Tolerance analysis :
Study of individual tolerances
Process of determining the cumulative variation
possible between two or more features.
Tolerance stack up analysis is one part of tolerance
Analyzes and predicts the variation between the
Determines the maximum possible variation
between two components in an assembly.
Merits of Tolerance Stack Up Analysis
Optimize the tolerances of parts and assemblies in a
Balance accuracy , precision and cost with
Determine the part tolerance required to satisfy a
final assembly condition
Determine allowable part tolerance if assembly
tolerance is known
Determine the effect changing a tolerance will have
on assembly component
Steps in Tolerance Stack Up Analysis
The Distance to be studied is identified and labeled
The positive and negative directions are identified
A tolerance stack up sketch is created
The dimensions in positive direction and negative
directions are added individually
The nominal distance is found out by subtracting
negative direction total from the positive direction total
The total possible variation is obtained by adding all
The maximum and minimum variations are obtained
from the nominal distance and total variation values.
For an inseparable
tolerance stack up
analysis find the
between the part 5 and
6 in assembly.
Dimensional Chain Analysis
Dimensional Chain is a consecutive series of interrelated
dimensions that contribute to the tolerance of a dimension and form
a closed loop.
Two Basic tasks in tolerance design process :
Dimensional Chain analysis
Dimensional Chain synthesis
In Dimensional analysis component tolerance are specified and
resulting assembly variation is calculated.
Dimensional Synthesis involves allocation of specified assembly
tolerance between component dimension of the assembly.
Equivalent tolerance method
All independent dimensions have same tolerance
Used when all independent dimensions in the analysed
dimensional chain have same nominal value.
Deterministic approach formula is
Stochastic approach formula is
Equivalent Standard tolerance grade
All independent dimensions are assigned tolerance
values from the same tolerance grade.
Value of dimension tolerance is :
Txi = tolerance of ith independent dimension
Xi = nominal value of ith independent dimension
K =unknown tolerance grade factor
Two holes are drilled in a plate. What are the
required tolerances of dimensions A,B,C,D if the
tolerance of the dependent dimension Z is required as
not greater than 140 µm and the nominal values of
the independent dimensions are A=124mm,