Rant

I have engineers here that have basic dimensions to control true position callouts-and they have true position callouts on those basic dimensions also!! They got upset cause i told them it makes no sense.. I have a hole with a TP .005 to A and B, and i have basic dimensions from A and B and then TP .004 of these dimensions to A.. How does that make sense?? how am i supposed to even inspect that ...but what do i know!!

AM I WRONG HERE???

FXSergiy over 3 years ago

If possible, give me a picture, please
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bfire85 over 3 years ago

I have engineers here that have basic dimensions to control true position callouts-and they have true position callouts on those basic dimensions also!! They got upset cause i told them it makes no sense.. I have a hole with a TP .005 to A and B, and i have basic dimensions from A and B and then TP .004 of these dimensions to A.. How does that make sense?? how am i supposed to even inspect that ...but what do i know!!

AM I WRONG HERE???

Yeah, you're going to have to post a snapshot.
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russell dunham over 3 years ago

Most of the time I see this is when they are trying to control perpendiculartiy. I have seen this over and over on thin sheet metal 0.6 - 1.5mm thick material.
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A-machine-insp over 3 years ago

I second (or third or fourth) a snapshot. I had a response typed out then I reread your post and saw the part about GD&T on the basic dimensions.
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pcdmisstudent over 3 years ago

Snapchat please
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Schrocknroll over 3 years ago

I think this is the part that is confusing.

they have true position callouts on those basic dimensions also

Position callouts are to features, not dimensions. A screenshot, picture, or even a hand drawn depiction may help us be sure what your question is.
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Disal over 3 years ago

okay so i can't post the drawing cause i haven't quite figured out how to cover what shouldn't be shared, but this is what i mean. i didn't draw the B datum

Attached Files
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DAN_M over 3 years ago

What is Datum -B-? That is the missing piece of info I need in order for me to be able to share my 2cents
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Disal over 3 years ago

What is Datum -B-? That is the missing piece of info I need in order for me to be able to share my 2cents

it's actually the plane where the hole lies on. I'm not too talented lol. but the Basic dimensions are off of centerline to A
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DAN_M over 3 years ago

With -B- as the plane that is perpendicular to the holes, then this is a "legit" callout (poor attempt at making a composite dimension). It certainly isn't how I would draft this, but it is mathematically feasible.

The hole can be within 0.005 to A|B (diametric tolerance zone)...AND it can simultaneously be within a 0.004 radial T.P. (since only one axis is called out its a ±0.002 of that hole location rotated to the the hypotenuse so 0.1517±0.002) back to -A-.

Yes, if the 0.004 was at high limit then you'd most likely be blowing the 0.005 T.P...but it could still work.
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