- [Instructor] Several simple steps will help you gain
an understanding of the meaning
of Geometric Dimensioning and Tolerancing notation.
A good place to start is by reviewing
the geometric control symbols
and understanding the geometry they control.
Next, understanding the use of datum as reference points
will help with fixturing parts from manufacturing
and verification.
Finally, it is important to understand how to read
feature control frames and interpret modifier symbols.
There are many websites and reference guides
that can serve as useful in-depth resources
for this information.
When learning how to read
Geometric Dimensioning and Tolerancing symbols,
it can be useful to understand how they differ
from traditional plus/minus tolerancing.
In the simple example shown here,
a 75 millimeter hole is positioned in a plate.
The diameter of the hole can vary between 74 millimeters
and 76 millimeters.
The position of the hole can vary
between 99.5 and 100.5 millimeters in one direction
and 109.5 and 110.5 millimeters in the other direction.
This position variation creates a tolerance zone
that is a one millimeter square.
The same hole when tolerance
using Geometric Dimensioning and Tolerancing rules
has a center located exactly 100 millimeters from one side
and 110 millimeters from the other side of this plate.
But the center of the physical hole can vary
from the ideal location anywhere within a one millimeter
in diameter zone.
In this example, the ideal position of the hole
is represented by the 100 millimeter
and 110 millimeter position dimensions,
and the tolerance of the whole position
is defined by the feature control frame.