BeginnerTopic 11 of 102Manufacturing, Robotics & Systems
Geometric dimensioning and tolerancing
Symbols define form, orientation and location requirements.
In depth
GD&T (ASME Y14.5, ISO 1101) specifies form (flatness, straightness, circularity, cylindricity), orientation (parallelism, perpendicularity), location (position, concentricity) and runout using symbols, tolerance zones and datum references. Material condition modifiers (MMC, LMC) give bonus tolerance.
Key points
- Datum reference frame
- Feature control frame
- Position tolerance zone
ExampleA position tolerance of ⌀0.2 at MMC controls where bolt holes lie.
What is Geometric dimensioning and tolerancing?
Symbols define form, orientation and location requirements.
Why is it important to understand geometric dimensioning and tolerancing?
Geometric dimensioning and tolerancing describes form, orientation and position precisely, which is needed for parts that must assemble correctly.
What is a datum?
A reference feature used to set up measurement and define the position of other features on a drawing.
What is the difference between size tolerance and geometric tolerance?
Size tolerance controls how big a feature is, while geometric tolerance controls its shape, orientation or position.
How is Geometric dimensioning and tolerancing used in practice?
Typical applications include specifying the flatness of a machine table, controlling the position of holes in a mounting plate and requiring a shaft to be straight within a set amount for a bearing fit.
What should I learn before Geometric dimensioning and tolerancing?
Study "Limits, fits and tolerances" first (topic 10 of 102 in Manufacturing, Robotics & Systems). It covers the groundwork this topic builds on.
What are the key points of Geometric dimensioning and tolerancing?
Datum reference frame. Feature control frame. Position tolerance zone.
Can you give an example of Geometric dimensioning and tolerancing?
A position tolerance of ⌀0.2 at MMC controls where bolt holes lie.
What comes after Geometric dimensioning and tolerancing?
The next topic is "Metrology", which builds directly on this one.
How difficult is Geometric dimensioning and tolerancing?
It is classed as Beginner in Manufacturing, Robotics & Systems (topic 11 of 102). It is an entry-level topic. It relies only on basic school mathematics and the ideas introduced earlier in this discipline.