Engineering graphics introduction converted

introduction of engineering graphics ,projection of points,lines,planes,solids,section of solids,development of surfaces,isometric projection,perspective projection

1. Dr.R. GANESAMOORTHY.B.E.,M.E.,Ph.d.
Professor –Mechanical Engineering
SaveethaEngineering College
Tandalam
Chennai.
24-Sep-18 1Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS

2. Definition
Engineeringgraphicsisthelanguagefor
EffectiveCommunicationamongengineerswhich
elaboratesthedetailsofanycomponent,
structureorcircuitatitsinitialdrawingthrough
drawing.
24-Sep-18 2Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS

3. 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
24-Sep-18 3Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS
The following are the various drafting tools used in
engineering graphics.

4. DRAFTING TOOLS
24-Sep-18 Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS 4

5. 24-Sep-18 Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS 5
Drawing Sheet
Designatio
n
Dimension, mm
A0 841 x 1189
A1 594 x 841
A2 420 x 594
A3 297 x 420
A4 210 x 297

6. 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
24-Sep-18 Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS 6

7. Types of Lines and their applications
1.Continuousnarrowline-Dimensionlines,Extension
lines,Leaderlines,Referencelines,Shortcentrelines,
Projectionlines,Hatching,Constructionlines,Guidelines,
Outlinesofrevolvedsections,Imaginarylinesof
intersection
2.Continuousnarrowfreehandline-Preferablymanually
representedterminationofpartialorinterruptedviews,
Cutsandsections,ifthelimitisnotalineofsymmetryor
aCentreline·
24-Sep-18 Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS 7

8. Types of Lines and their applications
Conti........
3.Continuousnarrowlinewithzigzags-Preferably
mechanicallyrepresentedterminationofpartialor
interruptedviews.cutsandsections,ifthelimitisnota
line of symmetry or a centre line .
4.Continuous wide line -Visible edges, visible outlines,
Main representations in diagrams, maps. flow charts.
5.Dashednarrowline-Hiddenedges,Hiddenoutlines
24-Sep-18 Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS 8

9. Types of Lines and their applications
Conti........
6.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
24-Sep-18 Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS 9

10. 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
24-Sep-18 Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS 10

11. 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.
24-Sep-18 Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS 11

12. Principles of Dimensioning
Conti.....
3. 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).
24-Sep-18 Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS 12

13. Principles of Dimensioning
Conti.....
5. 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.)
24-Sep-18 Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS 13

14. Principles of Dimensioning
Conti.....
7. 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.).
24-Sep-18 Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS 14

15. Methods of Indicating Dimensions
Method -1 (Aligned method).
Method -2 (Uni -directional method)
24-Sep-18 Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS 15

16. Arrangement of Dimensions
They are arranged in three ways.
1. Chain dimensioning 2. Parallel dimensioning
3. Combined dimensioning.
24-Sep-18 Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS 16

17. 24-Sep-18 Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS 17
Set of Scales
Scales are used to make drawing of the objects to
proportionate size desired. These are made of wood,
steel or plastic.
24-Sep-18 Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS 17
M1 M2M3 M4 M5 M6 M7M8
Scaleonone
edge
1:1 1:251:101:50 1:2001:3001:4001:1000
Scaleonother
edge
1:2 1:51:201:1001:5001:6001:8001:2000
Scalesforuseontechnicaldrawings(IS:46-
1988)
CategoryCategoryRecommendedscales
Enlargeme
ntscales
50 : 1
5 : 1
20 : 1
2 : 1
10 : 1
Full size 1 : 1
Reduction
scales
1 : 2
1 : 20
1 : 200
1 : 2000
1 : 5
1 : 50
1 : 500
1 : 5000
1 : 10
1 : 100
1 : 1000
1 : 10000

18. Scale
Definition:
Scaleisdefinedastheratioofthelineardimensionof
anelementofanobjectasrepresentedintheoriginal
drawingtothelineardimensionofthesameelementof
theobjectitself.
Fullsizescale
Ifweshowtheactuallengthofanobjectonadrawing,
thenthescaleusediscalledfullsizescale.
24-Sep-18 Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS 18

19. 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.
24-Sep-18 Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS 19

20. RepresentativeFraction(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.
24-Sep-18 Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS 20

21. RepresentativeFraction(R.F) conti....
Increasingorenlargingscale,theR.Fvalueswillbe
Greaterthanunity.
Forexample,when1mmlengthofanobjectisshownby
alengthof1cmonthedrawing
24-Sep-18 Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS 21

22. Types of Scales
TypesofScales
1.Simplescales
2.Diagonalscales
3.Vernierscales
Simplescales
Aplainscaleissimplyaline,whichisdividedintoa
suitablenumberofequalparts,thefirstofwhichisfurther
sub-dividedintosmallparts.
Itisusedtorepresenteithertwounitsoraunitandits
fractionsuchaskm,manddm,etc.
24-Sep-18 Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS 22

23. Types of Scales Conti.....
Plain scales , Diagonal Scales, VernierScale
Plain scales are used to read lengths in two units such as
metres and decimetresor 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, vernierscales 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.
24-Sep-18 Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS 23

24. Types of Scales Conti.....
Vernierscale
AvernierScaleconsistsoftwoparts,i.e.,Mainscale
andavernier.
ThemainscaleisaPlainscaledividedintominor
divisions.
Thevernierisalsoascaleusedalongwiththemain
scaletoreadthethirdunit,whichisthefractionof
thesecondunitonthemainscale.
24-Sep-18 Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS 24

25. 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
24-Sep-18 Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS 25

26. 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.
24-Sep-18 Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS 26
Characteristic ParameterRatio Dimensions(mm)
Lettering Height
(Height of capitals)
h (14/14)h2.53.557101420
Height of lower case
letters
(without stem or tail)
c (10/14)h-2.53.55 71014
Spacing between
characters
a (2/14)h0.350.50.711.422.8
Minimum spacing of base
characters
b (20/14)h3.55710142028
Minimum spacing
between words
e (6/14)h1.051.52.134.268.4
Thickness of lines d (1/14)h0.180.250.350.50.711.4

27. Lettering Conti.....
Characteristic ParameterRatio Dimensions(mm)
Lettering Height
(Height of capitals)
h (10/10)h2.53.557101420
Height of lower case letters
(without stem or tail)
c (7/10)h-2.53.5571014
Spacing between
characters
a (2/10)h0.50.711.422.84
Minimum spacing of base
characters
b (14/10)h3.55710142028
Minimum spacing between
words
e (6/10)h1.52.134.268.412
Thickness of lines d (1/10)h0.250.350.50.711.42
24-Sep-18 Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS 27

28. 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
24-Sep-18 Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS 28

29. Geometric Construction Conti........
Solids are obtained by combination of planes. Plane
surfaces of simple solids are shown in figure.
24-Sep-18 Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS 29

30. To divide a straight line into a given
number of equal parts say 5. Construction
24-Sep-18 Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS 30
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'.

31. 24-Sep-18 Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS 31
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

32. 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.
24-Sep-18 Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS 32

33. 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.
24-Sep-18 Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS 33

34. 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.
24-Sep-18 Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS 34

35. 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 30
0
-
60
0
set square, circumscribe the hexagon as shown.
24-Sep-18 Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS 35

36. 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.
24-Sep-18 Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS 36

37. 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.
24-Sep-18 Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS 37

38. 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.
24-Sep-18 Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS 38

39. 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.
24-Sep-18 Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS 39

40. 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.
24-Sep-18 Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS 40

41. 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
24-Sep-18 Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS 41
To construct a pentagon, given the
length of side.