BASIC ENGINEERING DRAWING - PowerPoint Presentation

Slide1

BASIC ENGINEERING DRAWING

Prepared By: Syed Basharat AliSlide2

Basic Engineering Drawing Contents

Ortho Graphic Projection

Lines

Sectioning

Terminology

Abbreviations

Conventional Representation Of Common Features

Pictorial Drawing

Dimensioning

Limits And Fits

Threads

Assembly

DrawingSlide3

Ortho Graphic Projection

In the engineering industry communication between the drawing office and the work shop is achieved mainly by means of engineering drawings. The principal method used to prepare these drawings is known as Ortho Graphic Projection.

Basically, Orthographic Projection is the representation of a three dimensional component on a flat surface (the drawing sheet) in two dimensional form. At least two orthographic views, therefore, are required to indicate fully the shape and size of a component. If the component is a complicated one then usually more then two views are shown to aid understanding.

In

this country two methods of a Orthographic Projection are used. One is known as First Angle Orthographic Projection (often referred to as English Projection), the other as Third Angle Orthographic Projection (American Projection). Both methods of representation are illustrated and explained in this sectionSlide4

First Angle Orthographic Projection

The

pictorial drawing opposite indicates the shape of the component with a single view.

An

orthographic drawing indicates the

Shape of a component by using a number of

views each looking at a different face of the

Component.At least two views are necessary to fullyrepresent the component. Usually , however, three views are shown in order to clarify internalAnd external detail. A Front View (F) A Plan View (P) A side View (L&R)Slide5

Front View

The

front view or front elevation represents what

is seen when

looking at the front of the component in

the direction

of arrow F

.Slide6

Plan View

A

plan view represent what is seen when looking at

the top

of the component in the direction of arrow P

.Slide7

Side View

The side view or side elevation represents what is seen when looking at the side of the component in the direction of either arrow R or arrow L. These arrows are at 90° to both arrow F and arrow P

.

View looking in

direction of arrow R.

Right- Hand

Side View (R)

View looking in

direction of arrow L.

Left- Hand

Side View (L)Slide8

In First Angle Ortho Graphic Projection The Front View is

Above

the Top view.

The Right-hand side view is on the

Left-hand

side of the front view.

The left hand side view is on the

Right-hand

side of the front

view.Slide9

Third Angle Orthographic Projection

When

representing a three dimensional component in Third Angle Orthographic Projection, the basic views

are exactly

the same as those shown when using

First Angle Orthographic Projection

. The

difference between First Angle and Third Angleis in the positioning of the views relative toeach other. In Third Angle OrthographicProjection the individual views are placed onthe drawing sheet in projection with each otheras shown:Slide10

Point For Third Angle

Orthographic Projection

The plan is always projected ABOVE the front view

.

The right-hand side view is shown on the

RIGHT-Hand

side of the front view.The left-hand side view is shown on the LEFT-Hand side of the front view.Slide11
Slide12

A Comparison Of First And Third Angle Ortho Graphic Projection

The plan is BLOW the front view.

The Right-hand side view is on the Left-hand side of the front view.

The left hand side view is on

the

Right-hand

side of the front

view.The plan is ABOVE the front view.The right-hand side view is on the Right-hand side of the front view.The left-hand side view is on the

Left-hand side of the front view.Slide13

Kind Of Lines

Kinds Of Lines

Line Group

(Intensity measured in mm)

Typical application

1,2

0,8

0,5

0,3

Solid

1,2

0,8

0,5

0,3

Visible

edge of parts; contours

0,4

0,3

0,2

0,1

Dimension

lines, extension lines, hatching lines, cross section lines, reference line, surface line, contour lines of adjacent parts.

Broken (dashed)

0,6

0,4

0,3

0,2

Invisible edges

Alternate long dashes with dots

1,2

0,8

0,5 0,3Lines indicating section planes.Center lines, Circular pitches, index circle, finished parts down machine allowance, ultimate lever position.Slide14

Common Lines Used In Engineering DrawingsSlide15

Sample DrawingSlide16

Sectioning

Drawings

of the outside of sample components are

often sufficient

to convey all the information necessary

to make

the component. More complicated

components, however mayrequire sectional views to clarify internals details.A sectional view is obtained when one imagines thecomponent to be cut through a chosen section plane often ona center line.If the vee-block is cut on section plane C-C as shownthe resulting sectional view projected from the planreplaces the usual front view

of the block.

Sectional Front View looking on cutting plane C-C

End ViewSlide17

Sectional views are drawn only when it is necessary to explain the construction of a complex object or assembly. Some of the examples used in the next few slides have been chosen to illustrate the rules of sectioning although in practice, as in the case of the

vee

-block drawn above a sectional view may not have been necessary.

The draftsman has to decide how a component or assembly should be sectioned in order to provide the fullest possible information. The recommendations of BS 308 enable him to do this in a way that is understood by all engineers.

Rules Of Sectioning

A sectioned object is shown by lines drawn preferably at 45°. Thin lines touch the outline. Size of sectioned part determines linespacing preferably not less than 4 mm.If two adjacent parts are sectioned , the section lines are drawnin opposite directions. Lines are staggered where the parts are incontact.Where more then two parts of an assembly are to be sectioned,the lines cannot all be opposite. Sectional lines are closer together

on the third area usually the smallestSlide18

The sectional view of a symmetrical object is obtained when the section plane

cuts through the obvious centre line. Hatching may be omitted if the meaning is

clear without it.

If an object is NOT symmetrical the section plane chosen should be clearly

stated.Slide19

Sectioning Exceptions

There are a number of a features and parts which are not normally sectioned even though they may lie in the section plane. A good way to accept these exceptions to be general rule is to imagine how complicated the drawing would look if they were sectioned. They are sectioned, however, when they lie across the section plane.Slide20

Staggered Section Planes

Section C-C Revolved

Section D-D Revolved

Section A-A Realigned

Each Part of the section plane is swung to the vertical before projecting to the sectional End view. By using the convention the draftsman avoids using too many auxiliary views. A staggered section plane should only be used when there is a resulting gain in clarity.Slide21

TERMINOLOGY

Communication between the drawing office and the work shop is mainly achieved via the engineering drawing orthographic or pictorial. In order to reduce drafting time a number standard parts are abbreviated.

Before this engineers “shorthand” can be correctly it is necessary to understand the terms used to describe features of engineering components. This terminology is common to both drawing office and workshop and is often used when discussing the various manufacturing and machining processes used in engineering.

Many different types of holes may be seen on engineering drawings. The more common ones, associated with drilling, reaming and tapping. The name and where appropriate the application of each is indicated.Slide22

A drilled hole or, if grater accuracy is required, a reamed hole.

A ‘blind’ tapped hole i.e. a threaded hole which passes only a part way through the plate.

A countersunk hole provides a mating seat for a countersunk head screw or rivet.

A counter bore provides a housing for the heads of cap screw, bolts, etc.

A spot face a much shallower circular recess. Provides a machined seat for nuts, bolt heads, washers, etc.Slide23

Abbreviations

Many terms and expressions in engineering need to be written on drawings so frequently as to justify the use of abbreviations which help to reduce drafting time and costs. A selection of the more commonly used ones are stated and clarified in the following table.

Abbreviation

Meaning

Sketch/Notes

A/C

Across corners

A/F

Across

flats

Hex HDHexagon head

ASSY

Assembly

CRS

Centers

CL

Center

line

CHAM

Chamfered

CH HD

Cheese head

CSK

Countersunk

C’ BORE

Counter boreSlide24

Abbreviation

Meaning

Sketch/Notes

CYL

Cylinder or Cylindrical

DIA

Diameter (In

a note)

ǿ

Diameter(preceding a dimension)

RRadius

(preceding a dimension, Capital only)

DRG.

Drawing

FIG.

Figure

LH

Left hand

LG

Long

MAT:

Material

NO.

Number

PATT NO.

Pattern number

PCD

Pitch circle diameter

I/D

Inside

diameter

O/D

Out side diameterSlide25

Abbreviation

Meaning

Sketch/Notes

RH

Right hand

RD HD

Round head

SCR

Screwed

SPEC

Specifications

S ‘ FACE

Spot face

SQ

Square

□

Square

(preceding dimension)

STD

Standard

U ‘ CUT

undercut

M/CD

Machined

mm

Millimeter

NTS

Not to be scale

RPM

Revolution per minute

SI symbol:

rev/min

SWG

Standard wire Gauge

TPI

Threads per InchSlide26

Conventional Representation of Common Features

Screw Threads

There are many components commonly used in engineering which are complicated to draw to full. In order to save drawing time, these parts are shown in a simplified, conventional form.

Subject

Convention

The screw thread is represented by two parallel lines. The distance between these lines is approximately equal to the depth of thread. The inside line is THIN and the circle is brokenSlide27

Springs

A spring is designated by stating the diameter of the wire, the coil diameter (inside or outside), the form of the spring ends, the total number of the coils and its free length.

in the case of compression spring, the pitch of the coil may be deduced from its free length and number of coil.Slide28

Shaft Details

it is frequently necessary to fix a component to one end of a shaft or spindle so that a torque may be transmitted.

Convention

Subject

Side View

Square on the end

of a long Shaft

Splined ShaftSlide29

Knurling

Knurling is a common method of providing a roughened to aid tightening or slackening of a screw by hand. This is formed by pressing special rollers against the surface of the component whist it revolves in lathe.

Diamond Knurl on a machine screw head

Straight Knurl on a circuit terminal

Subject ConventionSlide30

Long Components

There are occasions when bars, shafts, spindles or tubes may be too long to be drawn to a reasonable scale. In such cases the elevation may be interrupted .

Subject

Convention

Hollow Shaft “OR” Tube

Rectangular Bar

Circular Shaft “OR” SpindleSlide31

Multiple Holes

When a large number of holes of equal diameter are equally spaced around a diameter or a line, only one hole need be drawn in full with the reminder marked with a

short center line

.

That circle is called the pitch circle diameter or PCDSlide32

Gears

Before gears be drawn a great deal of background knowledge about their nomenclature and construction must be acquired.

Subject

Convention

Side view

of gear

wheel is

in section

Spur

Gear

WormAndWheelSlide33

A good example of a how a complex component maybe drawn relatively simply is the bevel gear. The assembly shown blow is of a pair of gear of equal size, the direction of motion being changed through an angle 90°. In the arrangement he gears are often referred to mitre wheel.

The gares ma be of differing sizes of course and the angle between the shaft may be other then 90°. In this letter case, the side view of the gear assembly would have to show one gear as then ellipse.Slide34

Pictorial Drawing

A

component may be represented graphically in various ways. An Orthographic Drawing, for example, requiring a minimum of two views to fully communicate the size and the shape of a component, is used in engineering mainly to convey manufacturing instruction from the designer to the craftsman. On the other hand a well executed Pictorial Drawing adequately representing all but the most complicated components using one view only, is used mainly as an aid

to visualization

of the shape of a component rather then

for communication

detailed instruction for manufacture.

A pictorial drawing, generally, is a quickly produced approximately scaled representation of a component a “picture” rather then an accurately scaled line drawing.There are many different types of pictorial representation. Two of the most commonly used ones are known as Isometric Drawingand Oblique Drawing.Slide35

Isometric

All receding lines are drawn at 30°Slide36

Oblique

An oblique pictorial drawing presents with the component with one of its faces as a true shape. This shape is drawn on the front face of the oblique box as shown below.

The longest face is usually drawn on the front of the oblique box with receding lines between ½ and ¾ full size.Slide37

Methods Of Construction

Of

Oblique

Drawing

There are many variations in angle, length of receding lines, and directions from which a component may be viewed in order to produce an oblique drawing as can be seen by examples on the previous slide. Different oblique drawings of the same component may each provide the details required.

The receding lines may be drawn at any angle to the horizontal but an

angle of 30, 45, 60 is proffered as lines can be drawn with set squares.

Receding lines may be any proportion of heir true length. A goodpictorial representation is obtained if lengths from ½ to ¾ actual length is used.Slide38

Dimensioning

A

number of the basic rules of dimensioning can be explained by reference to the above drawing of a thin plate.

The

sides marked A and B are known as DATUM faces. They are used as reference edges from which dimensions are drawn.

Datum's

may or may not be machined. Even if they are not machined it is good practice to choose reference edges in order to simplify the layout of dimensions.

Dimension Line: Thin full lines placed outside the component where possible and spaced well away from the out lines. The longer dimension lines are placed outside shorter ones.Projection Lines: Thin full lines which extend from the view to provide a boundary for the dimension line. Drawn at 90° to the out line.Arrowheads: Drawn with sharp strokes which must touch the extension lines. A Leader line is a thin full line which is drawn from a note, a dimension or, in this case, a “balloon” and terminates in an arrowhead or a dot. Relatively small gap.

Relatively short tail.Slide39

Crossing extensions lines usually a break to ensure clarity.

Dimension placed above the dimension line. This is preferred to the alternative method of placing the dimension in a gap in the line. Avoid using both methods on the same drawing if possible.

Dimension placed so that it may be read from bottom or right

hand side of the drawing sheet.Slide40

Arrangement Of Dimensions

Dimensions should be placed so that they may be read from either the bottom or right-hand side of a drawing, for example:

Various methods of dimensioning narrow spaces or width are shown above.Slide41

Dimensioning Circles

The way a circle is dimensioned the dimension always refers to the diameter and NOT the radius.

A circle is

never

dimensioned on a center line.

The conventional symbol for diameter is ∅.

The leader line must be drawn in line with the center of the circle.

In the example it is

preferable to dimensionthe side view even toughthe cylindrical shape isnot apparent. Dimension

in this view, however, mustalways be preceded bysymbol ∅.Slide42

Dimensioning Radii

A radius should be dimensioned by a dimension line which passes through, or is in line with, the center of the arc.

The dimension line should have one arrowhead which should be placed at the point of contact with the arc. The abbreviation R should always precede the dimension.Slide43

Dimensioning Angles

Angles are Expressed in:

Degrees e.g. 90°

Degrees and minutes e.g. 27 ° 30’

The placing of the angular dimension depends on the position of the angle in

relation to the bottom and/or the right-hand side of the drawing sheet and

the size of the angle.Slide44

Dimensioning Chamfers

45° chamfer should be specified by one of the methods below:Slide45

Location Dimensions

The features can be located from a machined surface or center line. Such s surface or line is known as DATUM.

Examples on pervious slides have been shown components and features may be dimensioned when size is the main consideration.

Spigot located from two reference edges ( R).

Both holes located from two reference edges ( R).

Both holes located from two reference edges ( R) then hole B related to hole A.Slide46

The simple bearing bracket casting on the left shows both size and location dimensions.

Reference surface are marked with machining symbol:-

This is placed so that it may be read from the right of the sheet.

It is preferable to place the symbol on the appropriate projection line rather than as show on the left.

No symbol is required where the machine is specified i.e. in the case of the drilled holes, the reamed holes and the spot-face.The location dimension are those show with letter Land size dimensions by a letter S. Some of the size dimensions are less accurate then other e.g. the thickness of the rib is fixed during the casting process whistle the 11 mm diameter holes is accurately reamed. The 20 mm diameter hole located by the dimension from the machined base to the center line of the hole.Slide47

Threads

A screw thread, often shortened to thread, is a helical structure used to convert between rotational and linear movement or force. A screw thread is a ridge wrapped around a cylinder or cone in the form of a helix, with the former being called a straight thread and the latter called a tapered thread. A screw thread is the essential feature of the screw as a simple machine and also as a fastener.Slide48

Pipe Threads G Series

These are parallel pipe threads having thread

angle of 55° and are used where pressure-tight

joints are not made on threads.

Taper Pipe Threads Whitworth Form

These threads have a taper of 1 in 16 and a

thread angle of 55° and are used where

pressure tight joints are made on threads.Slide49

American Pipe Threads

These threads have a taper of 1 in 16 and a

thread angle of 60°.  The types of threads

include NPT, NPTF & ANPT.

ACME Threads

Acme screw threads are mainly used for

the purpose of  producing traversing

motions on machines, tools etc. The multi-start threads are used to provide fast relative traversing motion.Slide50

Stub

ACME

The Stub Acme screw threads are generally

confined to those unusual applications like

transmission of power and motion where

a

coarse pitch thread of shallow depth is

required due to mechanical or metallurgical considerations.Trapezoidal ThreadTrapezoidal threads are used fortransmission of power and motion and arenearly similar to ACME threads, but are

made to metric dimensions and standards.The most commonly used class of threadsare 7e for external threads & 7H for internalthreads.Slide51

Buttress

Screw Thread

These are asymmetrical threads and are used

for transmission of power in one direction.

The most common thread profile is 7° / 45°.

Round Threads

These threads are also known as Knuckle

threads and are insensitive to dirt anddamage due to their round shape and areused in fastening screw threads in clutch ofrailway cars and for large valves and gates,for bottle caps etc.Slide52

Parts of ThreadSlide53

PITCH

The axial distance between threads. Pitch is equal to the lead in a single

start screw.

LEAD

The axial distance the nut advances in one revolution of the screw. The

lead is equal to the pitch times the number of starts.

LEAD = PITCH x STARTS

For example: 1/4" – 4 RH requires four turns for one inch of travel. A 1/4“– 4 RH has two starts and a 0.125" pitch. 0.125" pitch X two starts = 0.250“lead.SCREW STARTSThe number of independent threads on the screw shaft; example one, two

or four.Slide54
Slide55

Right Hand And Left Hand Threads

Right Hand Thread

A type of thread that is screwed in by rotating it clockwise.

Left Hand Thread

A type of thread that is screwed in by rotating it anti-clockwise.Slide56

Assembly Drawings

The

purpose of an assembly drawing is to provide visual information about the way in which parts of machine or structure fit together. There are several types of assembly drawings and the differences in presentation depend on the uses for which they are intended. They are:

Layout Assemblies

in which the designer places together all the various parts in order to established overall sizes, distances, etc. and as a result the feasibility of this design.

Outline Assemblies these gives general information about a machine or a group of components, for example, main sizes and centre distances which would show how the unit would be installed. This type of assembly is often used in catalogues giving details of the range of units offered for sale. General Assemblies or Arrangement Drawings shows clearly how components fit together and more important how the assembled unit functions'. Outside views, sectional and part sectional views may be used but dimensions are rarely needed. The various parts may be labeled by ballooning and parts list would complete the drawing. Sub-Assembly are drawings which show only one unit of a multi unit component. One more complicated or multiple part components it may first be necessary to arrange parts into sub assemblies which are then built up into the main assembly.Slide57

Sectioned Assemblies

a simple assembly may be drawn with out the need for sectional views and clearly understood. On more complex assembly drawings, however, too many hidden detail lines tend to confuse and a sectional view of the assembled parts conveys the information more clearly.