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MALLA REDDY COLLEGE OF ENGINEERING & TECHNOLOGY
(Autonomous Institution – UGC, Govt. of India)
Recognized under 2(f) and 12 (B) of UGC ACT 1956 (Affiliated to JNTUH, Hyderabad, Approved by AICTE-Accredited by NBA & NACC-‘A’ Grade – ISO 9001:2015 Certified) Maisammaguda, Dhulapally (Post Via. Hakimpet), Secunderabad -500100, Telangana State, India
ENGINEERING DRAWING PRACTICE MANUAL
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Acknowledgements
Although it is impossible to mention everyone, as there are
many people in the department of Mechanical Engineering
takes the honor to thank.
First and foremost we must thank our Principal Dr. V.S.K.
Reddy, for providing his constant support and
encouragement, to complete Mechanical Engineering
department’s First task.
We owe a great deal to the Mechanical Engineering
department faculty members to all the reviewers who
patiently read each page of every chapter of the current
version of Engineering Drawing Practice Manual for the
benefit of 1st^ year B.Tech, MRCET students.
We are thankful to our parents for their blessings.
We welcome any comments concerning the book in spite of
our diligent efforts there may still be room for improvement.
Once again we take the immense pleasure to thank one and
all for their efforts.
HOD
Department of Mechanical Engineering
MRCET, Secunderabad- 14
UNIT – 1
INTRODUCTION TO ENGINEERING DRAWING
Engineering drawing is a two dimensional representation of three dimensional objects. In general, it provides necessary information about the shape, size, surface quality, material, manufacturing process, etc., of the object. It is the graphic language from which a trained person can visualize objects.
Drawing Instruments and aids:
The Instruments and other aids used in drafting work are listed below: Drawing board Set squares French curves Templates Mini drafter Instrument box Protractor Set of scales Drawing sheets Pencils
Drawing Board:
Until recently drawing boards used are made of well seasoned softwood of about 25 mm thick with a working edge for T-square. Nowadays mini-drafters are used instead of T-squares which can be fixed on any board. The standard size of board depends on the size of drawing sheet size required.
Mini-Drafter:
Mini-drafter consists of an angle formed by two arms with scales marked and rigidly hinged to each other .It combines the functions of T-square, set-squares, scales and protractor. It is used for drawing horizontal, vertical and inclined lines, parallel and perpendicular lines and for measuring lines and angles.
Instrument Box
Instrument box contains 1. Compasses, 2. Dividers and 3. Inking pens. What is important is the position of the pencil lead with respect to the tip of the compass. It should be at least 1 mm above as shown in the fig. because the tip goes into the board for grip by 1 mm.
Figure.1. Pencils:
Pencils with leads of different degrees of hardness or grades are available in the market. The hardness or softness of the lead is indicated by 3H, 2H, H, HB, B, 2B, 3B, etc. The grade HB denotes medium hardness of lead used for general purpose. The hardness increases as the value of the numeral before the letter H increases. The lead becomes softer, as the value of the numeral before B increases.
HB Soft grade for Border lines, lettering and free sketching H Medium grade for Visible outlines, visible edges and boundary lines 2H Hard grade for construction lines, Dimension lines, Leader lines, Extension lines, Centre lines, Hatching lines and Hidden lines.
Drawing Sheet:
The standard drawing sheet sizes are arrived at on the basic Principal of x: y = 1: 2^ (1/2) and xy = 1 where x and y are the sides of the sheet. For example AO, having a surface area of 1 Sq.m; x = 841 mm and y = 1189 mm. The successive sizes are obtained by either by halving along the length or doubling the width, the area being in the ratio 1: 2. Designation of sizes is given in the fig. For class work use of A2 size drawing sheet is preferred.
Table.1.1 Figure .1.
Guide Lines (Continuous Narrow Lines): These are drawn for lettering and should not be erased after lettering. Break Lines (Continuous Narrow Freehand Lines): Wavy continuous narrow line drawn freehand is used to represent break of an object. Break Lines (Continuous Narrow Lines With Zigzags): Straight continuous narrow line with zigzags is used to represent break of an object. Dashed Narrow Lines (Dashed Narrow Lines): Hidden edges / Hidden outlines of objects are shown by dashed lines of short dashes of equal lengths of about 3 mm, spaced at equal distances of about 1 mm. the points of intersection of these lines with the outlines / another hidden line should be clearly shown. Center Lines (Long-Dashed Dotted Narrow Lines): These are draWn at the center of the drawings symmetrical about an axis or both the axes. These are extended by a short distance beyond the outline of the drawing. Cutting Plane Lines: Cutting Plane Line is drawn to show the location of a cutting plane. It is long-dashed dotted narrow line, made wide at the ends, bends and change of direction. The direction of viewing is shown by means of arrows resting on the cutting plane line. Border Lines: Border Lines are continuous wide lines of minimum thickness 0.7 mm.
Table.1.
CONVENTIONAL REPRESENTATION OF MATERIALS
Table.1.
Table.1.
Dimensioning:
Drawing of a component, in addition to providing complete shape description, must also furnish Information regarding the size description. These are provided through the distances between the Surfaces, location of holes, nature of surface finish, type of material, etc. The expression of these Features on a drawing, using lines, symbols, figures and notes is called dimensioning.
Figure.1.
Methods of Indicating Dimensions:
The dimensions are indicated on the drawings according to one of the following two methods.
Method - 1 (Aligned method):
Dimensions should be placed parallel to and above their dimension lines and preferably at the middle, and clear of the line. Dimensions may be written so that they can be read from the bottom or from the right side of the drawing. Dimensions on oblique dimension lines should be oriented as shown in Fig.2.26a and except where unavoidable, they shall not be placed in the 30° zone. Angular dimensions are oriented.
Figure.1.6(a)
Figure.1.6 (b)
Method - 2 (Uni-directional):
Dimensions should be indicated so that they can be read from the bottom of the drawing only. Non- horizontal dimension lines are interrupted, preferably in the middle for insertion of the dimension. Note: Horizontal dimensional lines are not broken to place the dimension in both cases.
Figure.1.
- Join A-D which is the length of the side of the required polygon.
- Set the compass to the length AD and starting from D mark off on the circumference of the circles, obtaining the points E,F, etc. The figure obtained by joining the points A,D,E etc., is the required polygon.
Figure.1.
3. To inscribe a hexagon in a given circle.
Figure.1. Construction :
- With centre O and radius R draw the given circle.
- Draw any diameter AD to the circle.
- Using 30° - 60° set-square and through the point A draw lines A1, A2 at an angle 60° with AD, intersecting the circle at B and F respectively.
- Using 30°-60° set-square 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,S the required hexagon is obtained. 4. To construct a regular polygon (say a pentagon) given the length of the side.
Construction:
- Draw a line AB equal to the side and extend to P such that AB = BP
- Draw a semicircle on AP and divide it into 5 equal parts by trial and error.
- Join B to second division Irrespective of the number of sides of the polygon B is always joined to the second division.
- Draw the perpendicular bisectors of AB and B2 to intersect at O.
- Draw a circle with O as centre and OB as radius.
- With AB as radius intersect the circle successively at D and E. Then join CD, DE and EA.
Figure.1.
5. To construct a regular polygon (say a hexagon) given the side AB.
Construction:
- Draw a line AB equal to the side and extend to P such that AB = BP
- Draw a semicircle on AP and divide it into 6 equal parts by trial and error.
- Join B to second division
- Join B- 3, B-4, B-5 and produce them.
- With 2 as centre and radius AB intersect the line B, 3 produced at D. Similarly get the point E and F.
- Join 2- D, D-E, E-F and F-A to get the required hexagon.
D
Figure.1.
7. To construct a regular figure of given side length and of N sides on a straight line.
Construction:
- Draw the given straight line AB.
CONIC SECTIONS
Cone is formed when a right angled triangle with an apex and angle 𝜃 is rotated about its altitude as the axis. The length or height of the cone is equal to the altitude of the triangle and the radius of the base of the cone is equal to the base of the triangle. The apex angle of the cone is 2𝜃. When a cone is cut by a plane, the curve formed along the section is known as a conic.
a) CIRCLE:
When a cone is cut by a section plane A-A making an angle 𝛼 = 90° with the axis, the section obtained is a circle.
b) ELLIPSE:
When a cone is cut by a section plane B-B at an angle, 𝛼 more than half of the apex angle i.e., 𝜃 and less than 90°, the curve of the section is an ellipse. Its size depends on the angle 𝛼 and the distance of the section plane from the apex of the cone.
c) PARABOLA:
If the angle 𝛼 is equal to 𝜃 i.e., when the section plane C-C is parallel to the slant side of the cone the curve at the section is a parabola. This is not a closed figure like circle or ellipse. The size of the parabola depends upon the distance of the section plane from the slant side of the cone.
d) HYPERBOLA:
If the angle 𝛼 is less than 𝜃 (section plane D-D), the curve at the section is hyperbola. The curve of intersection is hyperbola, even if 𝛼 = 𝜃 , provided the section plane is not passing through the apex of the cone. However if the section plane passes through the apex, the section produced is an isosceles triangle.
Figure.1.
Eccentricity(e) :
a. If e=1, it is parabola b. If e>1, it is hyperbola c. If e<1, it is an ellipse
Where eccentricity e is the ratio of distance of the point from the focus to the distance of the point from the directrix.
PARABOLA:
In physical world, parabola are found in the main cables on simple suspension bridge, as parabolic reflectors in satellite dish antennas, vertical curves in roads, trajectory of a body, automobile head light, parabolic receivers.
Figure.1.
ELLIPSE:
Ellipses are mostly found as harmonic oscillators, phase visualization, elliptical gears, ellipse wings.
Figure.1.
To draw an ellipse with the distance of the focus from the directrix at 50mm and eccentricity = 2/3 (Eccentricity method)
Construction :
- Draw any vertical line CD as directrix.
- At any point A in it, draw the axis.
- Mark a focus F on the axis such that AF1=50mm.
- Divide AF1 in to 5 equal divisions.
- Mark the vertex V on the third division-point from A.
- Thus eccentricity e= VF1/VA = 2/3.
- A scale may now be constructed on the axis which will directly give the distances in the required ratio.
- At V, draw a perpendicular VE = VF1. Draw a line joining A and E.
- Mark any point 1 on the axis and through it draw a perpendicular to meet AE produced at 1'.
- With centre F and radius equal to 1-1', draw arcs to intersect a perpendicular through 1 at points P1 and P'1.
- Similarly mark points 2, 3 etc. on the axis and obtain points P2 and P'2, P3 and P'3, etc.
- Draw the ellipse through these points, it is a closed curve two foci and two directrices.
Figure.1.
HYPERBOLA
Lampshades, gear transmission, cooling towers of nuclear reactors are some of the applications of Hyperbola.
Figure.1.
To draw a hyperbola with the distance of the focus from the directrix at 50mm and e=3/ (Eccentricity method)
Figure.1. Construction :
- Draw the directrix CD and the axis AB.
- Mark the focus F on AB and 65mm from A.
- Divide AF into 5 equal divisions and mark V the vertex, on the second division from A.
- Draw a line VE perpendicular to AB such that VE=VF. Join A and E.
- Mark any point 1 on the axis and through it, draw a perpendicular to meet AE produced at 1'.
- With centre F and radius equal to 1-1', draw arcs intersecting the perpendicular through 1 at P and P'1.
- Similarly mark a number of points 2, 3 etc and obtain points P2 and P'2, etc.
