Material Conditions; Datum Reference Frames - Autodesk 057B1-41A111-1001 - AutoCAD LT 2010 User Manual

Material Conditions

Material conditions apply to features that can vary in size.
The second compartment contains the tolerance value. Depending on the
control type, the tolerance value is preceded by a diameter symbol and followed
by a material condition symbol.
Material conditions apply to features that can vary in size:
At maximum material condition (symbol M, also known as MMC), a feature
contains the maximum amount of material stated in the limits.
At MMC, a hole has minimum diameter, whereas a shaft has maximum
diameter.
At least material condition (symbol L, also known as LMC), a feature contains
the minimum amount of material stated in the limits.
At LMC, a hole has maximum diameter, whereas a shaft has minimum
diameter.
Regardless of feature size (symbol S, also known as RFS) means a feature can
be any size within the stated limits.

Datum Reference Frames

The tolerance values in the feature control frame are followed by up to three
optional datum reference letters and their modifying symbols.
A datum is a theoretically exact point, axis, or plane from which you make
measurements and verify dimensions. Usually, two or three mutually
perpendicular planes perform this task best. These are jointly called the datum
reference frame.
The following illustration shows a datum reference frame verifying the
dimensions of the part.
426 | Chapter 9 Annotate Drawings