Feature of Size (FOS) 2

[SpaciouS]

As I understand it, a FOS must satisfy all of the following:
[ul]
[li]Contains opposing elements or surfaces (regular or irregular shapes).[/li]
[li]Can be used to establish an axis, median plane, or a center point.[/li]
[li]Is associated with a size dimension.[/li]
[/ul]

Then you hear about the "Caliper Rule", where you should be able to measure or pick-up the feature with a pair of calipers (or 2 fingers).

My question is, what if, for example, you have a lens cell (for opto-mechanical design) with 3 tangential flexures 120 degrees apart about a common axis, and on those flexures you have raised pads which interface with the glass lens. These pad surfaces are arced and between the 3 of them they essentially form a diameter. Doe this constitute as a FOS (internal)?

I say yes. Even though the elements or surfaces are not "opposed" and you could not measure or pick-up the feature with a pair of calipers, you could measure or pick-up the feature with an expanding pin. Would this fall into the "irregular FOS" category?


Thanks,
Sean

 

[pmarc]

If I picture this correctly, my answer is yes - this is internal irregular FOS.

 

[SeasonLee]

Is this the one you are searching for?

http://www.ttc-cogorno.com/Newsletters/120201IrregularDatumFeatures.pdf

Season

 

[SpaciouS]

Season,

Yes thank you for that link. That's pretty much it...

Thanks,
Sean