1

DRAFTING REVIEW

ELEMENTS OF A DRAWING

TYPES OF VIEWS

PART DRAWINGS

ASSEMBLY DRAWINGS

2

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.

3

PARTS OF A TYPICAL DETAIL DRAWING

sheet

titleBlock(TOC)

views

revisionblock

notes

4

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).

5

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”.

6

TITLE BLOCK

• 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

3rd angle projection symbol

7

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.

8

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.

9

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

10

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

11

ORTHOGRAPHIC VIEWS

12

Views using first angle projection;

used in Europe and Asia

Views using third angle projection;

used in North America

ORTHOGRAPHIC VIEWS

13

3rd Angle Projection

ORTHOGRAPHIC VIEWS

14

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

15

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

16

AUXILIARY VIEWS

17

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

18

section line

unique view label

cutting plane surfacecross-hatched

SECTION VIEWS

19

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

20

detailareawith label

detail view with labeland scale

DETAIL VIEWS

21

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.

22

orthographic views

isometric view

ISOMETRIC VIEW

23

CENTRE LINES

Used to indicate centres of full circles and axis of cylindrical features

24

DRAWING VIEWS IN SW

bracket.sldprt

flange.sldprt

shaft.sldprt

25

shaft.sldprt

DRAWING VIEWS IN SW

26

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

27

ASSEMBLY DRAWING AS ASSEMBLED

BOM

28

ASSEMBLY DRAWING SECTION VIEW

29

ASSEMBLY DRAWING EXPLODED VIEW

30

DIMENSIONING

31

OUTLINE

• General Rules

• Linear Dimensions

• Angular Dimensions

• Radial Dimensions

• Diameter Dimensions

• Holes

• Tolerances

32

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.

33

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.

34

LINEAR DIMENSIONS

extensionline

dimensionline visible gap

35

DIMENSION PLACEMENT

• Dimensions are placed outside the part. • Do not crowd dimensions and avoid crossing dimension lines with

extension lines.

aligned

space

space

36

ANGULAR DIMENSIONS

37

RADIAL DIMENSIONS

• Small radii are called fillets.• Preference is to use unlocated centres (easier to measure)

Unlocated Centre Located Centre

radiussymbol

centremark

leader line

38

RADIAL DIMENSIONS

• Never dimension to radii tangent points.

Tangent point

39

DIAMETER DIMENSIONS

centreline

diametersymbol

small diameters(arrows don’t fit inside)

large diameter

40

HOLE DIMENSIONS

• Multiple holes are common on parts so standardized symbols have been adopted.

Thru Hole Blind Drilled Hole

depthsymbol

note drillpoint

depth of fulldiameter

Thru Hole Blind Drilled Hole

41

COUNTERBORED HOLES

Thru Hole Blind Hole

counterboresymbol

counterborediameter & depth

Note: depths always measured from top surface

42

COUNTERSUNK HOLES

Blind Hole

countersinksymbol

countersinkdiameter & angle

again hole depthmeasured from topsurface

43

THREADS

• Standards used to describe threads.• Notes with leader are used to describe thread standard and

dimensions.

External Thread(Screw)

Internal Thread(Threaded Hole)

44

EXTERNAL THREADS ON DRAWINGS

MetricThread

AmericanThread

metric standard

major diameter

pitch

standard

major diameter

threads/inch(1/pitch)

Minor diametershown as hidden

chamfer

45

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.

must be atleast 4 threadsdeeper

Thru Hole Blind Hole

Major diametershown ashidden

Size of drilledhole given intables inMachinery’sHandbook

Usually show section view forblind threaded holes.

46

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.

47

COST OF TOLERANCES

48

TOLERANCE REPRESENTATION

• Several ways:– Limits:

– Bilateral:

– Unilateral:

– Single Limit:

– Reference Only:

(no tolerance)

25.024.8

24.9±0.1

250-0.2

25 MAX

(25)

49

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.

50

OVER DIMENSIONED

51

REPEATED FEATURES

Repeat symbol

52

WHAT IS WRONG?

lever.sldprt

53

WHAT IS WRONG?

54

WHAT IS WRONG?

55

WHAT IS WRONG?

56

WHAT IS WRONG?

57

WHAT IS WRONG?

58

WHAT IS WRONG?

flange.sldprt

59

WHAT IS WRONG?

60

WHAT IS WRONG?