X only and Y only True Position Question

[[Si...]]

Image attached shows right side Hole called out for X and Y Axis positions. My Characteristic is setup normally for the datums except I select X only and Y only rather than the normal options. Is this correct? I ask because I will get a pass result for X but a fail for Y. The Y measures 0.2245 ( max .025 ). Now If i select the normal default eval for positions, the result lowers to 0.040 which still fails but is much lower.

Why is this? Why such a big number jump. I dont know how to explain it to the engineers. Just just say, the CMM is wrong. What am I doing wrong?

2022-05-11 12_10_10-81-4523.pdf - Adobe Acrobat Pro DC (64-bit).png

[[Mi...]]

Make sure the coordinate system generated by the position characteristic is actually oriented the way you're expecting it to. You may have to rotate it with the special button.

Also did you only make the typo in your post? or did you possibly make the same one in your program?

Tolerances in the image are 0.25 and 0.0125, not 0.025... maybe it's that simple. We've all made that mistake.

[[Si...]]

.0125, Yes typo . The thing is when I select X only and Y only. The Y which is both Holes same line, is Zero x 3 ( x and Z greyed out ) and Y is also the correct number with X and Z as Zero.

So im pretty sure I am correct but its the number jump that im trying to figure out.

If I remove X from the characteristic, its 0.22 .. If i add it back in, its 0.040

[[Si...]]

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Rotate with special button. I know of the Button, but rotate ? How would I do that, does it affect the CPs? and CGs?

[[To...]]

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Using the Special button inside a true position, only changes the values and relationships to the DRF. It doesn't effect any navigation. Not sure what CG is. This modification is often required when the feature is not on the same same plane as the datum feature(s). If datum A is the top plane and the slot is perpendicular to the top plane, I wouldn't expect to need to do any rotations.

[[Si...]]

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Clearance Plane and Clearance Group (CG and CP)

Soo overall, I set it up right? the 4 pad surfaces are datum A which I should've mentioned.

[[To...]]

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lol I was thinking that's what you might've meant.

Where is Datum B?

[[Ma...]]

Because of missing diameter sign you can select rectangle tolerance type.

[[Si...]]

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Datum B is located on the two left Pads, the left walls of each so its two surfaces to make up B.

[[To...]]

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Typically, with 2 separate callouts, you would use the "X only" for one and the "Y only" for the other. Rectangular would apply X and Y simultaneously.

[[To...]]

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How are you building Datum C? That is probably influencing the Y location for any ABC DRF.

[[Ja...]]

I have had this problem before. I just left it as diametrical X and Y because it was in spec and if that is in spec then it is inspec in Y only as well. I did not find a reason for it. Here is the post about it. viewtopic.php?t=860

[[Si...]]

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Its built as a slot, default setup ( 5 and 3 Points )

[[Ja...]]

What if you create an alignment to match your DRF. Create a theoretical feature recalling the original and change the alignment to the DRF alignment. Then use result element to get the Y offset multiplied by two. I haven't tried this so it might not be right.

[[Si...]]

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Ok, This helps. So its the Base Alignment. Pretty much as you said in your post. My Part alignment and Zero is same as drawing call out and nominals are all correct. So the X is set to X only and the Y should be Diametrical and not Y only then? Which is why I get a much smaller ( accurate) Number?

[[To...]]

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Ok. A slot will act like a circle in this case and not negatively influence the Y origin. Because there are perpendicularity requirements of C to A and B, I assumed you may have created a symmetry plane or a symmetry construction with 2 planes.

[[Ma...]]

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OK, but in drawings they can combine them together to have only one - so if this case happens, then as i said

[[Ri...]]

Use "Rectangular" instead of "Diametral".

Not Diametral or Cylindrical True Position 2.jpgNot Diametral or Cylindrical True Position.jpg

[[Je...]]

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Is this your datum reference frame? If so, how are you defining the slot in Calypso (symmetry of the slot's two circles, symmetry of the slot's two planes, etc.)? P.S. I made this illustration with the most advanced CAD software known to man, Microsoft paint. PPS., this doesn't have anything to do with your problem. It looks like you figured that out. I'm just curious.


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[[Da...]]

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Thanks Jeff, that's also how I imagine it.

I'm not being helpful probably, but if that's the case, then datum C in the lower FCF isn't doing anything:

[[Je...]]

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I agree, Dane. Datum C doesn't control anything in the lower position FCF.