AS019 Technical Drawing 2 Th Inst

7/25/2019 AS019 Technical Drawing 2 Th Inst

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SRI LANKA INSTITUTE of ADVANCED TECHNOLOGICAL

EDUCATION

Training Unit

Technical Drawing 2Theory

No: AS 019

Electrical and Electronic

EngineeringInstructor Manual


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Training Unit

Technical Drawing 2

Theoretical Part

No.: AS 019

Edition: 2008Al l Rights Reserved

Editor: MCE Industrietechnik Linz GmbH & CoEducation and Training Systems, DM-1Lunzerst rasse 64 P.O.Box 36, A 4031 Linz / Aus triaTel. (+ 43 / 732) 6987 3475Fax (+ 43 / 732) 6980 4271Website: www.mcelinz.com


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TECHNICAL DRAWING 2

LIST OF CONTENT

CONTENTS Page

LEARNING OBJECTIVES...................................................................................................3

1 REPRESENTATION OF COMPONENTS....................................................................4

1.1

Arrangement of the Views....................................................................................8

2 BASIC RULES OF DIMENSIONING.......................................................................... 11

2.1

Dimensioning of Square Components ...............................................................13

2.2 Rules for Dimensioning Square Components....................................................16

2.3

Dimensioning of Round Components ................................................................18

2.4 Rules for Dimensioning Round Components.....................................................19

2.5 Dimensioning Specific Details............................................................................22

3 SECTIONAL VIEWS...................................................................................................26

3.1 Full Section ........................................................................................................ 27

3.2 Half Section........................................................................................................29

3.3 Section in Two Planes and Part Section............................................................32

4 SYMBOLS FOR SURFACE FINISH...........................................................................36

4.1

Types of Symbol ................................................................................................36

4.2 Layout of Data....................................................................................................38

4.3 Standard Procedure...........................................................................................42


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TECHNICAL DRAWING 2

LEARNING OBJECTIVES

The trainee should ...

be able to indicate the three most important views required for the drawing of a work

piece .

be able to sketch the arrangement of the views and name them.

be able to name the three types of dimension.

explain when dots are used instead of arrows.

explain the arrangement and characteristics of a projection line, dimension line,

dimension arrow and dimension number.

explain the most important rules for dimensioning square and cylindrical work pieces.

determine when a work piece should be represented in full view and when it is

advisable to use half view.

be able to explain the arrangement, type and meaning of surface symbols.


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TECHNICAL DRAWING 2

1 REPRESENTATION OF COMPONENTS

There are various methods of representing a component. First there are the various three-

dimensional representations, which although very graphic, are extremely time consuming

and difficult to draw. Such three dimensional representations often serve as the model for

a particular problem and, therefore, will be briefly described. The simplest of these

representations is the oblique parallel projection.

SHOW FOIL No.: 1

All lines, which are drawn at 45, are shortened by half their true length.

Side ratio z : x : y = 1 : 1 : 0.5. In certain cases, this oblique parallel projection is also used

for sketches of components.


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Isometric projection and diametric projection:

- Side ratio x : y : z = 1 : 1 : 1

- Side ratio x : y : z = 1 : 1 : 0.5

SHOW FOIL No.: 1

These two representations are very time-consuming and difficult to draw.

The usual way of representing work pieces is by orthographic projection (DIN 6). With this

method the component must be drawn showing several views.


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The most important views are:

- Vertical projection or (f) front view = view from front

- Horizontal projection or (p) pIan view = view from above

- Lateral projection or (e) end view = view from left

In order to illustrate the development of the three views it is recommendable to imagine

the body to be projected suspended in one corner of a room.


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Three view planes at right angles to each other form the corner of the room.

For the drawing of a body all three-view planes must be shown in one view.

This is achieved by opening up and/or turning the horizontal and the side planes through

90 each.

By opening up the two view planes the two projection axes are obtained.


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1.1 Arrangement of the Views

The arrangement is standardized as shown below.

SHOW FOIL NO.: 2

Normally the three views shown in the square box are sufficient. It is possible to show

particularly complicated work pieces in up to six views. But very often only one or two

views are required for the illustration of a work piece. In this case only one view is

necessary. The distance across the flats is indicated with a reference line.


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If possible the components should be drawn in their manufactured position or when this is

not clearly known in the position they are used.

Sufficient distance should be left between the views to provide space for dimensions or

other information.

The following examples are to help the appreciation of three dimensions:


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2 BASIC RULES OF DIMENSIONING

Dimensioning is accomplished according three different methods. First the principal

dimensions are required (length, width and thickness), to enable material corresponding to

the basic shape of the component to be obtained from the stores.

These dimensions are termed:

- Overall dimensions:

These serve primarily for dimensioning the overall length, width, height or diameter.

- Progressive dimensions:

This method is used where dimensions are given from definite datum surfaces or

datum edges.

These datum surfaces (datum lines) must first be machined (filed, turned etc.). The

dimensions can then be built-up step by step.


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- Chain dimensions:

This method is used where a series of associated dimensions, such as, for example,

the width of slots or collars and their position, and the width of a number of spines.

NOTE:

Always enter the dimension for the slot width on one view.

If these three methods of dimensioning are combined, they provide a complete system of

dimensions.

SHOW FOIL NO.: 3

Dimensions of less than 10 mm are indicated with the arrows outside. Those greater than

10 mm with the arrows inside. If several dimension less than 10 mm occur in a row

(dimension chain), dots can be used instead of arrows.


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2.1 Dimensioning of Square Components

For square components, the system of dimensioning is determined by the marking out

procedure.

Marking out means transferring the dimensions necessary for manufacture from the

drawing to the component. The datum faces (datum edges) to be machined are placed on

the marking out table, and the dimensions are measured from that surface.

Distance of dimension line from edge of component pencil thickness (approx. 8 mm)


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Dimension lines are thin full lines; if possible they should be drawn outside the outline with

the aid projection lines. The distance from the edge of the component or to the next

dimension line is about 8 mm.

This distance of approx. 8 mm should be maintained where possible, because space will

be needed later for the surface symbols.

Dimension arrows should be in the form of a 15 isosceles triangle. The length of the

arrow is equal to the height of the dimension number. In many cases the space is too

restricted for arrows. In this case dots can be used instead of arrows.

Projection lines are thin full lines; they project about 2 mm beyond the dimension lines.

Projection lines are drawn at 90 from the edge of the component.

Conical components are exceptions to this rule - here projection lines are drawn at an

angle form the outline of the component.


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Dimension numbers should be written in standard lettering close above the dimension line

and the height of the lettering should not exceed 3.5 mm. If there is insufficient space

between the dimension arrows, the dimension number should be placed on right, or left,

outside and above the extended dimension line.

Examples of dimensioning:


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2.2 Rules for Dimensioning Square Components

All dimensions necessary for manufacture must be entered. All dimensions should be

directly measurable.

Right Wrong

Each dimension should only be entered once, on the view, which most clearly shows the

shape of the component.

Dimensions such as the width of slots, the depth and spacing of slots should be entered

on one view. All other dimensions may be advantageously distributed amongst the views.

Dimensions are given from datum edges or from centrelines.

Datum edges can be chosen on each component view.


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Where possible, dimensions should be given from the outline of the component with

projection lines.

SHOW FOIL No.: 4

Hidden edges (broken lines) may not be dimensioned.

Dimensions, which are to be measured, must be enclosed within the outline.

Measured dimensions are dimensions, which are very accurately measured and checked

during the final inspection.


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Dimensions, which are not to scale, must be underlined. If, for instance, a dimension on a

drawing is subsequently modified, the new dimension must be underlined. The dimension

20 is to be altered to 16 mm without modifying the drawing.

2.3 Dimensioning of Round Components

Dimensioning of round components is dictated by the sequence of manufacturing

operations. The unmachined component is first clamped in the lathe chuck.

The end-face is then faced off. This end-face serves as the "dimension datum face", from

which the diameters are turned in steps. (Enter the dimensions of the steps.) If there are

slots or shoulders etc., these must be dimensioned in a chain.


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When dimensioning circular components it is generally sufficient to place a diameter

symbol before the dimension number. This diameter symbol consists of a circle about 2/3

of the size of the lettering with a sloping line inclined at 75 passing through this circle.

This diameter symbol is only placed before the dimension number of the circular shape is

not visible.

2.4 Rules for Dimensioning Round Components

Always dimension from the datum surface (datum edge).

Datum surfaces can also be located at other points, depending on functional

considerations.


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Where several diameters are to be dimensioned, then for clarity, the dimension numbers

are placed on the left and right of the centreline.

When dimensioning outside turned work the dimensions are given from the outline of the

component. In this case the larger diameter should always be dimensioned above the

next smaller diameter.

Where possible, avoid cutting dimension lines with projection lines (however, this cannot

always be avoided).


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When dimensioning the diameters of turned components, not more than two dimensions

should be entered.

SHOW FOIL No.: 4

Recesses or thread undercuts should, if possible, be dimensioned with progressive

dimensions.

Never dimension the difference between diameters.

Always dimension the measurable diameter.

Centrelines should project approx. 3 mm beyond the end edges.

Related dimensions such as the diameter and width of recesses should always be

dimensioned on one view.


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2.5 Dimensioning Specific Details

Inclined faces:

A protractor is necessary for marking out the detail on the left.

Fehler! Es ist n icht mglich, durch die Bearbeitung von Feldfunktionen Objekte zu

erstellen.


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External and internal radii:

The radius R is placed before the dimension number if the centre of the circle is not

shown. However, the dimension line is positioned in such a way that when extended it

always passes through the centre of the circle.

If possible, centres of circles should be avoided outside the component.


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If the radius is very large, a flying dimension line can be used. The radius symbol R must

be placed before the dimension number.

If the centre point lies outside the outline of the component and is offset with respect to

the centreline, drawing a right-angled broken dimension line for the radius can specify the

dimension for the centre point.

Spherical surface:

When dimensioning a spherical surface the word (spherical must always be placed before

dimension numbers). When dimensioning with a "flying dimension" a diameter symbol

must be placed before the dimension number.


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Slots:

Slots are dimensioned according to the manufacturing process:

- By drilling:

Here the centres of the outer-drilled holes and the width of the slot are dimensioned.

The diameter of the hole should, if possible, be contained in the length of the slot (24 : 8 =

3x).

- By milling:

Here, the overall length of the slot can be dimensioned.

SHOW FOIL No.: 5


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3 SECTIONAL VIEWS

In general, only hollow components are sectioned. This renders the internal spaces

visible; they can be dimensioned in the sectional view and one view is thus often

eliminated.

Here two views are necessary, because

Hidden lines may not be dimensioned here only one view is sufficient

In a sectional view the component is regarded as being cut with a saw. The cut surfaces

are cross-hatched at 45 to the datum plane (it is left to the draughtsman to decide

whether this is to the left or the right). These hatching lines (symbolic representation of the

cutting marks) should be spaced approx. 2 to 3 mm apart and be drawn with thin full lines.

SHOW FOIL No.: 6


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3.1 Full Section

In a full section drawing the component is cut along the centreline. It is not necessary to

indicate the path of the cut.


erstellen.


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A full section is used when

- The view of the component is asymmetrical.

- The external view of the component has no special features requiring representation.

The component might also be symmetrical and it would then still be drawn in full

section (see diagram).


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3.2 Half Section

In a half section, one half of the component is shown in section and the other half as a full

view. The half shown in section and the half shown as an external view are separated by

a centreline (never by a thick full line).

SHOW FOIL No.: 6


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A half section is used when the view of the component is symmetrical and has projections,

collars and grooves etc. The sectional half is drawn on the left. However, in rotational

symmetrical components it is drawn above the centreline.


erstellen.

The dimensions of internal spaces are entered on the sectioned side. The projection lines

should be drawn through the hatching and must not be broken.


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If only one view is drawn of a flange with holes, half of the holes are drawn on the pitch

circle using a thin full line. They are rotated into the plane of the section (i.e. turned

through 90) only for sectional representation.


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3.3 Section in Two Planes and Part Section

Certain components frequently require the plane of the section to be displaced so that the

maximum number of holes can be shown. The exact line of the section must be indicated

in one view (usually the plan view).

A thick chain-dotted line at the beginning and at the end and also at the points indicates

the line of the section where the line of the section changes direction. Arrows must be

provided at the beginning and end of the line of the section.

These indicate the direction in which the section is viewed.


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In addition, large letters are placed at the beginning and end. Two successive letters (i.e.

A-B; C-D) for a section in two planes and two identical letters (i.e. A-A; B-B) for a straight

section. The section reference must be entered above the respective sectional view (i.e.

section A-B or section C-C etc.).

In the sectional drawing of this component the upper half has been rotated through 300

into the plane of the sections.

Ribs on a component should never be sectioned in a longitudinal direction because

otherwise they appear as solid parts.


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When ribs do not lie in the plane of the section they are regarded as being rotated in the

plane of the section, but no section is shown.

When ribs lie at right angles to the section they are shown in section for clarity.

A part section or a limited internal view of a component indicates that only a part of a

component is shown in section or exposed (for clarity or dimensioning).


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Part section Section A-A

Limited internal view

A thin free-hand line bound the section.


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4 SYMBOLS FOR SURFACE FINISH

The use of symbols to denote surface finish (DIN/ISO 1302) supersedes the earlier

conventional system of surface signs.

Advantage:

More comprehensive and more accurate data can be entered in a very restricted space.

Denoting surface quality by:

Surface signs symbols

4.1 Types of Symbol

The basic symbol consists of two straight lines of different lengths inclined at 60 to the

reference surface.


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There are three types of symbol:

- Basic symbol

on reference surface as group symbol

on the right above

the elevation

The thickness of the line is 1/10 of the height of the smaller leg. This basic symbol

acquires its meaning solely when used in combination with a descriptive word.

When such a descriptive word is used a horizontal line is added to the longer leg.

NOTE:

Descriptive words are always written horizontally.

The description always denotes the final condition.

Example:

Milled do not mill drilled do not drill etc.


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- Basic symbol with circle:

For chipless forming, i.e. cast, forged, rolled etc., a circle is added to the basic symbol.

- Basic symbol with transverse line:

For a machined surface, for example, shaped, milled, turned, drilled, reamed and fillet

etc., a transverse line is added to the basic symbol.

4.2 Layout of Data

The three types of symbol only specify whether machining is chip removing or chip less.

Further details are necessary for specifying the surface finish.


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a = roughness number (N1 - N12) or degree of roughness (Ra) in mm (1 / 1000 mm).

b = manufacturing process, treatment surface coating

c = test length in mm

d = direction of machining grooves

e = machining allowance in mm

f = additional roughness values (Rt, RZetc. )

a = roughness number (N1 - N12) or degree of roughness (Ra) in mm

SHOW FOIL No.: 8

Examples:


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b = Manufacturing process, treatment of surface coating

Information relating to a particular manufacturing process, treatment or surface coating

can be given on the extension line.

Examples:

Information relating to surface treatment (hardness data) is entered on a thick

chain-dotted line just above the surface to be treated.

C / f = Test length in mm/additional roughness data in

Examples:

The test length and the depth of roughness are only rarely specified in practice.

d = Machining groove direction (on the right next to the symbol)


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The following symbols indicate the general direction of the machining grooves.

= parallel to the plane of projection

= Perpendicular to the plane of projection

= Crossing (cross line)

M, C, R (for explanation see standard)

These symbols should only be entered when they are necessary for the functioning of the

component. The explanation of these symbols may be obtained, as required, from the

standard (DIN/ISO 1302).

Example:

e = Machining allowance

Where necessary, a value should be specified for the machining allowance (i.e. forsubsequent grinding); this is to be indicated on the left hand side of the symbol.

Example:


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4.3 Standard Procedure

The symbol and lettering must be arranged so that they can be read from the bottom and

from the right. The symbol must only be entered once for a given surface and at the point

where the particular surface is dimensioned.

If necessary, the symbol can be connected by a line with an arrow.

If the component is to have the same surface finish on all sides, then a group symbol must

be placed on the right above the front view, or following the part number.


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The words "on all sides" can be added.

If the same surface quality is to be provided on most of the surfaces of a work piece, this

must be specified as group symbols above the view. All additional symbols relating to the

work piece should be entered on the work piece, and must be specified in one of the

following ways beside the group symbol.

Variant 1

- Is preferable because it requires the least work (economical)


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Variant 2

- Gives greater detail

Variant 3

- Is very involved


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AS019Technical Drawing 2

Theoretical Test


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TECHNICAL DRAWING 2

TEST

1. Name the three most important views.

2. Sketch and define the arrangement of the three most important views.

3. Give an example for the case in which an arrow is replaced by a dot.

4. What is the extension of the projection line over the dimension line?

5. Draw and dimension a dimension arrow.

6. Explain when a diameter symbol is written before the dimension number.

7. Give the position of the half section for work pieces shown in a half section.

8. Draw the basic symbol for machined surfaces.

9. State the work pieces that are always shown in sectional views and give the reasons

for it.

10. Name the type of dimension that is used when dimensions are given from definite

datum surfaces or datum edges.


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9. Hollow work pieces are always shown in sectional views since the internal spaces

become visible and can be dimensioned. Sometimes, one view can therefore be

eliminated.

10. Progressive dimensions.


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AS019 Technical Drawing 2 Th Inst

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