The document provides guidance on creating assembly drawings and interpreting machine drawings. It discusses exploring product assemblies by investigating individual parts, functions, materials, and fastening techniques. Key points include representing assembled products through 3D CAD models after understanding individual parts. Assembly drawings should show all components in functional position and how they fit together using views and sections.

1. Assemblies
“Interpretation of machine and flat pack assembly drawings is a necessary skill for many
household and other common assemblies products, and these are seen as the primary
source of material for study”
“These skills are developed through the ability to interpret, model and represent multi
view projections from a number of single components.”
“Assemblies provide the ideal platform for 3D CAD Modelling.”
Design & Communication Graphics Syllabus, Page 33
In order to graphically represent an assembled product, it is first necessary to
investigate the product, and gain an appreciation for its individual parts,
design and function.

2. Exploration of Assemblies
• List the function(s) of the object
• Identify what contribution each part
makes to the overall function of the object
• Investigate how the necessary contribution
of each part impacts on its own design and
the overall design of the object
• Explore how the required function and hence
design of each part determines the choice of
material and surface finish
• Explore how the need for accessibility to various
individual parts of the object and design requirements
determines the fastening techniques
Function
Impact
Materials
Fastening

3. Product investigation
Applying this system to a common everyday object ……
…..Door bell switch
The primary function of the door bell switch is to
complete an electrical circuit to cause a bell to sound
A number of parts are required
in order for the door bell switch to
function successfully.
Function

4. Outer Casing – Contribution to function
Function
• To protect the other parts
from the elements
• To enclose the parts with
function and aesthetics in
mind
• The casing is not essential to the
operation of the door bell switch;
With the casing removed the button
can be used and the bulb stays
lighting

5. Outer Casing – Materials & fastening
The casing “clips” onto the mounting bracket
in a “push to fit” arrangement allowing access
to the workings inside.
A wedge shape protrusion keeps the casing in place.
The use of PTFE makes the casing durable
and pleasing to the eye
Materials
Fastening
Impact

6. Mounting Bracket – Contribution to function
The flange on the switch mounting lines
up with the collar on the mounting
bracket to keep it in position
The step at the base of the bracket
allows the light from the bulb to
illuminate the bell push;
The translucent acrylic disperses the
light effectively
Impact
Materials

7. • The mounting bracket has four main functions:-
- securing the outer casing
- locating the switch on the wall or door frame
- houses the switch mounting
- allows illumination of the door
bell switch
• Screws are used to fix the bracket
in place
- corrosion resistant coating
Function
Mounting Bracket – Contribution to function
Materials
Fastening

8. Sub Assembly – Switch Mounting
The switch mounting is a sub-assembly
within the main assembly.
It houses a number of parts which when
operated complete the circuit to sound
the door bell

9. Exploration of the button
The button;
• is made from PTFE
• is cylindrical in shape and
has filleted edges which make it
smooth to the touch
• houses a contact made from
copper;
which when brought in
contact with the circuited
contacts, sounds the bell
Material
Impact
Material
Function

10. Further parts of the Door Bell switch
• The circuited contacts are made from
copper – good conductor
• They are fastened in place
using self tapping screws
Material
• A spring is placed in between the
button and switch mounting.
• Repeat operation of the bell push.
• The spring is manufactured from
high tensile steel.
Function
Material

11. Further parts of the Door Bell switch
• A step at the base of the slot in
which the button contact moves
when operated prevents the
arrangement from coming apart
Impact
Fastening

12. Further parts of the Door Bell switch
• A bulb is inserted into a cylindrical
hole and is powered by fastening its
wires between the copper contacts
and base of the switch housing
• The door bell switch is powered by
connecting AC power to the two
contacts at the base of the switch
mounting. The self tapping screws are
loosened and the wires are looped
around the shafts of the screws.

13. Product investigation – Door Bell Switch
• By working through this process we gain an understanding
for the products individual parts, design and function.
• This understanding may be presented in digital images,
freehand sketches, CAD models, notes and detail drawings.

14. Graphical representation – Detail Drawing
• All necessary detailed information supplied to enable
manufacture without reference to another source
• Usually orthographic views
• Ample space allowed around each drawing for notes and
dimensions
• Material and surface finish may be specified

15. Assembly Drawings
• Shows all components assembled in functional position
• Indicates how components fit together
• Typically contains sectional views to add clarity
• Dimensioning of assembly not necessary, unless requested
- refer to detail drawings of components

16. Linetypes
Type A – Continuous thick – Visible outlines & edges
Type B – Continuous thin – Dimensions, projection and leader lines. Hatching
Type C – Continuous thin irregular
Type D – Continuous thin straight
with zigzags
Type E – Dashed thin – Hidden outlines & edges
Type F – Chain thin – Centre lines, lines of symmetry
Pitch lines and pitch circles
Type G – Chain thin, thick at ends
- Limits of partial or interrupted views
and changes of direction
- Cutting Planes

17. Scales
• Scale of drawings are always quoted
• All details generally drawn to the same scale.
• If not the scale should be clearly noted on
each detail drawing
Scale 2:3
Enlarged Scale
• Detail drawings of small components
are sometimes drawn larger than
actual size and larger details are
drawn to a reduced size
Scale 1:3

18. Projection Systems
• First or third angle projection are used in assembly drawings.
• The projection symbol is used to indicate which form of projection is used.
• Recommended proportions for projection symbol based on ‘D’
First Angle Projection Third Angle Projection

19. Terminology
Housing – a component into which a “male” mating part fits
Bush – a removable sleeve or simple bearing
It may be plain cylindrical or flanged.
The bush fits into the housing
and may be easily replaced
when worn.
Boss – a cylindrical projection on
the surface of a component
Plain Bush
Flanged Bush

20. Terminology
• Chamfer – bevelled or sloping edge
• Fillet – rounded portion or edge suppressing a sharp edge
• Flat – a surface machined parallel to the shaft axis
On a detail drawing, a flat surface is indicated with an X from
corner to corner.

21. Hub
Shaft
Key
Terminology
• Key – a small block inserted between
a shaft and hub to prevent the hub
from spinning freely on the axle
• Keyway – a slot or groove cut into a shaft
into which the key is placed.
• Note: A corresponding groove must
be cut in the hub.

22. Terminology
1. Through hole – A hole which passes all the way through a part
2. Blind hole – a hole that passes only partially through a part
3. Countersunk hole – provides a seat for a countersunk screw or rivet
4. Counter-bore – provides a housing for the heads of cap screws or bolts
5. Tapped hole – A hole with an internal thread to accept a bolt or screw.
Through hole
Blind Hole
Countersunk hole
Counterbore hole
Note: The countersunk or
counterbore holes will ensure
that the head of the screw is
under, or flush with, the surface

23. Terminology
• Rib/Web – a reinforcement positioned to support or stiffen
adjacent parts
• Spokes – a rod or bar, projecting radially from the hub of a wheel,
supporting the rim

24. Terminology - Fasteners
Round Head Screw – used
where an aesthetic finish is
required. Countersunk Screw – used
when the screw head must
be flush with the surface.
Socket Head Screw – Cylindrical head with a
hexagonal recessed drive.
Counterbored holes allow the head to
be flush with the surface.

25. Terminology - Fasteners
Grub-screw – used to prevent
relative motion between parts
eg. A pulley and shaft
Nut – Used, along with a
bolt, to fasten two or
more pieces together
Plain Washer - used to distribute
force from bolt or nut over a larger area
Spring Washer – causes friction lock to
hold nut in place and preven loosening
Plain Spring

26. Abbreviations
AC Across Corners
AF Across Flats
HEX HD Hexagon Head
ASSY Assembly
CRS Centres
CL Centre line
CHAM Chamfer
CH HD Cheese head
CSK Countersunk
CBORE Counterbore
CYL Cylindrical
DIA Diameter
Ø Diameter
R Radius
DRG Drawing
FIG Figure
LH Left hand
LG Long
MATL material
NO. number

27. Abbreviations
PATT No. Pattern number
PCD Pitch circle diameter
I/D Inside diameter
O/D Outside diameter
RH Right hand
RD HD Round head
SCR Screwed/screw
SPEC Specification
SFACE Spotface
SQ Square
STD Standard
UCUT Undercut
MC Machined
Mm Millimetre
NTS Not to scale
RPM Revolutions per minute
SWG Standard wire guage
REQD Required
MAX Maximum
MIN minimum

28. Conventional representations – Nuts & Bolts
• A bolt passes through two or more pieces and receives a nut or
other locking device to tighten and hold the parts together.
• Similar proportions exist between features in all nuts and bolts.
• Proportions are based on the diameter of the bolt
The centres C1,C2, and
C3 are found using the
60/30 setsquare.

29. Conventional representations – Threaded shafts
• A plain shaft is displayed as shown in a detail view.
• When screw threads are added they are conventionally
represented with type B lines.
Note the broken circle in the end elevation

30. Conventional representations – Threaded holes
• The lines representing the threads are Type B lines.
• Externally threaded parts are presented covering internally
threaded parts in sectional views.
Threaded shaft in a hole
Threaded Hole

31. Conventional representations - Springs
There are three categories of springs, based on function;
1. Compression
2. Tension
3. Torsion
• Coils may be drawn at either end or
• This simplified diagrammatic representation may be used.

32. Conventional representations – Spur Gears
• It is not necessary to show individual teeth on the drawing.
• The addendum and root circles are represented by solid circles.
• The pitch circle is shown as a chain line.
• The teeth are not sectioned as this would give a false sense of
solidity

33. Sectional Views
• Sections and sectional views
are used to show detail more
clearly, that would otherwise
be hidden.
• They are created using a
cutting plane to cut the
object.
• Visible outlines beyond the
cutting plane are included in
the sectional view.
• Note the representation of
the cutting plane in plan.

34. Types of Sectional Views
• Revolved section – Cross sections may be revolved in place.
• Offset section
Sectional views in two
or more parallel planes

35. Sectional Views
Local Section
• Used to avoid the need for a complete sectional view.
• Shows the detail at a specific location
Half section
• Symmetrical parts may be represented
half in outside view, half in symmetrical view.

36. Sectional Views – Hatching convention
Hatch lines are equally spaced and drawn, preferably, at 45°.
Separated sections of the same component should be hatched in the
same direction.
When different sectioned parts meet on an assembly drawing the
direction of the hatching should be reversed and staggered.
When hatching small areas the hatch may be represented with fill
colour.

37. Sectional Views – Hatching exemptions
Components exempt from hatching;
• Ribs
• Spokes
• Rivets
• Nuts
• Bolts
• Screws
• Washers
• Gaskets
• Keys
• Gear Teeth
• Shafts
• Pins

38. Dimensioning – Line types and arrow heads
• Dimension lines are narrow continuous lines
• A gap of 2mm to be allowed between the projection line and the
drawing.
• Projection line should extend the same distance beyond dimension line
• Arrowheads should be triangular, slender, filled in and touch the
projection line
• A spacing of approximately 12mm is recommended between rows
of dimensions
• Centrelines may be extended to act as projection lines

39. Dimensioning – Text placement
• Text is always read from the
bottom of the sheet or read
from the right
• Keep all dimensions outside the
drawing view where possible
• In general capital letters should
be used when notes are
required on a drawing
END ELEVATION
• The bottom of the dimension text is
always closest the dimension line.
• The text is centred on the
dimension with a 1mm gap
between it and the dimension line

40. Methods of Dimensioning
Parallel dimensioning
• Dimensioning more than one
feature from a common datum
Chain Dimensions
• Dimensioning from one feature to
the next.

41. Methods of Dimensioning - Circles
• A dimension displaying the diameter of
a circle is always preceded with Ø.
• Where a dimension may cross a projection
line the diameter may be dimensioned
using a leader line.
• The leader line, when extended, should pass
through the centre of the circle or arc.
• The dimensions of a diameter should be
place on a view that most clearly shows
the information.
• Projections of cylinders, or portion of, should always be
dimensioned as a diameter

42. Methods of Dimensioning - Holes
Typical methods of dimensioning holes are;
Methods of production are only specified where they are
necessary for function eg reamed.
Depth of a drilled hole refers to the depth of the
cylindrical portion only and not to the point of the drill

43. Item Referencing – Parts List
• Item references identify the items in an assembly.
• Item references are shown on an Items List
• Items list details the part number, part name and the number of
each item required.
• The item list may appear on the assembly drawing or separately.

44. Item Referencing – Balloon Referencing
• Numbers in balloons with leader lines, ending in dots, indicate
the components position on the drawing
• Numbers in balloons correspond to those in the item list
• Arrowheads may also be used touching the objects outline.
• Balloons should be placed orderly in horizontal or vertical rows
• Each item is referenced only once, even if it is duplicated within the
assembly.

45. Surface Finish
Surface finish is a measure of the roughness of the surface.
The roughness is determined by surface irregularities created during the
machining process used to create the part.
How much these irregularities deviate from a reference line determines the
roughness value.
Symbols are used for indicating the roughness value on detail drawings.
The basic symbol is a tick with the two legs inclined at 60° to the surface.
Surface viewed under a microscope
Reference Line

46. Surface Finish
• A bar is added to the basic symbol if the surface is to be machined.
• If removal of material is not permitted, a circle is added to the basic symbol
• The line thickness for the symbols is the same as that for dimensions.
• Symbols should be shown once on a surface;
Preferably on the same view as the size and location dimensions for the
surface.
Basic symbol Machining required No material removal

47. Surface Finish
• Surface roughness values are added to the symbols.
• When one value is specified it represents the maximum permissible
value of surface roughness
• Maximum and minimum values of surface roughness may also be given
The maximum is placed above the minimum
• When all of the surfaces are to be machined a general note may be
added along with a roughness value
3.2
3.2
2.6 3.2
ALL OVER

48. Welding Symbols
• Symbols are used to describe weld specification on detail drawings.
• Symbols detail information such as type of weld, size and side of joint on
which to weld.
• The basic part of a welding symbol is the reference line.
All welding symbols are tied to this line.
• An arrow connects the reference line to the joint to be welded
• When the weld type symbol is placed below the reference line the weld
is completed on the arrow side of the joint.
• When the weld type symbol is placed above the reference line it is
completed on the opposite side
• Symbol on both sides – weld both sides

49. Welding Symbols
• A flag on the junction of the reference line and the arrow line is present
if the weld is to be completed on site.
• If the flag is omitted; welding is to be completed in the workshop
• A circle is displayed on the junction if the joint is to be welded all round
eg. Pipe joints.
• The following symbols are used to distinguish between spot and seam
welds.
Spot Weld Seam Weld

50. Welding Symbols – Weld types
• A fillet weld is the most common weld type and is represented with the
triangular symbol.
• Other weld types are;
Square Butt Weld
Single Bevel Butt Weld
Double V Butt Weld
V Butt Weld

51. Assembly Drawings

52. Assembly Drawings

53. Assembly Drawings