Flatness w/ Perpedicularity and parallelism redundant?

[Jieve]

Hello all,

If I have a cylindrical part with a hole bored through the middle (the shaft spacer sleeve again), does it make sense to spec a flatness tolerance on one face (datum face) and a parallelism tolerance on the opposite face with respect to the first surface if there is also a perpendicularity callout on the center bore, or is the flatness in this case redundant? The length tolerance is 0.4mm total, and i spec'd the flatness and parallelism at 0.1mm each. Seems the perpendicularity tolerance would limit the flatness of the first (datum) surface if the tolerance was tight enough. Am i right about this? Again, working to ISO.

Thanks!

 

[fsincox]

Control of the actual datum feature is not applied, simply by its use as a datum, so it is not redundant.
Frank

 

[pmarc]

Keeping it short, perpendicularity on the bore has nothing to do with flatness of primary planar datum feature. No matter whether it is ISO or ASME.

 

[Jieve]

Guys, thanks for the replies.

I realized that in all of the examples I was thinking of, I was imagining the surface with the flatness control to be inclined, and I was thinking of that inclination as the surface not being flat (although it actually was). After drawing a few simple pictures with wavy surfaces that still represented good parts this made sense.

Thanks!