness of linesd(1/10)h Sep-18Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS27

Geometric Construction Drawing consists of construction of primitive geometric forms viz. points, lines and planes that serve at building blocks. The use of lines for obtaining the drawing of planes 12-Sep-18Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS28

Geometric Construction Conti Solids are obtained by combination of planes. Plane surfaces of simple solids are shown in figure. 12-Sep-18Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS29

To divide a straight line into a given number of equal parts say 5. Construction 12-Sep-18Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS30 1. Draw AC at any angle θ to AB. 2. Construct the required number of equal parts of convenient length on AC like 1,2,3. 3. Join the last point 5 to B 4. Through 4, 3, 2, 1 draw lines parallel to 5B to intersect AB at 4',3',2' and 1'.

12-Sep-18Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS31 1. Draw a line AB and AC making the given angle. 2. With centre A and any convenient radius R draw an arc intersecting the sides at D and E. 3. With centers D and E and radius larger than half the chord length DE, draw arcs intersecting at F 4. Join AF, <BAF = <PAC. To bisect a given angle Construction

To inscribe a square in a given circle Construction 1. With centre 0, draw a circle of diameter D. 2. Through the centre 0, draw two diameters, say AC and BD at right angle to each other. 3. Join A-B, B-C, C- D, and D-A. ABCD is the required square. 12-Sep-18Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS32

To inscribe a hexagon in a given circle. By using a set-square or mini-draughter 1. With centre 0 and radius R draw the given circle. 2. Draw any diameter AD to the circle. 3. Using 30° - 60° set-square and through the point A draw lines AI, A2 at an angle 60° with AD, intersecting the circle at B and F respectively. 4. Using 30° - 60° and through the point D draw lines Dl, D2 at an angle 60° with DA, intersecting the circle at C and E respectively. By joining A, B, C, D, E, F, and A the required hexagon is obtained. 12-Sep-18Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS33

To inscribe a hexagon in a given circle. By using compass 1. With centre 0 and radius R draw the given circle. 2. Draw any diameter AD to the circle. 3. With centres A and D and radius equal to the radius of the circle draw arcs intersecting the circles at B, F, C and E respectively. 4. ABC D E F is the required hexagon. 12-Sep-18Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS34

To circumscribe a hexagon on a given circle of radius R construction 1. With centre 0 and radius R draw the given circle. 2. Using 60° position of the mini draughter or set square, circumscribe the hexagon as shown. 12-Sep-18Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS35

To construct a hexagon, given the length of the side (a)Using set square 1. Draw a line AB equal to the side of the hexagon. 2. Using 30° - 60° set-square draw lines AI, A2, and BI,B2. 3. Through 0, the point of intersection between the lines A2 at D and B2 at E. 4. Join D,E 5. ABC D E F is the required hexagon. 12-Sep-18Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS36

To construct a hexagon, given the length of the side (b) By using compass 1. Draw a line AB equal to the of side of the hexagon. 2. with centres A and B and radius AB, draw arcs intersecting at 0, the centre of the hexagon. 3. With centres 0 and B and radius OB (=AB) draw arcs intersecting at C. 4. Obtain points D, E and F in a similar manner. 12-Sep-18Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS37

To construct a regular polygon (say a pentagon) given the length of the side. 1. Draw a line AB equal to the side and extend to P such that AB = BP 2. Draw a semicircle on AP and divide it into 5 equal parts by trial and error. 3. Join B to second division 4. Irrespective of the number of sides of the polygon B is always joined to the second division. 5. Draw the perpendicular bisectors of AB and B2 to intersect at O. 6. Draw a circle with 0 as centre and OB as radius. 7. With AB as radius intersect the circle successively at D and E.Then join CD. DE and EA. 12-Sep-18Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS38

To construct a regular polygon (say a hexagon) given the side AB – alternate Method. 1. Steps 1 to 3 are same as above 2. Join B- 3, B-4, B-5 and produce them. 3. With 2 as centre and radius AB intersect the line B, 3 produced at D. Similarly get the point E and F. 4. Join 2- D, D-E, E-F and F-A to get the required hexagon. 12-Sep-18Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS39

To construct a pentagon, given the length of side. 1. Draw a line AB equal to the given length of side. 2. Bisect AB at P. 3. Draw a line BQ equal to AB in length and perpendicular to AB. 4. With centre P and radius PQ, draw an arc intersecting AB produced at R. AR is equal to the diagonal length of the pentagon. 5. With centres A and B and radii AR and AB respectively draw arcs intersecting at C. 6. With centres A and B and radius AR draw arcs intersecting at D. 7. With centres A and B and radii AB and AR respectively draw arcs intersecting at E. ABCDE is the required pentagon. 12-Sep-18Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS40

By included angle method 1.Draw a line AB equal to the length of the given side. 2.Draw a line B 1 such that <AB 1 = 108° (included angle) 3.Mark C on B1 such that BC = AB 4.Repeat steps 2 and 3 and complete the pentagon ABCDE 12-Sep-18Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS41 To construct a pentagon, given the length of side.