0019// General Tolerance for Straightness and Flatness -- ISO-2768-2
Do you familiar with table shown below?
You can find this table in ISO-2768-2 table 1. This table is general tolerance table for straghtness and flatness. When the drawing notes or tittle block specified ISO-2768fH, that implied all the feature of size, location and some of the geometrical characteristic are controlled by this standard.
However, some of the user not sure how to select a correct nominal lengths. So, this week we will discuss about how to select nominal length.
Example for Flatness:
Consider we have a turbine blade which called ISO-2768fH in drawing notes. Then, we want to know the flatness which govern the highlighted surface (red shaded)
First step, based on drawing notes, we know tolerance class is H. Second step, we need to know longer lateral length of the surface. Basically, longer lateral length of the surface is the length for longest possible straght line you can draw on the surface.
In this example, longest possible length is 157mm. Based on the table,
We known that, this surface controlled by 200 micron flatness .
Example for Straightness:
Consider we have tungsten rod which called ISO-2768cL in drawing notes. Then, we want to know the straightness of the rod.
For straightness is simple, based on drawing notes, this rod control by class L and the nominal length is 32mm (by specs).
Based on table, we known that, rod's feature axis controlled by 400micron straightness .
return 0;
