New to me GDT call out

[RJT]

Quoting some plates that have a call out on the bottom surface (parallelism symbol) // .012/100 to surface A (which is the top surface) . The only thing that I can guess is the .012 flatness applies over 100 mm? The part is 400 mm square and 40 mm thick. I've never seen a limiter used like this, am I on the right track?

 

[lobust]

ISO or ANSI?

 

[RJT]

Good question, this as a joint venture of a Japanese and US company, so I'm not sure. Why will it matter?

 

[Imachine909]

It means to be .012 parallel over 100 to the A datmum.

 

[lobust]

Good question, this as a joint venture of a Japanese and US company, so I'm not sure. Why will it matter?

Because they are not identical and I am not familiar with ANSI enough to feel confident answering...

And as diplomatically as I can possibly state it, American metric drawings are frequently a minefield of mixed/conflicting standards that experience has conditioned me to be ultra cautious about checking such...

 

[Imachine909]

I see this one a lot which is very similar to your example. This on is based on diameter.

 

[Uncle_Buck]

Its possible to interpret that as meaning .012 parallel every 100mm segment, so you have 4 segments or zones. Edited from flatness to parallel

 

[Mhajicek]

Its possible to interpret that as meaning .012 flat every 100mm segment, so you have 4 segments or zones.

To the best of my knowledge, it's .012 flatness over ANY 100mm segment, so in theory you have an infinite number of overlapping segments. They wouldn't accept a part with creases or steps every 100mm.

 

[Uncle_Buck]

To the best of my knowledge, it's .012 flatness over ANY 100mm segment, so in theory you have an infinite number of overlapping segments. They wouldn't accept a part with creases or steps every 100mm.

They might not like it but that's what is theoretically possible by the callout. If they don't like getting what they ask for they should understand gd&t better so they can communicate what they want.

 

[Mhajicek]

They might not like it but that's what is theoretically possible by the callout.

Disagree. That's the "local flatness". If there's a violation in ANY span of the specified size, it's out. Large surface plates are often specified this way, and no one would accept one with steps.