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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