True Position of a Diamond - Boundary Condition

[[Me...]]

Hello all,

I ran across something that I've never dealt with before: True Position of a Diamond with a note that says "BOUNDARY".

The call-out actually is https://imgur.com/a/CkAbzLb.

I asked for some clarification, and apparently there is a section in ASME Y14.5 (page 54-55 of the standard for 1994).

I somewhat understand it, but applying it (with MMC) in Calypso seems like a challenge (maybe I'm overthinking it).

Has anybody dealt with this that can help me out? Thanks.

[[Ca...]]

It's been a while since I've seen one of these, but I seem to remember that BOUNDARY implies that the tolerance for only exists INSIDE the nominals. I think I solved it with a best fit profile that had half the TP tolerance, and was checked as unilateral, with the tolerance being inside the feature.

I hope that makes sense, or someone else chimes in.

[[Me...]]

Hi Casey,

I believe that you are correct.

Take a look at the attached PDF and see if that aligns with what you are thinking.

I appreciate the input!

BOUNDARY EXAMPLE.pdf

[[An...]]

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[[Aa...]]

Not so fast, Andreas! The outer boundary on that second profile is incorrect. (U).026 puts the outer boundary 0.026 heavier than the true profile, when it should only be 0.013 heavier than the true profile. Also, there isn't really an inner boundary related to the DRF of the position FCF. (There would be a resultant boundary, but it definitely wouldn't be right at the true profile, as you've indicated.)

Andreas and Richard are pointing to "combined controls" (6.5.5 in 1994). The OP's print may or may not fall under that category, depending on how the print establishes the limits of size. If the diamond size is not controlled by a profile tolerance, but by directly applied size limits on the two widths, then the appropriate section is 5.10.1. The concept is really the same, but it's indication method is (in some people's minds) more simple, but less generically applicable.

[[Aa...]]

I used "outer" and "inner" to mean relative to the material, not the opening.

[[Me...]]

Here is a snapshot of the feature and its respective call-outs.

https://imgur.com/a/yJGcafi

[[Aa...]]

Boy, that's a little backwards. I always cringe when I see sharp-corner limit dimensions like that, because it leaves me in doubt about what they're trying to control. Why wouldn't they apply the control across the wall-to-wall widths? But based on your explanation, I would believe those size limits are supposed to establish the MMC.

The next logical question is: should the boundary be .0045"/side heavier than the basic size, or .00391"/side heavier than the basic size?

Put another way, are the +/- .002" tolerances across the corners intended to be the same as a .002" profile, or a .00141" profile? (The corners of a profile tolerance zone of a true profile with sharp corners are not radial in ASME the way they are in ISO.)

Wherever that boundary is supposed to be, you can accomplish it in Calypso if you have FFS. Apply a Profile characteristic to the diamond. It should be set to outwards to infinity or inwards to infinity. (I don't remember which--I only remember being confused by the translation from German.)

[[Me...]]

Thank you for the guidance.

I will use this information to have a discussion with the customer and go from there.

Cheers.