Feature Control Frame
A geometric tolerance is specified in the feature control frame. The following elements are written in the feature control frame.
- a
- Geometrical characteristic symbol
- Write the type of geometric tolerance.
- b
- Diameter symbol (when needed)
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The geometric characteristics that need to be specified are as follows:
Area inside a circle on a two-dimensional plane:true position,concentricity
Area inside a cylinder in three-dimensional space:straightness,parallelism,perpendicularity,angularity, true position,coaxiality
Area inside a sphere in three-dimensional space: true position - c
- Geometric tolerance value
- 公差值。单位是the millimeter (mm).
- d
- Material requirement, common tolerance zone, etc.
- Typical indications include(maximum material requirement),(least material requirement), and CZ (common [tolerance] zone). Others includeand.
- e
- Priority datum
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The designer can specify as a datum the part that they want to prioritize as a reference. To specify multiple datums, write them in the order of priority (left to right).
Generally, designers determine the letter assigned to a datum in the order of priority—therefore, priority is generally described by alphabetical order.
