Transcript Geometric Dimensioning and Tolerancing

Geometric Dimensioning and
Tolerancing
Unit 1 – Introduction, Symbols, and Terms
History and Background
Eli Whitney, is the inventor of the
cotton gin and a pioneer in the
use of mass production methods.
Around 1798, he won a contract
to supply muskets to the United
States government. The firearms
manufacture were based on the
concept of interchangeable parts.
He made a presentation to
congress by building 10 guns and
assembling and disassembling
them claiming the same exact
parts and mechanisms.
Eli Whitney 1765 - 1825
EML 2023
Computer Aided Design
Limit Tolerancing
EML 2023
Computer Aided Design
Limit Tolerancing
EML 2023
Computer Aided Design
Limit Tolerancing
• Is the .620-.630 hole horizontal position
measured from a true vertical plane or from the
as built face?
• A .005” tolerance on the horizontal and vertical
position of the hole means that the position
could be off by as much as .007”.
max allowed error
for hole center
.007
perfect location
for hole center
+.005
+.005
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Computer Aided Design
Limit Tolerancing
• Limit tolerances don’t have an origin or any orientation or
location relative to datums.
• The datums are usually implied.
• The drawings are subject to different interpretations.
• Plus/minus tolerancing works well for individual features
of size (ex. diameter of a shaft), but does not control the
relationship between individual features very well.
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Computer Aided Design
Geometric Tolerancing Workbook
Everyone should have a
workbook to follow along.
It contains necessary
reference information along
with class exercises.
Page numbers in yellow on
the slides match pages in
the workbook.
EML 2023
Computer Aided Design
History of Dimensioning and
Tolerancing Standards in the USA
Mil Std 8 1950’s
Mil Std 8A
Mil Std 8B
Mil Std 8C-1963
ASA-Y14.5-1957
USASI Y14.5-1966
ANSI Y14.5-1973
ANSI Y14.5M-1982
ASME Y14.5M-1994
ASME Y14.5-2009
1.3
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Common Symbols
Lightning bolts show new symbols
1.7
Geometric
Characteristic
Symbols
1.10
Common Tolerance Zone Shapes
1.11
Geometric Tolerance
Categories
“Happy Features”
1.12
Features of Size
and
Features without Size
1.9
Tolerances
• All dimensions require a tolerance.
• A tolerance should be as large as possible
without interfering with the function of the part to
minimize production costs.
• Consider how your part will be checked to see if
it meets the tolerances.
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Computer Aided Design
Tolerance Notes
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Geometric Dimensioning and
Tolerancing (GDT)
1. establish a reference coordinate system by
defining datums
2. provide basic dimensions (perfect dimensions)
relative to the datums
3. specify allowable tolerances
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Computer Aided Design
Common Symbols
units are mm
applied to a Drawing
25
10
18
±1°
1.8
A
C
B
Specify flatness.
Document tolerances for the center hole.
Document tolerances for the outer holes.
Document tolerances for the square hole.
Document tolerances for the three slots.
Dimension the thickness.
Indexer Assembly
1.17
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Computer Aided Design
Indexer Plate
1.17
EML 2023
Computer Aided Design
Indexer Assembly
ASME Y14.41 - 2003, Digital Product
Definition Data Practices
1.19
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Computer Aided Design
Workshop Exercise 1.1
12
1.23