enotes au 305 mdd unit1 vikas verma.pdf

8/10/2019 ENotes AU 305 MDD Unit1 Vikas Verma.pdf

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UNIT1

Drawing Conventions

Unit-01/Lecture-01

Drawing and dimensioning IS codes:

In all the three types of exchange like exchange of goods, exchange of services and exchange of

information, technical drawings form an essential component.

Exchange of goods of technical nature in national and international trade nearly always need to be

accompanied by service diagrams, or other technical drawings illustrating the components, their

assembly and their use.

Exchange of services may involve, for example, consultancy work or the design of an assembly in one

unit for construction in another. In such cases, the technical drawing is an important way of

communicating instructions or advice.

In exchange of information, especially where different languages are involved, the technical drawings

can clarify ambiguities or help to resolve problems in communicating by spoken or written word across

languages barriers.

To achieve these objectives, IS 696 Code of practice for general engineering drawings was originallyissued in 1955 and revised twice in 1960 and 1972. Since the publication of the said standard,

considerable progress has been achieved in the field of standardization of engineering drawing by

mutual agreement between various countries and has taken the shape of firm standard. The growing

international cooperation, introduction of Foreign technology or export of technology has necessitated

to develop internationally unified method and symbols for indicating in engineering drawing.

To meet the above necessity, the contents of IS 696:1972 Code of practice for general engineering

drawings (second revision) have been harmonized with the relevant subject matter of 1S0 technical

drawings and published a series of standards on technical drawing. IS 696 was so long being used by the

students of technical institutions as a guide in engineering drawing. The technical committee

responsible felt the need to bring out a special publication containing relevant information in the field of

drawing standard in one document to meet the requirements of the students. Accordingly, a specialpublication SP 46:1988 Engineering drawing practice for schools and colleges was brought out in the

year 1988. This publication also includes geometrical tolerance, guide for selection of fits in addition to

the general principles and convention of engineering drawing to make the publication more informative.

Since then, lot of changes have taken place in the International and Indian Standards. This revised

edition incorporates all the changes applicable to Engineering drawings till the beginning of the year

2001.

IS 696-1972 (withdrawn). Now refer SP 46: 1988 Engineering Drawing Practice for school colleges.

Lettering 9609: 1990

Sectional views and sectioning:

Sectional views, commonly called sections, are used to show interior detail that is too complicated to be

shown clearly and dimensioned by the traditional orthographic views and hidden lines. A sectional view

is obtained making an imaginary cut through the part, and by drawing the features on the cut surface, as

shown in Figure 18. In a drawing, the exposed or cut surfaces are identified by section lining, or

crosshatching. Section views show internal part detail as solid lines instead of hidden lines, which

improve communication. Hidden lines and details

behind the cutting-plane line are usually omitted unless they are required for clarity. A sectional view

can sometimes replace one of the regular views, for example, a regular front view as shown in Figure.


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RGPV Examination/June-2011

Full Sections

When the cutting plane extends entirely through the object in a straight line and the front half of the

object is theoretically removed, a full section is obtained, Figure 23 (B). This type of section is used for

both detail and assembly drawings. When the cutting plane divides the object into two identical parts, it

is not necessary to indicate its location. However, the cutting plane may be identified and indicated in

the usual manner to increase clarity.


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Half Sections

A symmetrical object or assembly may be drawn as a half section, Figure 24 (C), showing one half up to

the center line in section and the other half in full view. A normal centerline is listed on the section view.

The wording, half section, can be confusing because one thinks of showing half the part. Remember, a

half section shows one-fourth of the part, not one-half.


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The half section drawing is not normally used where the dimensioning of internal diameters is required.

This is because many hidden lines would have to be added to the portion showing the external features.

This type of section is used mostly for assembly drawings where internal and external features are

clearly shown and only overall and center-to-center dimensions are required.

S.NO RGPV QUESTIONS Year Marks

Q.1 Explain the following sectional views: Full Section, Half

section , Revolved section, Removed section.

June-2011 20


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Unit-01/Lecture-02

Offset Sections

In order to include features that are not in a straight line, the cutting-plane line may be offset or bent, so

as to include several planes or curved surfaces, Figure 25. An offset section is similar to a full section in

that the cutting plane extends through the object from one side to the other. The change in direction of

the cutting-plane line is not shown on the sectional view.

Broken-out Section

When certain internal and external features of an object can be shown without drawing another view,broken-out and partial sections are used, Figure 26. A cutting-plane line or a break line is used to indicate

where the section is taken. The break line is normally a jagged line, which better indicates the break.

Broken-out sections save drawing time and drawing space. Most CAD systems have a freehand sketching

tool to create the break line.


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Aligned Section

A aligned section is not a true projection of the cut surface. It is often used when a part contains webs,

ribs, spokes, or similar features. It revolves or aligns special part features to clarify them or make them

easier to represent in section. One can conceptually think about a aligned section as a specialized offset

section, Figure. The cutting plane can be bent to pass through all of the nonaligned features in the un-

sectioned view. Another example is shown in Figure.


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Revolved Sections

A revolved section is made by revolving the cross-section view 90 degrees about an axis of revolution and

superimposing the section view on the orthographic view. Visible lines adjacent to the revolved view can

be either drawn or broken out using conventional breaks, as shown in Figure 29 (B). When the revolved

view is superimposed on the part, the original lines of the part behind the section are deleted. The cross

section is drawn true shape and size, not distorted to fit the view. The axis of revolution is shown on the

revolved view as a centreline. Another example is shown in Figure 30.

Revolved sections are useful for describing a cross section without having to draw another view. In

addition, these sections are especially helpful when a cross section varies or the shape of the part is not

apparent from the given orthographic views.


Removed Section

A removed section differs from the revolved section in that the section is removed to an open area on the

drawing instead of being drawn directly on the view. Removed sections are used when there is not enough

room on the orthographic view for a revolved section. Removed sections are used to show the contours of

complicated shapes, such as the wings and fuselage of an airplane, blades for jet engines or power plant

turbines, and other parts that have continuously varying shapes. Frequently, the removed section is drawn

to an enlarged scale for clarification and easier dimensioning, Figure 31 and Figure 32 Figure


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S.N

O

RGPV QUESTIONS Year Marks

Q.1 Explain the following sectional views: Full Section, Half

section , Revolved section, Removed section.

June-2011 20


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Unit-01/Lecture-03

Surface finish:

Surface

A surface is a boundary that separates an object from another object or substance. In order to make

understand the measurement of surface finish, surfaces can then further be divided into two more types as

following: Real Surface: It is the actual boundary of an object. It is produced as a result of the process that

created the surface. Measured Surface: A measured surface is a representation of the real surface obtained

with some measuring instrument. This distinction is made, because no measurement will give the exactreal surface. Refer fig. 1 to see the magnified view of a sample surface and the characteristics of a surface.

Surface is made ofRoughness, Waviness and Lay.

(Fig1: Magnified view of surface)

Surface Finish Imperfections:

The subject of surface finish imperfections consists of mainly following two imperfections: Form Error and

Texture. The Form Error is for longer wavelength (Refer Fig. 1) deviations of a surface from the

corresponding nominal surface. Form errors result from large scale problems in the manufacturing process

such as errors in a machine tool ways, guides or spindles, inaccurate alignment of work-piece. Form error is

on the dividing line in size scale between geometric errors and finish errors. We shall be discussing more on

the surface Texture imperfection, as it is indicated in the drawing as surface roughness symbol.

Surface Texture -

Surface texture is the combination of fairly short wavelength deviations of a surface from the nominal

surface. Texture includes roughness, waviness and a lay, that is, all of the deviations that are shorter in

wavelength than form error deviations.

Roughness -

Roughness includes the finest (shortest wavelength) irregularities of a surface. Roughness generally results

from a particular production process or material condition.

Waviness -

Waviness includes the more widely spaced (longer wavelength) deviations of a surface from its nominal

shape. Waviness errors are intermediate in wavelength between roughness and form error. Note, that

distraction between waviness and form error is not always made in practice and it is not always clear how

to make it.


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Lay -

Lay refers to the predominant direction of the surface texture. Ordinarily, lay is determined by the

particular production method and geometry used.

However, in practice, both the words Surface Texture and Surface Roughness are used to explain

common meaning of surface roughness symbols.

Surface roughness heights are generally measured in micro inches or micrometers. A micrometer,

abbreviated , is one millionth of a meter.

The most common and popular method amongst all is interpreting thro average roughness indication. This

is known as Rain which, R stands for Roughness and a stands for average. The other methods are Rz, Rt,

Rmax etc.

RaAverage Roughness

Also known as Arithmetic Average (AA), Center Line Average (CLA), Arithmetical Mean Deviation of the

profile.

The average roughness is the area between the roughness profile and its mean line, or the integral of the

absolute value of the roughness profile height over the evaluation length.

Graphically, the average roughness is the area between the roughness profile and its center line divided by

the evaluation length (normally five sample lengths with each sample length equal to one cutoff).The average roughness is by far the most commonly used parameter in surface finish measurement. The

earliest analog roughness measuring instruments measured only Ra by drawing a stylus continuously back

and forth over a surface and integrating (finding the average) electronically. It is fairly easy to take the

absolute value of a signal and to integrate a signal using only analog electronics. That is the main reason Ra

has such a long history.


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Surface Roughness Values and symbol in drawing

Meaning of complete surface finish symbol is as below:

b = Production method, treatment or coating

c = Sampling length

d = Direction of lay

e = Machining allowance

f = Other roughness value than Ra

a = Roughness value Ra in micrometer or grade number


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Unit-01/Lecture-04

Tolerance:

The permissible variation of a size is called tolerance. It is the difference between the maximum and

minimum permissible limits of the given size. If the variation is provided on one side of the basic size, it is

termed as unilateral tolerance. Similarly, if the variation is provided on both sides of the basic size, it is

known as bilateral tolerance.

Limit

The two extreme permissible sizes between which the actual size is contained are called limits. The

maximum size is called the upper limit and the minimum size is called the lower limit.

Deviation

It is the algebraic difference between a size (actual, maximum, etc.) and the corresponding basic size.

Actual Deviation

It is the algebraic difference between the actual size and the corresponding basic size.

Upper Deviation

It is the algebraic difference between the maximum limit of the size and the corresponding basic size.

Lower Deviation

It is the algebraic difference between the minimum limit of the size and the corresponding basic size.

Allowance

It is the dimensional difference between the maximum material limits of the mating parts, intentionally

provided to obtain the desired class of fit. If the allowance is positive, it will result in minimum clearance

between the mating parts and if the allowance is negative, it will result in maximum interference.

Basic Size

It is determined solely from design calculations. If the strength and stiffness requirements need a 50mm

diameter shaft, then 50mm is the basic shaft size. If it has to fit into a hole, then 50 mm is the basic size of

the hole. F igure 15.1 illustrates the basic size, deviations and tolerances.

Here, the two limit dimensions of the shaft are deviating in the negative direction with respect to the basic

size and those of the hole in the positive direction. The line corresponding to the basic size is called the zero

line or line of zero deviation.

Design Size

It is that size, from which the limits of size are derived by the application of tolerances. If there is no

allowance, the design size is the same as the basic size. If an allowance of 0.05 mm for clearance is applied,

say to a shaft of 50 mm diameter, then its design size is (500.05) = 49.95 mm. A tolerance is then applied

to this dimension.

Actual Size

It is the size obtained after manufacture.


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Unit-01/Lecture-05

CONVENTIONAL REPRESENTATION

Materials

As a variety of materials are used for machine components in engineering applications, it is preferable to

have different conventions of section lining to differentiate between various materials. The

recommended conventions in use are shown in Fig.2.26.

Machine Components

When the drawing of a component in its true projection involves a lot of time, its convention may be

used to represent the actual component. Figure 2.27 shows typical examples of conventional

representation of various machine components used in engineering drawing.


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Q.1 Draw the conventional representation of the Leaf spring

with eye and centre band.

June-2011 5

Q.2


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Unit-01/Lecture-06RGPV Examination/June-2013/Dec-2012/Dec-2011/June-2011


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S.NO RGPV QUESTION YEAR MARKS

Q.1 Draw the conventional representation

of the following. Straight knurling,

Bearing, External thread, Semi elliptical

spring with eye.

June-2013

Dec-2011

14

Q.2 Draw the conventional representation

of the following. Bearing, Splined

shaft, Cylindrical tension spring, Spur

gear

Dec- 2012 7


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Unit 01/Lecture 07

Rivet heads and Riveted joints:

Rivet-

A rivet is a round rod of circular cross-section. It consists of two parts, viz., head and shank (Fig. 10.1 (a)).

Mild steel, wrought iron, copper and aluminium alloys are some of the metals commonly used for rivets.

The choice of a particular metal will depend upon the place of application.

Riveting-

Riveting is the process of forming a riveted joint. For this, a rivet is first placed in the hole drilled through

the two parts to be joined. Then the shank end is made into a rivet head by applying pressure, when it is

either in cold or hot condition. Pressure may be applied to form the second rivet head, either by direct

hammering or through hydraulic or pneumatic means. While forming the rivet head, the shank will bulge

uniformly. Hence, a certain amount of clearance between the hole and shank must be provided before

riveting (Fig. 10.1 (b)).

Hot riveting produces better results when compared to cold riveting. This is because, after hot riveting,

the contraction in the shank length tends to pull the parts together, making a tight joint.

RGPV Examination /Feb-2010

Types of Rivet Head:

Various forms of rivet heads, used in general engineering works and boiler construction and as

recommended by Bureau of Indian Standards, are shown in Fig. 10.3. The standard proportions are also

indicated in the figure.


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Definitions:

The definitions of the terms, associated with riveted joints are given below:

Pitch-

It is the distance between the centres of the adjacent rivets in the same row. It is denoted by p and

usually taken as 3d, where d is the rivet diameter.

Margin-

It is the distance from the edge of the plate to the centre of the nearest rivet. It is usually taken as 1.5d,

where d is the rivet diameter. It is denoted by m.

Chain Reviting-

If the rivets are used along a number of rows such that the rivets in the adjacent rows are placed directly

opposite to each other, it is known as chain riveting (Fig. 10.10).

Zig-Zag Riveting-

In a multi-row riveting, if the rivets in the adjacent rows are staggered and are placed inbetween those of

the previous row, it is known as zig-zag riveting (Fig. 10.11).

Row Pitch-

It is the distance between two adjacent rows of rivets. It is denoted by pr and is given by, pr = 0.8p, for

chain riveting pr = 0.6p, for zig-zag riveting.

Diagonal Pitch-

This term is usually associated with zig-zag riveting and is denoted by pd. It is the distance between the

centre of a rivet in a row to the next rivet in the adjacent row.


Q.1 Explain any five rivet heads with

neat sketch.

June-2011 10


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Unit 01/Lecture 08

Types of Riveted Joint:

Lap Joint

In a lap joint, the plates to be riveted, overlap each other. The plates to be joined are first bevelled at theedges, to an angle of about 80 (Fig. 10.9). Depending upon the number of rows of rivets used in the joint,

lap joints are further classified as single riveted lap joint, double riveted lap joint and so on.

Figure 10.9 shows a single riveted lap joint. The size of the rivet, d is taken as, d = 6 t mm where t is the

thickness of the plates to be joined in millimetres. Figures 10.10 and 10.11 show double riveted chain, lap

joint and double riveted zig-zag lap joint respectively.


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RGPV Examination /Dec-2013/Dec-2012

Butt Joint

In a butt joint, the plates to be joined, butt against each other, with a cover plate or strap, either on one or

both sides of the plates; the latter one being preferred. In this joint, the butting edges of the plates to be

joined are square and the outer edges of the cover plate(s) is(are) bevelled.

These joints are generally used for joining thick plates, and are much stronger than lap joints. Figures 10.12

and 10.13 show single riveted single strap and a single riveted double strap, butt joints respectively.

In a single strap butt joint, the thickness of the strap (cover plate) is given by, t1 = 1.125t If two straps are

used, the thickness of each cover plate is given by, t2 = 0.75t


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Figures 10.14 and 10.15 show double riveted, double strap chain, butt joint and double riveted, double

strap zig-zag butt joint.


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Q.1 Draw double riveted chain lap joint of 18 mm thick plateusing snap headed rivets. Show at least 3 rivets in the plan

and add a sectional view.

Dec 2013 7

Q.2 Draw sectional view from front and view from above of

double riveted zig- zag lap joint of 10 mm thick plate.

Dec-2012 7


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Unit 01/Lecture 09

Types of welded joints and representation.

Welding is an effective method of making permanent joints between two or more metal parts. Cast iron,

steel and its alloys, brass and copper are the metals that may be welded easily. Production of leak proof

joints that can withstand high pressures and temperatures are made possible with advanced welding

technology. For this reason, welding is fast replacing casting and forging wherever possible. Whencompared to riveting, welding is cheaper, stronger and simpler to execute at site with considerable freedom

in design. Hence, it is widely used in ship building and structural fabrication in place of riveting.

Basic terms of a welded joint are shown in Fig. 11.1 and the five basic types of joints are shown

in Fig. 11.2.

Various categories of welded joints (welds) are characterized by symbols which, in general

are similar to the shape of welds to be made. These symbols are categorised as:

(i) Elementary symbols (Table 11.1),

(ii) Supplementary symbols (Table 11.2),

(iii) Combination of elementary and supplementary symbols (Table 11.3) and

(iv) Combination of elementary symbols (Table 11.4).


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RGPV Examination /Dec-2013/Dec-2011/Feb-2010


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Position of weld symbol on the drawing:

The complete method of representation of the welds on the drawing comprises, in addition to the symbol

(3), the following (Fig. 11.3):


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.


Q.1 Draw the conventional representation of the

followingFillet weld, Spot weld

Feb-2010 7


followingFillet weld, Single V butt weld

Dec-2011 7


followingFillet weld, Square butt weld, Plug weld

Dec-2013 7


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Unit-01/Lecture-10/Additional Topics

RGPV Examination /June-2013/Dec-2011

Draw (i) the sectional view from the front, (ii) the view from above and (iii) the view from

the left and (iv) the view from the right of an anchor bracket shown in Fig. 4.15.


Draw (i) the sectional view from the front and (ii) the view from above of a bearing bracket

shown in Fig. 4.20.

RGPV Examination/Dec-2012

Draw (i) the view from the front and (ii) the view from above of the objects shown in Figs. 3.25


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Draw (i) the view from the front, (ii) the view from above and (iii) the view from the left of the

objects shown in Figs. 3.29


Q.1 Draw the sectional front view and top view of Anchor

bracket shown in fig 4.15

Dec.2011,

June-2013

10

Q.2 Draw the sectional view from the front and view from the

above of all bracket shown in fig 3.25

Dec.2012 10

Q.3 Draw the sectional front view and top view of Anchor

bracket shown in fig 4.20.

Feb.2010 10


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REFERENCCE

BOOK AUTHOR PRIORITY

Machine Drawing K.L.Narayana 1

Machine Drawing N.D.Bhatt 2


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Setting of page

1. Page no. at top in the center.

2. Theme font -Calibri

3. Main text font size-12

4. All headings in bold (12)

5. Top centre headings font size-14

6. Page A-4 size

7. Header and footer -08. margin -left (1.25), right (1)

9. Line spacing-1.00

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