MKSSS’s
Cummins College of Engineering for Women, Pune
Department of Mechanical Engineering
Second Year of Engineering
Subject Name: Machine Drawing
Subject Code : ME 2104
Subject Teacher : Prof. Vishwanath Mali
Contact : vishwanath.mali@cumminscollege.in
A
Presentation
On
UNIT V
Geometric Dimensioning and Tolerance
by
Prof. V. A. Mali
Department of Mechanical Engineering
Syllabus
• Need of Geometric Tolerance
• Geometric characteristics of symbols
• Characteristics tolerances for related features such as straightness,
Flatness, Circularity, Cylindricity, parallelism, perpendicularity,
angularity, concentricity, its symbols and interpretations.
Introduction
• Manufactured items differ in size and dimensions from the original
CAD model due to variations in the manufacturing processes.
• To optimally control and communicate these variations, engineers
and manufacturers use a symbolic language called Geometric
Dimensioning and Tolerancing (GD&T).
• It is a standard published by the American Society of Mechanical
Engineers (ASME) and is considered as authorized language for GD&T.
• Geometric Dimensioning and Tolerancing (GD&T) is a language of
symbols and standards designed and used by engineers and
manufacturers to describe a product and facilitate communication
between entities working together to produce something.
• The standard used was ASME Y14.5 -1994 and now, AMSE Y14.5-2009
is used.
• Increased use of worldwide standards, such as ISO 9000, which
require universally understood and accepted methods of
documentation.
• Precision and accuracy
• Reduce rework cost
• Reduce Defects
• Increase Understanding
Geometric characteristics of symbols
• It depends on the types of geometrical tolerances
1. Form tolerance
2. Orientation tolerance
3. Location tolerance
4. Profile tolerance
5. Runout tolerance
1. Form tolerance
• Control the shape of features and used as refinement of size.
• Form tolerance are applicable to single features, no relation between
features.
• Form tolerance controls straightness, flatness, circularity and
cylindricity.
2. Orientation tolerance
• It controls the tilt of features and used as refinement to location.
• An orientation tolerance controls parallel, perpendicular and all other
angular relationships.
3. Location tolerance
• It controls the location.
• It includes position, concentricity and symmetry.
4. Profile tolerance
• A profile tolerance may be applied to an entire part, multiple
features, individual surfaces or to individual profile.
• It includes line profile and surface profile
5. Runout tolerance
• Runout is a tolerance used to control the functional relationship of
one or more features to a datum axis.
• It includes circular runout, total runout.
General terms
• Geometric tolerance: It is the maximum permissible variation of
form, profile, orientation, location and run out specified on machine
drawing.
• Feature: Feature is the specified portion of a component such as
hole, slot surface or profile.
• Frame: Frame is a box having partitions. Each partition contains
information about the following..
• Datum: Datum is a theoretical point, line or plane from which
dimensions are measured and geometric tolerances are referenced.
• Datum triangle: Datum is shown by triangle (open or filled) on the
datum feature.
• Datum letter: It is an upper case letter enclosed in a box to indicate
an arbitrary name of datum.
• Multi-datums: Normally one datum is required for orientation but
position tolerance may require two or more datum.
• Material Condition (MMC and LMC)
• Maximum material condition (MMC): It is condition in which feature
contains maximum material.
• Least material condition (LMC): It is condition in which feature
contains least material.
Characteristics tolerances for related features
• Straightness
• Flatness
• Circularity
• Cylindricity
• Parallelism
• Perpendicularity
• Angularity
• Concentricity
• Circular runout
• Total runout
Straightness
• It is the perpendicular distance between two parallel lines touching to
crests (the highest point) and valleys (the lowest point) of the line.
Flatness
• It is the distance between two imaginary planes enclosing the actual
surface at lowermost and uppermost positions.
Circularity
• Circularity is also called roundness.
• Theoretically, any point on cylindrical surface from the central axis
should be at the same distance.
• Due to problems in machine tools, it may not be round as shown in
figure.
• Tolerance value of circularity is the difference between maximum and
minimum radii of a cylinder at any section.
Cylindricity
• It is the difference in value of radii between two imaginary cylinders,
at outermost and innermost surfaces.
• Figure shows the variation in the surface of a cylinder along its axis.
• The diameter at every cross section is different and lies in circular
zone.
Parallelism
• A surface which is required parallel to datum may not be exactly
parallel.
• Tolerance on parallelism is the zone between two parallel surfaces
enveloping the feature in relation to datum surface.
• Gap between two enveloping plane is called geometric tolerance on
parallelism.
Perpendicularity
• Perpendicularity tolerance is the zone between two perpendicular
planes to the datum within which the controlled features lies.
• It is also called tolerance on squareness.
Angularity
• Tolerance on angularity is the zone between two parallel planes
inclined to the datum plane at the specified angle in which controlled
features lies.
• Note that tolerance on angularity is not defined in terms of angles.
Concentricity
• Theoretically, a perfect concentricity means that the axes of two
coaxial cylinders are in a line and coincide.
• Tolerance on concentricity is the diameter of a circular zone within
which the axes of two cylinder features may offset from each other.
Symmetry
• Theoretically symmetry means the position of a feature is symmetric
in relation to datum.
• In the figure inclined surfaces should be symmetrical about the
central axis.
Position
• It is the location of a feature relative to one or more datums.
• The actual centre of the hole may lie within a tolerance zone
indicated by a small circle of diameter 0.1 mm.
Profile of a line
• Tolerance zone for a profile of a line controls the contour of a curved
profile.
• Figure shows the variation in actual top surface.
• The variation lies between the two curves which envelop the actual
curve.
Profile of a surface
• Tolerance zone for a profile of a surface is the space between two
surfaces of a same profile which envelop the highest point and lowest
point of surface keeping the same profile.
Circular Runout
• Circular run out is the deviation from an ideal shape when part is
rotated by 360°.
• It could be radial or axial or both.
Total Runout
• Total run out is not a circular run out at one particular position but
found when dial indicator is moved axially over the entire surface
parallel to the axis of datum while the part is being turned.
• The difference in minimum and maximum dial indicator reading from
beginning to the end while rotating the surface is the total run out .
