Tolerancing: Difference between revisions

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[[File:Tolerancing Annotated Design Model.png|thumb|left|GD&T 3D annotations]]
'''Tolerancing''', Geometric dimensioning and tolerancing (GD&T) means specification of permissible limits/deviation of dimensions. Here we're talking strictly about geometric tolerances: a real-world error of shape, size, location, orientation in a relation to the designed ideal.
[https://en.wikipedia.org/wiki/Geometric_dimensioning_and_tolerancing Geometric dimensioning and tolerancing] (GD&T) means the specification of permissible limits/deviation of dimensions. Here we're talking strictly about geometric tolerances: a real-world error of shape, size, location, orientation in relation to the designed ideal.


There's also a distinction between the terms "limits and fits" and "geometric tolerances and surface conditions".
There's also a distinction between the terms "limits and fits" and "geometric tolerances and surface conditions".
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== Standards ==
== Standards ==


There are 2 ANSI/ISO standards:
There are 2 ANSI/ISO standards:


* ISO 1101 / ASME Y14.5 Stating and interpreting Geometric Dimensions and Tolerances (Definitions and symbols) [http://www.sharifcadcam.ir/uploaded/2e22f9ef-dfc5-47bc-a126-cc51e9686c4f.pdf [1]]
* ISO 1101 / ASME Y14.5 Stating and interpreting Geometric Dimensions and Tolerances (Definitions and symbols)
* ISO 16792 / ASME Y14.41 Model-based definitions (CAD data) 3D model presentation and geometric dimensioning and tolerancing [http://gost-snip.su/download/asme_y14_412003_digital_product_definition_data_practices [2]]
* ISO 16792 / ASME Y14.41 Model-based definitions (CAD data) 3D model presentation and geometric dimensioning and tolerancing


ISO 16792 is a part of "Geometrical Product Specification" (GPS) which defines dimensional and geometrical tolerancing, surface properties and the related verification principles, measuring equipment and calibration requirements including the uncertainty of dimensional and geometrical measurement.
ISO 16792 is a part of "Geometrical Product Specification" (GPS), which defines dimensional and geometrical tolerancing, surface properties and the related verification principles, measuring equipment and calibration requirements, including the uncertainty of dimensional and geometrical measurement.


* [https://www.iso.org/files/live/sites/isoorg/files/archive/pdf/en/gps_toc_.pdf GPS Table of contents]
* [https://www.iso.org/files/live/sites/isoorg/files/archive/pdf/en/gps_toc_.pdf GPS Table of contents]


There's also ISO 10303 (informally "STEP") which defines the file format for exchanging product and manufacturing information which is sourced from model-based definitions.
There's also ISO 10303 (informally "STEP"), which defines the file format for exchanging product and manufacturing information, which is sourced from model-based definitions.


== Approaches ==
== Approaches ==


There are two approaches to specifying product and manufacturing information (PMI).
There are two approaches to specifying Product and Manufacturing Information (PMI).


* The legacy approach (Traditional) of producing 2D drawings with GD&T symbols
* The legacy approach (Traditional) of producing 2D drawings with GD&T symbols. In some industries, this approach is also referred to as Technical Product Documentation (TPD). How this is achieved with FreeCAD is described in [[TechDraw_Geometric_dimensioning_and_tolerancing|TechDraw Geometric dimensioning and tolerancing]].
* The modern 3D approach (MBD) which embeds GD&T data into the model and produces drawings with GD&T symbols
* The modern 3D approach Model-Based Definition (MBD) which embeds GD&T data into the model and produces drawings with GD&T symbols.


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* [https://forum.freecadweb.org/viewtopic.php?t=15497 Geometrical tolerances] - User feature request (2016)
* [https://forum.freecadweb.org/viewtopic.php?t=15497 Geometrical tolerances] - User feature request (2016)
* [https://forum.freecadweb.org/viewtopic.php?f=10&t=22072 GD&T Workbench for FreeCAD] - A workbench for FreeCAD 0.16 (2016)
* [https://forum.freecadweb.org/viewtopic.php?f=10&t=22072 GD&T Workbench for FreeCAD] - A workbench for FreeCAD 0.16 (2016)
* [https://www.forum.freecadweb.org/viewtopic.php?f=9&t=35392 TechDraw balloons] - A general purpose TechDraw Macro which can be used to place GD&T symbols on a TechDraw page (2019)
* [https://www.forum.freecadweb.org/viewtopic.php?f=9&t=35392 TechDraw balloons] - A general-purpose TechDraw Macro which can be used to place GD&T symbols on a TechDraw page (2019)
* [https://forum.freecadweb.org/viewtopic.php?f=35&t=35887 ISO 1101: 2017 Geometric Tolerancing Standard] - A link to the ISO 1101:2017 PDF file (2019)
* [https://forum.freecadweb.org/viewtopic.php?f=35&t=35887 ISO 1101: 2017 Geometric Tolerancing Standard] - A link to the ISO 1101:2017 PDF file (2019)
* [https://forum.freecadweb.org/viewtopic.php?t=42426 Geometric Dimensioning & Tolerancing] - Developer proposing contributions (2019)
* [https://forum.freecadweb.org/viewtopic.php?t=42426 Geometric Dimensioning & Tolerancing] - Developer proposing contributions (2019)
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== Tutorials and learning materials on GD&T ==
== Tutorials and learning materials on GD&T ==


* [https://www.youtube.com/watch?v=P5GT9ZSRYl0 Brief introduction (Video)]
* [https://hackaday.com/2018/10/04/how-precise-is-that-part-know-your-gdt/ How Precise Is That Part? Know Your GD&T]
* [https://hackaday.com/2018/10/04/how-precise-is-that-part-know-your-gdt/ How Precise Is That Part? Know Your GD&T]
* [https://www.youtube.com/watch?v=-3tN7KvDUjQ GD&T for beginners | step by step approach to do gd&t for mechanical drawing]
* [https://www.youtube.com/watch?v=-3tN7KvDUjQ GD&T for beginners | step by step approach to do GD&T for mechanical drawing (Video)]
* [https://www.youtube.com/c/StraightToThePointEngineering/videos?view=0&sort=da&flow=grid Straight To The Point Engineering (Video tutorials)]



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Latest revision as of 09:12, 8 August 2022

GD&T 3D annotations

Geometric dimensioning and tolerancing (GD&T) means the specification of permissible limits/deviation of dimensions. Here we're talking strictly about geometric tolerances: a real-world error of shape, size, location, orientation in relation to the designed ideal.

There's also a distinction between the terms "limits and fits" and "geometric tolerances and surface conditions".

Standards

There are 2 ANSI/ISO standards:

  • ISO 1101 / ASME Y14.5 Stating and interpreting Geometric Dimensions and Tolerances (Definitions and symbols)
  • ISO 16792 / ASME Y14.41 Model-based definitions (CAD data) 3D model presentation and geometric dimensioning and tolerancing

ISO 16792 is a part of "Geometrical Product Specification" (GPS), which defines dimensional and geometrical tolerancing, surface properties and the related verification principles, measuring equipment and calibration requirements, including the uncertainty of dimensional and geometrical measurement.

There's also ISO 10303 (informally "STEP"), which defines the file format for exchanging product and manufacturing information, which is sourced from model-based definitions.

Approaches

There are two approaches to specifying Product and Manufacturing Information (PMI).

  • The legacy approach (Traditional) of producing 2D drawings with GD&T symbols. In some industries, this approach is also referred to as Technical Product Documentation (TPD). How this is achieved with FreeCAD is described in TechDraw Geometric dimensioning and tolerancing.
  • The modern 3D approach Model-Based Definition (MBD) which embeds GD&T data into the model and produces drawings with GD&T symbols.
Traditional MBD
3D models with 2D drawings containing GD&T/PMI 3D model with embedded GD&T/PMI
Human-readable Human- and machine-readable
Relies on human interpretation Relies on an automated process
Labour-intensive Automated
Multiple files Single data model
Manual synchronization between CMM/CAM/CAI software Single source of truth

Existing software

Implementation so far

Forum threads

Tutorials and learning materials on GD&T