Post on 14-Jan-2016
ToleranceTolerance
Geometric Tolerances and Dimensioning
Why Geometric Tolerancing and Why Geometric Tolerancing and
DimensioningDimensioning
To ensure interchangeability of mating To ensure interchangeability of mating parts during assemblyparts during assembly
To eliminate controversy and To eliminate controversy and guesswork when drawing is interpretedguesswork when drawing is interpreted
To ensure the drawing reflects the form To ensure the drawing reflects the form and function requirements of the and function requirements of the manufactured partsmanufactured parts
• Tolerances are used to control the variation that exist on all manufactured parts.
• Tolerance dimensions control the amount of variation on each part of an assembly.
• The more accuracy needed in the machined part, the higher the manufacturing cost
Limit Dimensions• Limits:
The lower and upper allowable sizes are
referred to as the limit dimensions
• Tolerance is :
a. Upper limits: Larger value
b. Lower limits: Smallest value
• Limit Dimensions
Tolerance Representation:Tolerance can be expressed in several ways:1. A general tolerance note in the title block
2. Direct limits, or as tolerance values applied directly to a dimension
3. Geometric tolerance
FIT TYPE• If one part is to be inserted
into or mated with another part, The type of fit can be determined by the following:
• The loosest fit is the difference
between the smallest feature A
and the largest feature B.
• The tightest fit is the difference between the largest feature A and the smallest feature B
Mating Parts• Mating parts are parts that fit together with a
reasonably high degree of accuracy.
Terminology of Tolerancing
• When the shaft and hole are assembled ,the extreme conditions are the tightest and the loosest fit
Methods of noting tolerance• TOLERANCE, UNILATERAL - A tolerance in which variation is
permitted in one direction from the specified dimension.
TOLERANCE, BILA TERAL - A tolerance in which - A tolerance in which variation is permitted in both directions from the variation is permitted in both directions from the specified dimensionspecified dimension
• Fit types
A. Allowance.
B. Clearance fit
C. Interference fit
D. Transition fit
E. Line fit
Clearance fit: Is the fit that gives clearance between
two assembled mating parts.Allowance fit: The allowance is the tightest fit between
two mating part.
Interference fit: Is the fit that leads to interference between two assembled parts.
.
• Transition fit: is a fit between two parts that can result in either interference or clearance.
Line fit: is a fit that can result in contact of surfaces between two parts or clearance.
Chain Dimensions
• Parts are dimensioned to locate surfaces or geometric features by chain of dimensions
• With each measurement based on preceding one, the tolerances accumulate
• Datum Plane The accumulation of tolerances can be reduced by measuring from a single plane called datum plan