1. BASIC ENGINEERING DRAWING
Prepared By: Syed Basharat Ali

2. Basic Engineering Drawing Contents
Ortho Graphic Projection
Lines
Sectioning
Terminology
Abbreviations
Conventional Representation Of Common Features
Pictorial Drawing
Dimensioning
Limits And Fits
Threads
Assembly Drawing

3. 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 section

4. 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 fully
represent the component. Usually , however,
three views are shown in order to clarify internal
And external detail.
A Front View (F)
A Plan View (P)
A side View (L&R)

5. 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.

6. Plan View
A plan view represent what is seen when looking at the top of the component in the direction of arrow P.

7. 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 L.
View looking in
direction of arrow R.
Right- Hand
Side View (R)
Left- Hand
Side View (L)

8. 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.

9. 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 Angle is in the positioning of the views relative to each other. In Third Angle Orthographic Projection the individual views are placed on the drawing sheet in projection with each other as shown:

10. 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.

12. 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.

13. Kind Of Lines Kinds Of Lines Line Group Typical application Solid
(Intensity measured in mm)
Typical application
1,2
0,8
0,5
0,3
Solid
Visible edge of parts; contours
0,4
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
Invisible edges
Alternate long dashes with dots
Lines indicating section planes.
Center lines, Circular pitches, index circle, finished parts down machine allowance, ultimate lever position.

14. Common Lines Used In Engineering Drawings

15. Sample Drawing

16. 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 may
require sectional views to clarify internals details.
A sectional view is obtained when one imagines the
component to be cut through a chosen section plane often on
a center line.
If the vee-block is cut on section plane C-C as shown
the resulting sectional view projected from the plan
replaces the usual front view of the block.
Sectional Front View looking on cutting plane C-C
End View

17. 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 line
spacing preferably not less than 4 mm.
If two adjacent parts are sectioned , the section lines are drawn
in opposite directions. Lines are staggered where the parts are in
contact.
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 smallest

18. 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.

19. 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.

20. Staggered Section Planes
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.
Section C-C Revolved
Section A-A Realigned
Section D-D Revolved

21. 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.

22. 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.

23. 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 HD
Hexagon head
ASSY
Assembly
CRS
Centers CL
Center line
CHAM
Chamfered
CH HD
Cheese head
CSK
Countersunk
C’ BORE
Counter bore

24. ǿ Abbreviation Meaning Sketch/Notes CYL Cylinder or Cylindrical DIA
Diameter (In a note) ǿ
Diameter
(preceding a dimension) R
Radius (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 diameter

25. Square (preceding dimension)
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 Inch

26. 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 broken

27. 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.

28. 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.
Subject
Convention
Square on the end
of a long Shaft
Side View
Splined Shaft

29. 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.
Subject Convention
Diamond Knurl on a machine screw head
Straight Knurl on a circuit terminal

30. 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
Rectangular Bar
Circular Shaft “OR” Spindle
Hollow Shaft “OR” Tube

31. 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 PCD

32. 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
Worm
And
Wheel

33. 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.

34. 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 Drawing
and Oblique Drawing.

35. Isometric
All receding lines are drawn at 30°

36. 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.

37. 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 good
pictorial representation is obtained if lengths from ½ to ¾ actual length is used.

38. 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.

39. 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.

40. 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.

41. 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 dimension
the side view even tough
the cylindrical shape is
not apparent. Dimension
in this view, however, must
always be preceded by
symbol ∅.

42. 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.

43. 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.

44. Dimensioning Chamfers
45° chamfer should be specified by one of the methods below:

45. 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.

46. 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 L
and 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.

47. 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.

48. Pipe Threads G Series Taper Pipe Threads Whitworth Form
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.

49. American Pipe Threads ACME 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.

50. Stub ACME Trapezoidal Thread 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 Thread
Trapezoidal threads are used for
transmission of power and motion and are
nearly similar to ACME threads, but are
made to metric dimensions and standards.
The most commonly used class of threads
are 7e for external threads & 7H for internal
threads.

51. Buttress Screw Thread Round Threads
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 and
damage due to their round shape and are
used in fastening screw threads in clutch of
railway cars and for large valves and gates,
for bottle caps etc.

52. Parts of Thread

53. PITCH LEAD SCREW STARTS
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 " pitch X two starts = 0.250“
lead.
SCREW STARTS
The number of independent threads on the screw shaft; example one, two
or four.

55. 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.

56. 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.

57. 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.