GD&T "Law"

Chip_M

Registered
Just had a new one thrown at me that I have never heard before and am hoping for confirmation or maybe clarification. had a customer inform me that if a CTQ dimension on a drawing is called out as a datum that all dimensions tied to this datum thru concentricity or true position must also be considered a CTQ per GD&T "law". has anybody else heard of this before
 

Miner

Forum Moderator
Leader
Admin
That does not make sense. I could understand the logic of the reverse (i.e., if a Position is a CTQ then the datums used in the Position callout would be important in establishing that Position), but I have never seen that stated anywhere as "GD&T Law." What industry are you in?
 

Chip_M

Registered
Plastic injection. It was a new one to me also. I was having a heated discussion with one of our customers when he threw it at me and why I put it out there in case it was a rule that I'm unfamiliar with. I've been using GD&T for more than 20 years and even though I don't consider myself an expert I never heard of this and wanted to know if there was a rule change, I didn't know about.
 

Miner

Forum Moderator
Leader
Admin
When researching this topic, I could find no search results on both CTQs AND GD&T in the same result. It was always one OR the other but never both. I even tried using Copilot AI with the same results. Sounds like your customer either made this up or is reading way too much into things.
 

optomist1

A Sea of Statistics
Super Moderator
Hi Chip, a screenshot of drawing would help further inform...I too have never heard of such a scenario...

Optomist1
 

Watton1440

Registered
This is just my assumption, but it sounds like he is confusing the simultaneous requirements rule of Y14.5 section 4.19.


If what you said is correct, then I believe he is in the wrong.
 
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