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STRAIGHTNESS OF LINES & SURFACES

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STRAIGHTNESS OF LINES & SURFACES

STRAIGHTNESS SYMBOL

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DEFINITION:Straightness is a condition where an element of a surfaceor an edge is in a straight line.

TYPICAL USE:

Typically used to control the form of cylindrical or conicalsurfaces. The straightness requirement applies to the

entire surface.

STRAIGHTNESS

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Straightness tolerance is specified on a drawing by means of a feature control symbol, which is directed by a leader to theline requiring control.

STRAIGHTNESS

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INTERPRETATION

The lines should be straightwithin 0.05 mm.

This means that the lineshould be contained within atolerance zone consisting of the area between two parallelstraight lines in the same

plane,separated by thespecified tolerance.

0.05

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STRAIGHTNESS

STRAIGHTNESS CHECKING WITH A STRAIGHT EDGE

Straightness can be measured by bringing a straight edge in contact withthe line, and determining the space between the straight edge and theline.

MEASURING

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If the feature tends towards convexity the height of the tolerance zone ismeasured where the least possible straightness error results.

MEASURING

Straightness includes all errors of form, such as concavity, convexity,

waviness, tool marks and other such imperfections.

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STRAIGHTNESS

STRAIGHTNES ERRORS IN A CYLINDRICAL SURFACE

ON CYLINDRICAL SURFACES

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STRAIGHTNESS

A straight tolerance when applied to the surface, controls surface elements only.It controls bending or a wavy condition of the surface, or a barrel shaped part.

Straightness not necessarily control the straightness of the centerline, nor conicity of the cylinder.

ON PROFILED SURFACES

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MEASUREMENT OF STRAIGHTNESS

MEASURING PRINCIPLE

The part is set up by suitable means, such as V-blocks on a surface plate, withthe surface to be evaluated closely parallel to the plate. Readings are thentaken at various points along the surface.

STRAIGHTNESS

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INTERPRETATION

Each line element of the surface shall be contained with in a tolerance zoneconsisting of the space between two parallel planes, separated by the width of thespecified tolerance, when the part is rolled along one of the planes.

STRAIGHTNESS

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ON CONICAL SURFACES

STRAIGHTNESS

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A straightness tolerance indicates in one direction only.

ON FLAT SURFACES

STRAIGHTNESS

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The straightness tolerances may all be shown on a single view byindicating the direction with short lines terminated by arrow heads.

FLAT SURFACES

STRAIGHTNESS

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ON REGULAR POLYGONS

Straightness tolerance applies to all of the longitudinal surfaces.

For all other shapes it applies only to those surfaces indicated unlessotherwise specified.

STRAIGHTNESS

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STRAIGHTNESS IN A SPECIFIED LENGTH

The expression 0.2/50 does not mean 0.2mm per 50mm of length.It means 0.2 mm in any 50mm long portion of the part.

STRAIGHTNESS

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