True Position of non-circular features

[spmoore]

Hi all,

I am having a hard time determining how to dimension a "T" shaped hole feature that is in a round stamping.

The "T" feature's location can float relative to the disc's center more freely as the diameter of the disc decreases. I want to be able to descibe this. True position seems like the right GDT. I have considered creating a theoretical datum point that is located at the "perfect" true position and references basic X and Y distances from edges of the feature. Seems to go against the spirit of GDT. Other than this I'm at a loss for another solution.

Any advice can be sent to steve.moore@paslode.com

Thanks.
Steve

 

[TheTick]

On the surface, that sounds OK to me. Just add MMC to the datum callout for your "disc center" diameter (assuming it is a positive projection).

 

[Hydroformer]

Can you define the T-shape as a 4-way datum and tolerance the position of the circular disc (LMC) ?

*Without data, you're just another person with an opinion.*

Hydroformer

 

[Tunalover]

The size (profile) and position of any bounded irregular feature can be controlled using a combination of profile tolerance and postional tolerance. The positional tolerance feature control frame should have the word BOUNDARY below it. In this case all dimensions pertaining to the feature would be basic. See for example Effective Training Inc.'s ULTIMATE POCKET GUIDE: Geometric Dimensioning and Tolerancing by Alex Krulikowski.


Tunalover