Flatness

Name: Flatness
Type: Form
Description: Controls the form of a flat (plane) feature.

Details
MMC Possible? No. Planes are two-dimensional, therefore are not features of size.
Bonus Tolerance Possible? No.
Measured from Datum(s)? No. Measurement is of actual feature compared to a perfect form of itself.
Perfect Form at MMC: Required.

Print
Callout on print: Feature control frame either on an extension line from surface or attached to surface with a leader line. Callout is shown in a side view of the plane.

Tolerance Zone: All points of a plane surface lie within a tolerance zone bordered by two parallel planes.

Measurement
Do not fixture using another workpiece feature. No datums are allowed with this tolerance.
Normally the best measuring methods include a CMM or a Flatness gage. A Flatness gage measures only the flatness of the feature, avoids datum fixturing.

Other
Notes: Size must be verified independently of the GDT measurement.
Before measuring or checking workpieces, let the workpieces cool.
Clean the workpiece and all gageing, fixturing, and measuring instruments.

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