Tolerances of Form and Profile

1
Tolerances of Form and Profile

• Chapter 5
• Page 127

2
Objectives

• Identify the concepts and techniques of
  dimensioning and tolerancing to control the form
  and profile of geometric parts.
• Identify the different geometric characteristics
  that make up form and profile tolerances.

3
Tolerances of Form and Profile

• From tolerances control the following
• Straightness
• Flatness
• Circularity
• Cylindricity

4
Tolerances of Form and Profile

• Profile Tolerances Control the form and/or
  orientation of straight lines or surfaces, arcs,
  and irregular curves.
• Used when size tolerances provided in
  conventional dimensioning do not provide
  sufficient control for the function or
  interchangeability of a part or product.

5
Straightness Tolerance

• Straightness Tolerance Specifies a zone that
  the required surface element or axis must lie in.
• Straightness is a form tolerance.
• Condition where a surface or an axis must lie in
  a straight line

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Straightness Tolerance

• Geometric Characteristic Symbol for Straightness

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Straightness Tolerance

• Surface Straightness Tolerance Represented by
  connecting the feature control frame to the
  surface with a leader, or by connecting the
  feature control frame to an extension line.
• The feature may not exceed the MMC and perfect
  form must be maintained if the actual produced
  size is at MMC.

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Straightness Tolerance

• Examples

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Straightness Tolerance

• Axis Straightness Specified by placing the
  feature control frame below the diameter
  dimension, and a diameter symbol is placed in
  front of the geometric tolerance to specify a
  cylindrical tolerance zone.
• Perfect form is allowed to be violated at MMC.

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Straightness Tolerance

• If a material condition symbol is applied, the
  geometric tolerance is allowed to increase equal
  to the amount the actual size moves from the MMC
  or the LMC.

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Unit Straightness

• Unit Straightness Applied to a part in small
  increments to avoid having an abrupt surface
  variation within a relatively short length of the
  feature.
• The specified overall tolerance is usually bigger
  to keep the unit tolerance from getting out of
  control.

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Unit Straightness

• Unit straightness is used to divide a part up and
  have variation in a couple directions without
  major changes to the shape or form.
• When the unit tolerance per inch is specified,
  the feature control frame is doubled in height.
  The total tolerance is placed in the top box and
  the unit tolerance is placed in the bottom one.

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Unit Straightness

• Unit Straightness Callout

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Unit Straightness

• Examples

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Straightness of a Flat Surface

• Straightness of a flat surface is used to control
  single line elements on the surface in one or two
  directions.
• The position of the feature control frame will
  determine the direction the in which the
  tolerance will apply.

16
Flatness Tolerance

• Perfect Flatness The condition of a surface
  where all of the elements are in one plane.
• Flatness Tolerance Zone Establishes the
  distance between two parallel planes that a
  surface must lie in.
• Flatness is a form tolerance.

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Flatness Tolerance

• Flatness Symbol

.005
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Flatness Tolerance

• Flatness is specified by connecting the feature
  control frame to the feature with either an
  extension line or a leader line.
• All of the points of the surface must lie within
  the limits of the specified tolerance zone if
  flatness is called out.

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Flatness Tolerance

• The flatness tolerance zone must be less than the
  size tolerance when the surface is associated
  with a size tolerance.
• Flatness doesnt reference a datum and is always
  considered RFS.

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Flatness Tolerance

• Examples

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Specific Area Flatness

• Specific Area Flatness Calls out a specific
  area of a surface that has to flat.
• Good for large cast pieces that only have to have
  a small area finished rather than taking time to
  machine the whole thing.

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Specific Area Flatness

• Specific area flatness is outlined with phantom
  lines and then section lines are placed within
  the area.
• The area is located from the datum callouts on
  the print.
• Flatness area is usually called out as a square
  or rectangular surface.

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Specific Area Flatness

• Example

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Unit Flatness

• Unit Flatness Specified when it is desirable to
  control the flatness of a given area to avoid an
  abrupt surface variation within a small area.
• May be used alone or with a total tolerance call
  out.

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Unit Flatness

• Example

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Circularity Tolerance

• Circularity Any given cross section taken
  perpendicular to the axis of a cylinder or cone,
  or through the common center of a shape.
• Circularity Tolerance Formed by a radius zone
  created by two concentric circles that the actual
  surface must lie within.

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Circularity Tolerance

• Circularity Symbol

.005
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Circularity Tolerance

• Feature control frame is connected with a leader
  line to the view in which the feature appears as
  a circle.
• Circularity is always specified as RFS. No datum
  is to be used.

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Circularity Tolerance

• Example

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Free State Variation

• Free State Variation The distortion of a part
  after the removal of forces applied during
  manufacture.
• Nonrigid Parts Thin wall parts whose weight and
  flexibility are effected by internal stresses
  during machining.

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Free State Variation

• A free state symbol may be applied is a feature
  must be in tolerance while in a free state
  condition.

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Cylindricity Tolerance

• Cylindricity Identified by a radius tolerance
  zone that establishes two perfectly concentric
  cylinders that the actual surface must lie
  within.
• Feature control frame is connected to either the
  circular or longitudinal view.

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Cylindricity Tolerance

• Cylindricity Symbol

.005
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Cylindricity Tolerance

• Differences between circularity and cylindricity
• Circularity is a single cross sectional tolerance
  zone.
• Cylindricity is a tolerance that covers both the
  diameter and the length of the object.

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Cylindricity Tolerance

• Example

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Profile

• Profile Characterized as the outline of an
  object represented either by an external view or
  by a cross section through the object.
• True Profile The actual desired shape of the
  object.

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Profile

• Profile Tolerance Specifies a uniform boundary
  along the true profile that the elements of a
  surface must lie within.
• Used to control form, or the combinations of
  size, form, and orientation.

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Profile

• Profile tolerances are assumed to be bilateral
  unless otherwise specified.
• Profile tolerances may be specified between two
  given points or all around the object.
• Specified by connecting a feature control frame
  to the view or section that clearly shows the
  intended profile.

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Profile

• There are two profile geometric tolerances.
• 1. Profile of a line.
• 2. Profile of a surface.

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Profile of a Line

• Profile of a Line A two dimensional or cross
  sectional geometric tolerance that extends along
  the length of a feature.
• Profile tolerances are usually referenced to one
  or more datums.
• Used where its not necessary to control the
  profile of the entire feature.

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Profile of a Line

• Profile of a Line Symbol

.005
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Profile Between Two Points

• Shown by using the Between symbol under the
  feature control frame.
• Example

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Profile All Around

• Specified by placing the All Around symbol on
  the leader line.
• Example

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Unilateral Profile of a Line

• Unilateral Profile Where the entire tolerance
  zone is on one side of the true profile.
• A short phantom line is usually drawn parallel to
  the true profile to specify which side the
  tolerance is on.

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Profile of a Surface

• Profile of a Surface Used where it is desirable
  to control the entire surface as a single entity.
• Profile of a surface includes both the length and
  width of a feature or part.

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Profile of a Surface

• Profile of a Surface Symbol

.005
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Profile of Coplanar Surfaces

• Coplanar Surfaces Two or more surfaces on a
  part that are not on the same plane.
• Coplanar Profile Tolerance Used when it is
  desirable to treat two or more separate surfaces,
  that lie on the same plane, as one surface.

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Profile of Coplanar Surfaces

• Identified by connecting a leader line from the
  feature control frame to the phantom line and
  adding a note identifying the number of surfaces
  below the feature control frame.

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Profile of Conical Surfaces

• May be used to control the form, or form and
  orientation , of a conical surface.
• May be controlled independently or oriented to a
  datum axis.
• Requires that the actual surface lie between two
  coaxial boundaries equal in width to the
  specified geometric tolerance within the size
  limits.

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Profile of Conical Surfaces

• Example

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Composite Profile Tolerance

• Composite Profile Tolerance Provides for the
  location of a profiled feature and, at the same
  time, the control of form and orientation.

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Composite Profile Tolerance

• Example