Coaxial holes

I have attached a call out below. What would be the best way to report this out. They are 2 cylinders in line about .250” long each with a 2” space in between. I’ve tried to
1. level and origin on one then report the TP. Of the other
2. 3D best fit both cylinders trans and rotate and report of both cylinders using worst end of axis.
3. using geo-tol by selecting both cylinders with no datum

all of these came up with different results. Which is the best way? Any of these 3 or maybe some different ways?

Should both holes be reported out or just the one? Because technically one becomes datum in way.

Attached Files

constadin over 3 years ago

Best thing to do for me... Define your Datums A B C fllowing the drawing, take 2 cylinders and create in Geo-Tol the exact composite TP callout as shown in the photo.
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DAN_M over 3 years ago

I do not understand the GD&T.

"2 coaxial holes"..? "Is there a tolerance? What is to be coaxial to what and within what tolerance range?" would be the questions I'd ask the design authority.

Also agree with others, dropping the -A- on the lower portion doesn't make sense. TP needs datums.
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vpt.se over 3 years ago

Use datum A for the lower segment? PC-DMIS needs datums and the lower segment needs the datum sequence to match the upper segment.
I'd go with A for the lower segment.

EDIT: Wrong!
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Neil Challinor over 3 years ago

constadin has the correct approach. It is composite position of a pattern of holes. The upper segment controls the relationship of the whole pattern to the datums and the lower segment is the relationship of the features within the pattern to each other - essentially concentricity between the two holes.
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Neil Challinor over 3 years ago in reply to vpt.se

NO. Adding datum A to the lower segment would add an orientation constraint between each hole and datum A - see my post below ↓
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Schlag over 3 years ago

Well done MIke.
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Mike Ruff over 3 years ago

To me this is an understanding of what the customer wanted and then they used an illegal callout ( in Y14.5 anyways ) . The bottom portion of a composite has to have the exact DATUM STRUCTURE or lack of . A-B-C- TOP A-B-C- BOTTOM IS Legal. A-B-C TOP / A-B- BOTTOM is legal. A-B-C TOP / A bottom is legal. A-B-C- TOP / No datums on bottom is not legal. I don think you can just drop the A of the bottom.Now 2 separate callouts would be fine, but composite isn't. I'm going with VPT.SE on this one.

In ASME Y14.5-2009, this is allowed
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Neil Challinor over 3 years ago

Thank you Mike Ruff , you beat me to it. It is also allowed in ASME Y14.5 2018 - section 10.5.1 (page 184)
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Jay_Q over 3 years ago in reply to Neil Challinor

I went with the geo tol option. But am I correct that I select both holes for the lower portion of the composite and report it out showing both?
The customer says I should only be reporting one hole. But I don’t think you can do that with geo tol.

Also what would be the legacy equivalent of achieving this result?
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vpt.se over 3 years ago in reply to vpt.se

Is PC-DMIS able to handle TP with no datums now? Earlier, you had to have a datum (usually the surface the holes were located in).

Or is this only applicable to composites?
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