Scribd
Upload
249 views6 pages

Geometric Dimensioning & Tolerances: G D & T Symbols

Geometric Dimensioning and Tolerancing (GD&T) uses standard symbols to indicate tolerances based on a feature's geometry. It describes tolerance zones around a feature's theoretically exact location rather than a square tolerance zone. GD&T uses feature control frames and datums as reference surfaces to define tolerances for features. Common GD&T tolerances include circular runout, total runout, concentricity, and angular tolerances.

Uploaded by

parthiban
Copyright
© Attribution Non-Commercial (BY-NC)
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
249 views6 pages

Geometric Dimensioning & Tolerances: G D & T Symbols

Geometric Dimensioning and Tolerancing (GD&T) uses standard symbols to indicate tolerances based on a feature's geometry. It describes tolerance zones around a feature's theoretically exact location rather than a square tolerance zone. GD&T uses feature control frames and datums as reference surfaces to define tolerances for features. Common GD&T tolerances include circular runout, total runout, concentricity, and angular tolerances.

Uploaded by

parthiban
Copyright
© Attribution Non-Commercial (BY-NC)
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
You are on page 1/ 6

Geometric Dimensioning &

Tolerances

Geometric Dimensioning & Tolerancing


„ uses standard symbols to indicate tolerances
that are based on the feature’s geometry.
„ sometimes called feature based dimensioning
& tolerancing or true position dimensioning &
tolerancing
„ uses feature control frames to indicate
tolerance

G D & T Symbols

1
Understanding Tolerance Zones
„ Traditional plus/minus type of tolerancing describes a
square zone for acceptable locations.
„ GD&T describes a zone around the theoretically exact
location for the feature.

Basic Dimension
„ A theoretically exact
dimension used to
locate features in
GD&T
„ Basic dimensions
are untoleranced.

Datums
„ Datums are features
on the object that are
used as reference
surfaces from which
other measurements
are made.
„ Not every GD&T
feature requires a
datum.

2
Cylindrical Tolerance Zone

Circular Runout

Circular Runout
„ Controls single circular elements of a
surface
„ Controls circularity and coaxiality (two
or more features share a common axis)
„ Used to control wobbling motion
„ Measured by full indicator movement
(FIM) of a dial indicator

3
Total Runout

10

Total Runout
„ Provides combined control of a surface
element
„ Controls circularity, straightness, coaxiality,
angularity, taper, and profile or cylindrical
objects
„ May be used to control wobble and flatness
along with concavity or convexity of surfaces
perpendicular to a datum

11

Maximum Material Condition


„ Maximum material condition for a hole feature
is the smallest sized hole.
„ Maximum material condition for a shaft
feature is the largest shaft.
„ The maximum material condition modifier in a
feature control frame means that the
tolerance applies at max. material condition.
If the actual hole is larger than the smallest
allowable hole, a bonus tolerance can be
added to the stated tolerance value.

12

4
Maximum Material Condition

13

Angular Tolerances

Traditional methods for tolerancing angles require that angled surfaces


be very accurate near the vertex of the angle, but can vary more
along the length of the angled feature.

14

GD&T Angular Tolerance Zones

15

5
Concentricity

16

Summary
„ There are several methods you can use to
specify tolerances in a drawing.
„ Limit tolerances give the upper and lower
range for a dimension
„ Plus/minus tolerances give the nominal or
basic size and a plus and/or minus range for
the tolerance.
„ GD&T uses symbols to describe tolerance
zones based on geometric features.

17

You might also like