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Tolerance Analysis Pat Hammett
Geometric Dimensioning
and Tolerancing (GD&T)
Tolerance Analysis Methods
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Example: Joining Parts
n Suppose you want to join the following two parts.
n They need to be properly aligned and dimensionally
acceptable to insure a good assembly.
Height
Assembly
weld OK
Excess
Poor
Deviation
Align
weld weld
NOK NOK
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TQM - University of Michigan
Tolerance Analysis Pat Hammett
What is GD&T?
n Symbolized notation system municate
tolerances through the use of datums (references).
n GD&T is used whenever the location of a part is as
critical or more critical than its size. It insures that
two parts can mate or join properly.
n Thus, GD&municates 2 key issues:
n Datum Reference System (how part is held).
n Tolerances for Part Characteristics.
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Datums
n Datums define the reference system for a part
to measure or assemble it.
n reference systems may be absolute (XYZ) or relative (XY).
n Use pins ~ part holes or slots & clamps ~ part surfaces
A1 Clamp surface
to locator block
Hole:
(4-way locator) Slot: B2
(2-way locator)
A2
Clamp
ClampA3
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TQM - University of Michigan
Tolerance Analysis Pat Hammett
Symbols and Characteristics
Type of Tolerance Characteristic Symbol
Individual Feature Flatness
“ Diameter
Individual or
Profile
Related Features
Related Features Position
“ Parallelism
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GD&T Drawing Example
n Dimension may deviate up to 1mm any direction draw
circle with a radius = 1 (profile = 2 -> tol.+/- 1)
Dimension
(2mm total tolerance band relative to datums)
Geometric Tolerance Square Tolerance
Allows deviation of for T ***@45 = +/- 1
1mm in any direction tX = ; tY =
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TQM - University of Michigan
Tolerance Analysis Pat Hammett
Interchangeability & Tolerances
n Interchangeability -- given the asse