About GD&T
What is GD&T?
Geometric
dimensioning and tolerancing (GD&T) is an international language
that provides clarity in drawing specifications and interpretation.
The proper use of GD&T will reduce vague drawings, and the resulting
controversy, guesswork and assumptions they cause throughout the
manufacturing and inspection process.
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What
are the benefits of using GD&T?
Geometric tolerancing encourages a dimensioning philosophy called
"functional dimensioning" which defines a part based on
how it functions in the final product. It also works well with "simultaneous
engineering," a process where design is a result of input from
marketing, manufacturing, inspection, assembly, and service. This
results in better products at lower cost.
- GD&T
Improves Communication
It provides uniformity
in drawing specifications and interpretation. It reduces controversy,
guesswork and assumptions so design, production, and inspection
all work in the same language.
- GD&T
Provides Better Product Design
It provides designers with the tool to "say what they mean,"
and by following the functional dimensioning philosophy.
- GD&T
Increases Product Tolerances
Under certain conditions, it provides "bonus tolerance"
for manufacturing. Through functional dimensioning tolerances
are assigned to the part based on its functional requirements
which often results in a larger tolerance for manufacturing.
GD&T eliminates
the problems that result when designers copy existing tolerances,
or assign tight tolerances, because they don't know how to determine
a reasonable (functional) tolerance. [Krulikowski, Alex, Fundamentals
of Geometric Dimensioning and Tolerancing, 2nd Edition. Albany:
Delmar 1998.]
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How
does GD&T save money?
Vague
drawings lead to errors that become more costly to an organization
at each stage of the product development process. If found at the
design stage, a vague drawing can be corrected for a few dollars.
In the model shop, it can cost hundreds of dollars. However, once
a vague drawing gets to production, the expenses escalate quickly.
Gaging, tooling, and scrap costs can bring the expense to several
hundreds of thousands of dollars.
The proper
use of geometric dimensioning and tolerancing will reduce:
- Drawing
revisions
- Gaging costs
- Scrap costs
- Design time
- Disputes
over drawing interpretation
- High manufacturing
costs
Using GD&T
correctly improves productivity and will save your organization
time and money. Learning to interpret and apply GD&T properly
will help you and your company:
- Save money
at the design stage
- Enable global
sourcing
- Reduce drawing
errors
- Increase
productivity
- Increase
part tolerances
- Assure that
mating parts will assemble
- Eliminate
scrap
- Improve
inspection accuracy
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Why
is it important to receive proper GD&T training?
GD&T
is a complex language. As with any language, it must be specified
and interpreted correctly to communicate well. Improper implementation
of geometric tolerancing on drawings can cost your company money.
However, the right training can provide your employees with an understanding
of GD&T and its correct application on the job.
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How
does GD&T compare to coordinate tolerancing?
Coordinate tolerancing has several shortcomings when compared
with geometric tolerancing, some of those are:
- Square
tolerance zones
GD&T eliminates square tolerance zones through the use of
cylindrical tolerance zones. The additional tolerance gained can
reduce manufacturing costs.
- Fixed-size
tolerance zones
GD&T eliminates this shortcoming and provides an additional
tolerance that reduces manufacturing costs.
- Ambiguous
instructions for inspection
GD&T eliminates ambiguous instructions through the datum system.
This allows the designer to communicate the appropriate method
of part setup to the inspector.
GD&T communicates
precisely and efficiently. Take a look at how a drawing with coordinate
tolerancing compares to a drawing with the same level of completeness
using GD&T. Click on either drawing for a larger view.
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Drawing
using coordinate tolerancing
|
Drawing
using GD&T
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Read more
about it—
Read more about
GD&T and how it will help your organization save money through
better communication and increased productivity:
GD&T
Resources (Including technical papers that discuss GD&T)
What
is GD&T?
A
GD&T glossary
"The
Tao of Tolerancing," by Alex Krulikowski (ETImail Volume
1, Issue 5)
ETI Provides More GD&T Training Options Than Any Other Company
Request a training quote
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