SEGMENT 7: DIMENSIONING & TOLERANCES
TOLERANCES
- Dimensioning - the rules and principles of size.
- Dimension Line - a thin line that shows where a measurement begins and where it ends.
- finish mark - surface-texture symbol, shows that a surface is to be machined, or finished.
- aligned system of dimensioning, the dimensions are placed in line with the dimension lines.
- unidirectional system of dimensioning, all dimensions read from the bottom of the sheet, no matter where they appear.
- Datums - points, lines, and surfaces that are assumed to be exact.
- Tolerance - permitted variance.
- Unilateral tolerances allow variations in only one direction from a design size.
- Bilateral tolerances allow variations in both directions from a design size.
- A basic hole system is one in which the design size of the hole is the basic size and the allowance is applied to the shaft.
- A basic shaft system is one in which the design size of the shaft is the basic size and the allowance is applied to the hole.
- The addition of this material, size, and shape information to an engineering drawing is known as geometric dimensioning and tolerancing (GD&T).
SECTION 7.1
-Notes and symbols give information
about the type of finish and materials
needed to make an object, and measure-
ments or dimensions must be as precise
as necessary to allow the manufacturer to
create the object.
-ASME and ISO standards closely con-
trol the dimensions and notes used in
dimensioning.
-Size dimension defines the size of each
piece; location dimension gives the size of
each piece as well as its position in rela-
tion to the other pieces.
-Why must variation in specified dimen-
sions for mating parts be limited?
To specify permissible variations in parts
to be manufactured, technical draw-
ings include geometric dimensions and
tolerances.
-Notes and symbols give information
about the type of finish and materials
needed to make an object, and measure-
ments or dimensions must be as precise
as necessary to allow the manufacturer to
create the object.
-ASME and ISO standards closely con-
trol the dimensions and notes used in
dimensioning.
-Size dimension defines the size of each
piece; location dimension gives the size of
each piece as well as its position in rela-
tion to the other pieces.
-Why must variation in specified dimen-
sions for mating parts be limited?
To specify permissible variations in parts
to be manufactured, technical draw-
ings include geometric dimensions and
tolerances.
OTHER KEY TERMS
Content Vocabulary
• dimensioning • dimension line • finish mark • aligned system • unidirectional system • datums |
Academic Vocabulary
• symbols • processes |