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Machine Trades Print Reading
LIMIT TOLERANCING
Success in manufacturing relies on the ability
to duplicate numerous parts to meet exact
specifications for assembly purposes. Specific
tolerances are required for parts to mate or
join properly. One way to specify a tolerance is
by indicating the limits of a dimension. LIMITS
are the maximum and minimum sizes allowed
for a dimension. Limits are beneficial when the
dimension’s value cannot exceed a maximum value
and cannot be less than a minimum value.
HIGH LIMIT
The HIGH LIMIT is the maximum value given
to a dimension. Under this condition, the high
limit is the largest acceptable dimension used for
manufacturing. See Fig. 4-14.
LOW LIMIT
The LOW LIMIT is the minimum value given to
a dimension. Likewise, the low limit is the lowest
acceptable dimension used for manufacturing.
When specifying upper and lower limits, the high
limit appears above the low limit. Refer to Fig. 4-14.
The difference between the high limit and the low
limit is the tolerance. The tolerance is the permissible
range of size for the dimension.
Calculating the Tolerance of Limits
Example 4-3:
Calculate tolerance for Fig. 4-14.
Formula for calculating work
Tolerance = High Limit – Low Limit
Solution:
Tolerance = 2.750 – 2.743
Tolerance = .007
SINGLE LIMIT
A SINGLE LIMIT tolerance is a variance on
a dimension that refers to either an absolute
maximum value or an absolute minimum value. The
abbreviation MIN (minimum) or MAX (maximum)
next to a dimension’s value indicates a single limit
tolerance. See Fig. 4-15. With a maximum limit, the
dimension cannot be larger than the specified value
and the minimum value (unspecified limit) can
theoretically be 0.00 (zero). With a minimum limit,
the dimension cannot be smaller than the specified
value and the maximum value (unspecified limit)
can theoretically be infinite. However, single limits
are only used when other geometry such as
dimensions or features control the unspecified limit.
Fig. 4-13. The basic size of a part is the theoretical size from
which tolerances are applied.
Fig. 4-14. Limits are the maximum and minimum acceptable
values for a dimension.
Fig. 4-15. A single limit dimension specifies an absolute
maximum or minimum value for a dimension.
TOLERANCES
BASIC SIZE
BASIC SIZE
TOLERANCES
HIGH LIMIT
LOW LIMIT