True Position not registering a result

[[Za...]]

I have some true position callouts that are giving me a result of 0.000000" instead of something greater than zero.

I've seen this in the past and I just want to know why it does this? Is it because I'm taking the true position of a circle instead of a cylinder?

Thank you as always for the help!

[[Er...]]

I could be mistaken but it looks like checking a circle to a Datum A only would be reporting the perpendicularity, which on a circle would be zero. It should be a cylinder which would then report the deviation of the Cylindrical hole to Datum A.

[[Za...]]

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I appreciate the help! Thanks

[[To...]]

Using datum A only will allow the X and Y to translate to its' nominal position, effectively reporting zero TP. If you measured a cylinder, then the axis deviation or perpendicularity would calculated, like previously mentioned.

Are there a group of holes sharing the same position? If so, you need to change the Position to a Best Fit Bore pattern (icon at top below the position label),,, Then select all of the circles. In the same window, you will leave Rotation and Translation best fit options checked.

[[Za...]]

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My issue was taking the TP of circles to just the one datum (The plane the features are on). I knew I've seen this before and I thought that I fixed them by making them cylinders, but I had never heard the explanation. It definitely makes sense now.

Thanks again for the help (I'm a repeat offender on asking questions in here 🤣 )

[[Ra...]]

Ya do what Tom Oakes said.

If it's a perpendicularity callout, use the perp function in calypso and use a cylinder.

If it's a position to a single datum like that, it needs to be a bestfit of a hole pattern (6x on the callout for example) evaluated at once.

If it's a position to a single datum and only a single hole, it's an invalid callout and you need to ask the engineer what they wanted.

[[SH...]]

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I think he misunderstood the drawing or something wrong in the drawing. If it is a one datum plane and cylinder , then why true position. If things are going this way,we can see the elimination of perpendicularly and parallelism in upcoming ASME standard.
Bore pattern can be called with respect to a plane?. I think it should be with the centre bore.
Can we tick the check box with out knowing FCF call out? He might not have MMB call out.

[[Ja...]]

What Tom said is correct. I occasionally see bores held to one datum (their parent surface) and every time I've asked what the primary concern was with said bore, I was always told "tilt." So, yeah, most likely what the engineer wants to see is axial tilt to the parent surface, or (drum roll) perpendicularity! I usually just drop in a perpendicularity characteristic, apply my feature and datum, click on the "comment" button and enter something like "True Position as Perpendicularity."

[[To...]]

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We really don't have all of the information. He could be referring to a lower tier of a composite true position. And, if it is the lower tier of a composite position, then a group of holes called to datum A are still allowed to translate and rotate regardless of MMB, which would not apply in this case.

[[Ch...]]

Position to one planer datum is totally legit in 14.5. Meant to control orientation and location. I wish more designers would use this strategy.

[[Za...]]

This is the callout if anybody is interested for discussion purposes 😃

[[Ch...]]

bonus to anyone who knows what Circle S means without google.


extra credit for knowing when it was obsoleted.

[[Da...]]

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Too late I already Googled it! But, I won't tell. 😃

[[Mi...]]

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What does "knowing the name, but not understanding the concept" get me?

[[SH...]]

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I know you are kidding eventhough, I added the photo. It is default condition....

IMG_20210107_200233.jpg

[[Ri...]]

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Then the holes must be evaluated together in a Best-Fit.

[[SH...]]

Only one plane, how location of best fit work?? Really interesting....

[[Ri...]]

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It is a fit to themselves.

[[Er...]]

Tom, as much as i agree with you that it is a fit to themselves, there is nothing locating the two holes to anything else. I still think the callout is flawed and the holes are designed to be located from some other feature as well. Afterall, the print shows a 1.428 basic from the center hole to the hole pattern. It doesn't make sense that these 2 holes don't have an additional position or location in X and Y. I would definitely ask for additional information as to what is needed.

[[Ch...]]

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What Tom stated is entirely accurate to how the print is written; However, Eric may have a point as well. The Circle S indicates that this is probably a pre-1994 print. From my understanding, using this position to one datum design strategy was not as common back then. Maybe we have a very forward thinking pre-1994 designer at work here, but I would be a little suspicious of design intent in this particular situation.

[[To...]]

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Spot on Eric. I was trying to answer the question with information on hand. Didn't even consider that we might be talking about an ancient drawing from my youthful days...LOL

[[Er...]]

Unfortunately, all too often I deal with prints like this. LOL

[[An...]]

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Best-Fit means aligning the 2 symmetry points and zeroing the symmetry point.
See attached.

Contribution_16_01_2021_1.pdf