Flatness of specific regions

[kkeenn]

I have a rectangular plate where I need to specify a flatness tolerance on an area located 1.5" from the long ends (out of 40"). In the past when I specified flatness I've always specified from a-b but without a feature to associate a and b with I'm lost.


A little illustration where the x regions need to hold the tolerance

|-----------------|
|xx xx|
|-----------------|

 

[dingy2]

ASME Y14.5-2009 reflects the use of chain line boundaries on the surface using basic dimensions to depict the area requiring flatness. I don't know if your CAD software supports chain lines though.

Hope this helps

Dave D.

http://www.qmsi.ca

 

[pmarc]

I am with Dave on this.

I believe Y14.5 is not giving exactly appropriate example that you could use, but if you have access to the standard, take a look at figs:
- 4.29(a) in 1994 edition or
- 3.9(a) in 2009 edition.

Despite the fact that these figures are showing how datum target areas should be dimensioned, you could just do the following:
- replace datum target symbol by flatness FCF;
- add arrow to the end of the leader line;
- add basic dimensions for width and length of the areas controlled by flatness callout.