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1、FORM TOLERANCESSECTION 3.1Form TolerancesToloerancesCharacteristicsSymbolFormStraightnessFlatnessRoundnessCylindricityProfile any lineProfile any surfaceForm tolerances of a feature control only form deviations of the feature.No datum is needed.There are 6 types of form tolerances.3.1.1 Straightness
2、The straightness is very important parameter for the lethe bed rail.3.1.1 StraightnessA straightness tolerance can be used to control the straightnessof surface elements or an axis.The tolerance specifies howclose to perfectly straight a feature must be made.3.1.1 Straightness(1)The tolerance zone i
3、s limitedby two parallel straight lines adistance t apart and in thespecified direction only.Any extracted line on the uppersurface,parallel to the plane ofprojection shall be containedbetween two parallel straightlines 0.05mm apart.0.05The tolerance zoneExample of indication3.1.1 Straightness(2)0.0
4、5The tolerance zoneExample of indicationThe tolerance zone is limited bytwo parallel planes a distance tapart.Any extracted(actual)generatingline on the cylindrical surfaceshall be contained between twoparallel planes 0.05mm apart.3.1.1 Straightness(3)The tolerance zoneExample of indicationThe toler
5、ance zone is limited bya cylinder of diameter t,if thetolerance value is preceded bythe symbol .The extracted median line of the cylinder to which the tolerance applies shall be contained within a cylindrical zone of diameter 0.05mm.0.05Flatness is a very important parameter for machine tool working
6、 surfaces.3.1.2 Flatness3.1.2 FlatnessFlatness tolerances are only used to specify a formcontrol for flat surfaces.3.1.2 Flatness0.05The tolerance zoneExample of indicationThe tolerance zone is limited bytwo parallel planes a distance tapart.The extracted(actual)surfaceshall be contained between two
7、parallel planes 0.05mm apart.3.1.3 Roundness Bearing bore for roundness and cylindrical precision of the request is very high.Roundness tolerances control the roundness of any feature that has a circular cross section,including cylinders and cones.Although a cone does not have a constant diameter,it
8、 does have a circular cross section.Circularity tolerances are often referred to as roundness tolerances.cylindercone3.1.3 Roundness 3.1.3 Roundness(1)0.05The tolerance zoneExample of indicationThe tolerance zone,in the considered cross-section,is limited by two concentric circles with a difference
9、in radii of t.Forthecylindricalsurface,theextracted circumferential line,inany cross-section of the cylindrical,shall be contained between twocoplanar concentric circles,with adifference in radii of 0.05mm.3.1.3 Roundness(2)The tolerance zoneExample of indicationThe tolerance zone,in the considered
10、cross-section,is limited by two concentric circles with a difference in radii of t.Any extracted circumferential line,resulting in the intersection of the(actual)revolute surface and asection cone shall be contained inaconicalzonelimitedbytwocircles 0.05 apart(this distance istaken on the generatrix
11、).0.053.1.4 CylindricityThe form of a cylindrical surface can be controlled by acylindricity tolerance.It can be applied to a shaft or hole.This tolerance type is,in effect,a combination of circularityand straightness tolerances.It also controls parallelism ofthe sides of the cylinder to prevent the
12、 part from beingtapered.cylinder3.1.4 CylindricityThe tolerance zoneExample of indicationThe tolerance zone is limited bytwo coaxial cylinderswith adifference in radii of t.The extracted(actual)cylindrical surface shall be contained between two coaxial cylinders with a difference in radii of 0.05mm.0.05