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Toleranced Dimensions Still Have Their Place.
Many companies are using a general
profile of a surface tolerance in place of the "old school"
general plus/minus tolerance. As pointed out in earlier Tips,
the advantages include:
- Less tolerance
accumulation
- Clear measurement
origins
- No tolerancing of points
in space that no one can find
- Uniform tolerance
zones
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Consequently, toleranced dimensions
are being replaced by BASIC dimensions. Although this approach
will be the standard practice in the future, toleranced
dimensions still have a place on most drawings. If, for
example, the general profile of a surface tolerance is relied
upon to control wall thickness, large variation could result.
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To reduce this
variation, a general wall thickness with a tolerance may
be used as a refinement of the general profile
tolerance. In this example, with a general profile
tolerance of 0.5mm and a nominal basic wall of 0.5mm,
without a wall thickness note, the wall thickness could
vary from 1mm to zero. |
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The general wall
thickness note as a refinement prevents this from
happening. This wall thickness dimension is a local size
that must be met at each cross section.
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