geometrical tolerences
TRANSCRIPT
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References and Suggestedreadings
Machine Drawing- N.D. Bhatt.Machine Drawing- Ajeet Singh.Machine Drawing- K.L. Narayana.Lecture Notes NPTEL.Machine Design Databook- McGraw HillPublications.
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Introduction
Dimensional Tolerances: Permissibleerrors in dimensions of a component.
Geometric Tolerances: Permissibleerrors in geometrical form of acomponent.
Surface Roughness: Surface qualityand texture.
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Types of Geometrical Tolerances
2. Position Tolerances:
Deviations in relative location of surfaces:
Radial run out Axial run out.Misalignment.Non Parallelism of axis.Incorrect location of intersecting axes.Non parallel surfaces.Non perpendicular surfaces.
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Need of Geometrical TolerancesTolerances of size are not always sufficient to
provide the required control of form.Fig. a, b and c shows some examples wheredimensions are within acceptable zone butgeometric form makes the componentsworthless.
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Geometrical tolerance - Maximum permissible overall variation of form or
position of a feature.Geometrical tolerances are used,
to specify the required accuracy incontrolling the form of a featureto ensure correct functional positioning of the feature
to ensure the interchangeability of componentsto facilitate the assembly of mating
components
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Tolerance zone: Imaginary area orvolume within which the controlled
feature of the manufactured componentmust be completely contained.Datum: Theoretically exact geometric
reference (such as axes, planes, straightlines, etc.) to which the tolerancefeatures are related.
Datum feature: Feature of a part, suchas an edge, surface, or a hole, whichforms the basis for a datum or is usedto establish its location.
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Representation
Datum Features
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Datum triangle :- The datum's are indicatedby a leader line, terminating in a filled or an
open triangleDatum letter :- To identify a datum forreference purposes, a capital letter isenclosed in a frame, connected to the datum
triangleDatum feature:- It is the feature to whichtolerance of orientation, position and run-outare related. The form of a datum featureshould be sufficiently accurate for its purposeand it may therefore be necessary in somecases to specify tolerances of form from the
datum features.
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Geometric Characteristic Symbols
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Representation of Straightness
This on Drawing
Means This !!! Each longitudinal element must liebetween two parallel lines (0.02mm apart) which are in same plane
with nominal axis of the part
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Representation of flatness
This on Drawing
Means This !!!
The surface mustlie within surfaceswhich are 0.25 mmapart
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Parallelism Example
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Representation of circularity
This on Drawing
Means This !!!
Each radial element in aplane perpendicular to theaxis must lie between twoconcentric circles havingradial difference of 0.25
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Representation of circularity
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Representation of circular run out
This on Drawing
Means This !!!
At any measuring position ,each circular element of thesurface must be withinspecified run out tolerance i.e.(0.02)
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Total Run out
This on DrawingMeans This !!!
Entire surface must liewithin surface runouttolerance zone
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Perpendicularity
This on Drawing
Means This !!!
Feature axis must liebetween two parallelplanes (0.2 apart) whichare perpendicular to datum
A
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AngularityThis on Drawing
Means This !!!
Surface must lie betweentwo parallel planes (0.4
apart) which are inclined at30 0 to datum plane A
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Material Conditions
Maximum MaterialCondition
Minimum MaterialCondition