However, the flatness of derived planes is usually only found in connection with the maximum material condition.
The flatness tolerance can, like the straightness tolerance, refer not only to real planes (Figure 2.), but also to derived planes (middle-, symmetry planes). It comes in useful if a feature is to be defined on a drawing that needs to be uniformly flat without tightening any other dimensions on the drawing.Ī feature control frame is attached to the surface with a leader or extension line, in this case the tolerance applies to a single nominally flat feature. Figure 1.- The Flatness Symbolįlatness is a common symbol that references how flat a surface is regardless of any other datum or features. Symbol: The flatness symbol is a parallelogram, so to speak a “ rectangle in an oblique view” specified in the left side compartment of the feature control frame. Often a flatness tolerance is necessary for reference surfaces. for clamping or support surfaces of workpieces, for dividing surfaces of housings or for sealing surfaces with flat seals. The limitation of flatness deviations is necessary for many geometric elements, e.g. It is always less than the dimensional tolerance associated with it. Flatness is applied to an individual surface and it does not need to be related to a datum. It is a straight forward geometrical condition of a surface in which all the points must be in one plane. What is FLATNESS?įlatness tolerance extends the straightness tolerance by one dimension. The standards which are famous for GD &T terms are of course the DIN EN ISO 1101 and ASME Y14.5M-2009 ).
For this reason is essential that these parts are designed by default with such important specification which in Mechanical Design Engineering is called FLATNESS. All the time when you want to make sure something is accurately closed/sealed the parts that are joined in your mechanical assembly product must have a specified restriction for how tight that closure must be.
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