DRAFTING REVIEW
ELEMENTS OF A DRAWING
TYPES OF VIEWS
PART DRAWINGS
ASSEMBLY DRAWINGS
1
INTRODUCTION
• Drawings are constructed to strict standards to ensure a consistent
interpretation.
– Often part of a contractual document
• Emphasis is on clarity and simplicity.
• Generally prefer to use symbols over notes since manufacturer may
not speak English.
2
PARTS OF A TYPICAL DETAIL DRAWING
sheet
revision
block
views
title
Block
(TOC)
notes
3
DRAWING SHEET SIZES
North America
International
A
8.5”x11”
A4
210mm x 297mm
B
11”x17”
A3
297mm x 420mm
C
17”x22”
A2
420mm x 594mm
D
22”x34”
A1
594mm x 841mm
E
34”x44”
A0
841mm x 1189mm
Choose sheet size such that drawing is filled but not crowded (based on number of
views and dimensions needed).
4
REVISION BLOCK
• Used to track changes to the drawing.
• Normally contains revision, description, date and approval.
• Description often refers to a separate document typically called a
“change order”.
5
TITLE BLOCK
3rd angle projection symbol
• Contains important information about the part or assembly.
• Specific format is company-dependent but information shown above
is commonly given.
• 3rd angle projection symbol important if drawing used internationally
6
DRAWING SCALE
• Title block indicates scale which is predominantly used for views on
drawing.
• If a view uses a different scale it must be indicated under that view.
• Scales are given as whole number ratios
– interpret as (drawing unit) : (physical unit)
– for scaling up: e.g. 2:1, 4:1, 10:1
– for scaling down: e.g. 1:2, 1:5, 1:20
– must have a 1 in the ratio. e.g. 2:3 not acceptable
• Scale is chosen so that the features can be clearly seen.
7
NOTES
• Gives useful information not covered by dimensions, symbols or in
the title block.
• Can also be used with arrows to indicate features of importance.
• Current practice is to limit the use of notes since they may be
misinterpreted.
8
DRAWING VIEWS
• Only use the number of views necessary to convey information
about the part (an isometric view is the exception)
• Often need only two or three views
• Edges which are visible in that view are shown as solid lines
• Edges which are not visible are called hidden lines
– Best not to show hidden lines
• you cannot dimension to hidden lines anyway
• they reduce clarity in drawings of complex parts
9
ORTHOGRAPHIC (PROJECTED) VIEWS
• Primary views on a drawing.
• Set of views at 90° to each other
• Created by placing part in a virtual box and look through each side.
• True size and shape
– angles are correct
– circles are round
– lengths are to scale
10
ORTHOGRAPHIC VIEWS
11
ORTHOGRAPHIC VIEWS
Views using first angle projection;
Views using third angle projection;
used in Europe and Asia
used in North America
12
ORTHOGRAPHIC VIEWS
3rd Angle Projection
13
ORTHOGRAPHIC STANDARD PRACTICE
• Choose front view as most descriptive
• Determine views to best represent object
• Use minimum number of views to completely describe object
• Views must be aligned
• Views should not be labeled
14
AUXILIARY VIEWS
• It is an extra view of an object
• It is used when the 6 principal views don’t describe an object (or
some of its features) clearly or completely - in particular inclined
features
• Should not be labeled
• It is used to show the true lengths of lines
• It is used to show the true size of planes
15
AUXILIARY VIEWS
16
SECTION VIEWS
• Useful to show interior features without using hidden lines
• Must show section line in another view which indicates the cutting
plane and the direction of view
• Does not need to be aligned with parent view but often is shown
aligned to enhance clarity
• Must have unique letter label
17
SECTION VIEWS
section line
unique view label
cutting plane surface
cross-hatched
18
DETAIL VIEWS
• Used as enlargement of another view to enhance clarity of small
features
• Must show detail area in parent view with label
• Is not aligned with parent view
• Must have unique letter label and scale must be indicated since it is
different from the parent view
19
DETAIL VIEWS
detail
area
with label
detail view with label
and scale
20
ISOMETRIC VIEW
• 3D view of part used to help visualization
• Common if 3D CAD system used to develop drawing
• Used only for a visual reference. Do not dimension this view.
• Common now for assembly drawings.
21
ISOMETRIC VIEW
orthographic views
isometric view
22
CENTRE LINES
Used to indicate centres of full circles and axis of cylindrical features
23
DRAWING VIEWS IN SW
flange.sldprt
bracket.sldprt
shaft.sldprt
24
DRAWING VIEWS IN SW
shaft.sldprt
25
ASSEMBLY DRAWINGS
• Assembly drawings show all the parts and how they go together.
• Dimensions are not usually required.
• A parts list or Bill of Material (BOM) specifies the item, quantity,
description, part number, etc. for each part.
• The item numbers from the parts list for each part are indicated
using numbered balloons in the view.
• Common styles used for assembly drawings:
– as assembled view
– section view
– exploded view - Preferred!
• Notes are used for assembly and machining instructions
26
ASSEMBLY DRAWING AS ASSEMBLED
BOM
27
ASSEMBLY DRAWING SECTION VIEW
28
ASSEMBLY DRAWING EXPLODED VIEW
29
DIMENSIONING
30
OUTLINE
• General Rules
• Linear Dimensions
• Angular Dimensions
• Radial Dimensions
• Diameter Dimensions
• Holes
• Tolerances
31
INTRODUCTION
• Dimensions give size, location and details of all features of the part.
• Manufacturing method is not specified but driven by dimensions,
material and tolerances.
• Dimensions are used per a standard to ensure consistent
interpretation and clarity
• Dimension standard often indicated on drawing in title block.
32
GENERAL RULES
•
Text height for dimensions and notes typically either .12” or 3 mm.
•
Text is always uppercase.
•
Units are usually either inches or millimetres.
•
If using inches:
– no zero precedes decimal (.250)
– dimensions expressed to same number of decimals as its tolerance
(.250±.002)
•
If using millimetres:
– zero precedes the decimal (0.5)
– no trailing zeros are required (2±0.5, 3.25±0.1)
•
Dimension text is always horizontal.
•
Do not dimension to hidden lines.
33
LINEAR DIMENSIONS
dimension
line
visible gap
extension
line
34
DIMENSION PLACEMENT
• Dimensions are placed outside the part.
• Do not crowd dimensions and avoid crossing dimension lines with
extension lines.
space
space
aligned
35
ANGULAR DIMENSIONS
36
RADIAL DIMENSIONS
• Small radii are called fillets.
• Preference is to use unlocated centres (easier to measure)
Unlocated Centre
Located Centre
radius
symbol
leader line
centre
mark
37
RADIAL DIMENSIONS
• Never dimension to radii tangent points.
Tangent point
38
DIAMETER DIMENSIONS
large diameter
diameter
symbol
centreline
small diameters
(arrows don’t fit inside)
39
HOLE DIMENSIONS
• Multiple holes are common on parts so standardized symbols have
been adopted.
Thru Hole
Blind Drilled Hole
depth
symbol
depth of full
diameter
note drill
point
40
COUNTERBORED HOLES
Thru Hole
Blind Hole
counterbore
diameter & depth
counterbore
symbol
Note: depths always
measured from top surface 41
COUNTERSUNK HOLES
Blind Hole
countersink
diameter & angle
countersink
symbol
again hole depth
measured from top
surface
42
THREADS
• Standards used to describe threads.
• Notes with leader are used to describe thread standard and
dimensions.
External Thread
(Screw)
Internal Thread
(Threaded Hole)
43
EXTERNAL THREADS ON DRAWINGS
metric standard
major diameter
pitch
Metric
Thread
Minor diameter
shown as hidden
chamfer
major diameter
standard
American
Thread
threads/inch
(1/pitch)
44
THREAD HOLES ON DRAWINGS
• Threaded holes are made by first drilling a plain hole and then
forming the threads using a tool called a tap.
Thru Hole
Major diameter
shown as
hidden
Blind Hole
Size of drilled
hole given in
tables in
Machinery’s
Handbook
Usually show
section view for
blind threaded
holes.
must be at
least 4 threads
45
deeper
TOLERANCES
• All real-world parts have variation in their features so every
dimension on the drawing must indicate the allowable variation.
– use of title block general tolerance note reduces clutter in
drawing
• The level of accuracy required is dictated by the fit & function of the
design.
• Tight tolerances = $$
– Designers try to use generous tolerances on non-critical
features.
46
COST OF TOLERANCES
47
TOLERANCE REPRESENTATION
• Several ways:
– Limits:
– Bilateral:
– Unilateral:
25.0
24.8
24.9±0.1
0
25
-0.2
– Single Limit:
25 MAX
– Reference Only:
(no tolerance)
(25)
48
DIMENSIONING TECHNIQUES
• Must give position and size of each feature but only once on the
drawing.
– do not dimension the same feature again in a different view
unless dimension for reference only
• Dimension based on the function of the feature.
• Dimension to reduce tolerance stack-up for critical features.
• Always dimension position of holes to their centre not their edge.
• Tolerance scheme in the solid model may not be suitable for the
drawing.
49
OVER DIMENSIONED
50
REPEATED FEATURES
Repeat symbol
51
WHAT IS WRONG?
lever.sldprt
52
WHAT IS WRONG?
53
WHAT IS WRONG?
54
WHAT IS WRONG?
55
WHAT IS WRONG?
56
WHAT IS WRONG?
57
WHAT IS WRONG?
flange.sldprt
58
WHAT IS WRONG?
59
WHAT IS WRONG?
60