1 DRAFTING REVIEW ELEMENTS OF A DRAWING TYPES OF VIEWS PART DRAWINGS ASSEMBLY DRAWINGS
Jan 19, 2016
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DRAFTING REVIEW
ELEMENTS OF A DRAWING
TYPES OF VIEWS
PART DRAWINGS
ASSEMBLY DRAWINGS
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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.
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PARTS OF A TYPICAL DETAIL DRAWING
sheet
titleBlock(TOC)
views
revisionblock
notes
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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).
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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”.
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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
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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.
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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.
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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
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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
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ORTHOGRAPHIC VIEWS
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Views using first angle projection;
used in Europe and Asia
Views using third angle projection;
used in North America
ORTHOGRAPHIC VIEWS
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3rd Angle Projection
ORTHOGRAPHIC VIEWS
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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
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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
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AUXILIARY VIEWS
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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
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section line
unique view label
cutting plane surfacecross-hatched
SECTION VIEWS
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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
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detailareawith label
detail view with labeland scale
DETAIL VIEWS
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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.
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orthographic views
isometric view
ISOMETRIC VIEW
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CENTRE LINES
Used to indicate centres of full circles and axis of cylindrical features
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DRAWING VIEWS IN SW
bracket.sldprt
flange.sldprt
shaft.sldprt
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shaft.sldprt
DRAWING VIEWS IN SW
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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
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ASSEMBLY DRAWING AS ASSEMBLED
BOM
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ASSEMBLY DRAWING SECTION VIEW
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ASSEMBLY DRAWING EXPLODED VIEW
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DIMENSIONING
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OUTLINE
• General Rules
• Linear Dimensions
• Angular Dimensions
• Radial Dimensions
• Diameter Dimensions
• Holes
• Tolerances
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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.
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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.
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LINEAR DIMENSIONS
extensionline
dimensionline visible gap
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DIMENSION PLACEMENT
• Dimensions are placed outside the part. • Do not crowd dimensions and avoid crossing dimension lines with
extension lines.
aligned
space
space
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ANGULAR DIMENSIONS
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RADIAL DIMENSIONS
• Small radii are called fillets.• Preference is to use unlocated centres (easier to measure)
Unlocated Centre Located Centre
radiussymbol
centremark
leader line
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RADIAL DIMENSIONS
• Never dimension to radii tangent points.
Tangent point
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DIAMETER DIMENSIONS
centreline
diametersymbol
small diameters(arrows don’t fit inside)
large diameter
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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
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COUNTERBORED HOLES
Thru Hole Blind Hole
counterboresymbol
counterborediameter & depth
Note: depths always measured from top surface
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COUNTERSUNK HOLES
Blind Hole
countersinksymbol
countersinkdiameter & angle
again hole depthmeasured from topsurface
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THREADS
• Standards used to describe threads.• Notes with leader are used to describe thread standard and
dimensions.
External Thread(Screw)
Internal Thread(Threaded Hole)
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EXTERNAL THREADS ON DRAWINGS
MetricThread
AmericanThread
metric standard
major diameter
pitch
standard
major diameter
threads/inch(1/pitch)
Minor diametershown as hidden
chamfer
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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.
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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.
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COST OF TOLERANCES
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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)
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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.
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OVER DIMENSIONED
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REPEATED FEATURES
Repeat symbol
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WHAT IS WRONG?
lever.sldprt
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WHAT IS WRONG?
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WHAT IS WRONG?
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WHAT IS WRONG?
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WHAT IS WRONG?
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WHAT IS WRONG?
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WHAT IS WRONG?
flange.sldprt
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WHAT IS WRONG?
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WHAT IS WRONG?