Profile of a plane to one datum that is a plane parallel to the profile feature?

[[Ga...]]

Unsure if I can share photos, I'll do my best to describe the situation.

First, I've been doing this for almost 6 years. In that time, I have never once had a good grasp on profile, and have mostly learned everything I know on the job from my mentor outside of taking Calypso basic and advanced at Zeiss in 2021 (meaning I may not understand all 'proper' technical terminology). This month is my first month without a mentor and I am now the 'senior' metrologist at my company with nobody to ask any Calypso questions to. I've deeply feared the day I will come across profile again, and of course our first big project after the staffing change has 5 profile callouts and only one with a full DRF of ABC. Any help explaining anything to do with Calypso 8.0 profile techniques would be greatly appreciated!! The new GDT engine makes even less sense to me than the old one. 

 

Here's the situation:

Print has a full DRF of A being a plane in XY, B being a line along Y, and C being a line along X. They want a profile of a plane that is parallel to datum A and the callout is to datum A only. I know that unfilled alignment elements refer to the BA, which is already comprised of the print DRF. However, I feel like if they wanted it to ABC they would have called it out as being to ABC instead of specifically A? Obviously a plane parallel to the measured feature is not going to constrain much and Calypso makes it clear that just datum A is insufficient. 

 

From what I've read here, it looks like I can use alignments and constraints to achieve this profile. Unfortunately, I don't really understand how to do that and I think I am missing basic information that would make the posts about this that already exist clearer to me. I have little (basically zero) experience with freeform, and even less experience with using alignments outside of a standard local alignment. I have seen programs written with constraints applied to radii <180° to get a better radius value, but I have never understood what that is doing. I am unsure if checking a translation/rotation XYZ constraint means it IS constraining that axis or if it is NOT constraining the checked axis. I think in this case I would want to constrain translation along X and Y and rotation around Z, but I don't even know where it would be appropriate to do that (Measurement plane? Datum plane? Geometry best fit alignment? Is it datum A that I would put into the geometry best fit alignment or the profile measurement plane? What is the air-speed velocity of an unladen swallow?)

 

I got blindsided with this huge expedited project Thursday of last week, and I have until the end of the first full week of January to make this CT program happen. Today's my last day in until Jan 5, so I am under a huge time crunch and don't have time to play around with this until I feel comfortable with it.

[[Ma...]]

Your profile callout to only datum A is just a parallelism - which should give you same result as your profile callout.

Are you working with ISO or ASME ( difference would be printed result ).

I think new GD&T should give you a result with only A used, but i think you can make it with alignments like this:

• make fully defined alignment ( ABC )
• use this alignment as your feature's alignment ( open feature and on right side there is usually choosed "base alignment"
• open evaluation tab
• check bestfit translation only in Z ( i think rotation in Z is useless )
• save this bestfit as an alignment
• use this bestfit alignment in your profile callout

And again - it should give you same result as parallelism

[[Ja...]]

I have a feeling I am making a big mistake by disagreeing with Martin. I am sure he will correct me, but if there is a basic dimension between datum A plane and the feature plane then profile will be different than parallelism. If the basic dimension is 5.000" and the distance between the two is 5.050", then your profile is going to be over 0.100"

Edited December 23, 2025

[[Lu...]]

Can you post a sketch of a tolerance? 

And features?

It can be hand drawn, no real data necessary 

[[RP...]]

Would this be relatable? 

The profile measurement changes based on the width of the .075, which is not a basic dimension.  I'm assuming the best fit compensates the width in the plane's vector?

[[Ma...]]

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Everyone can make a mistake - so was I when not considering base dimension from A as you did - thanks.
And in your answer you are right - it would be 0.100 if any of a measured and filtered point would be 0.05 away from base dimension.

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 i think if that dimension is not as base then different distance from A should not make any difference in profile result.

At least i hope 🙂

[[Je...]]

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, you're an extremely intelligent programmer, and your company is fortunate to have you on their team.  It's understandable to feel overwhelmed by the absence of your mentor and the demanding timelines we often face in manufacturing.

You've got this.

Having a trustworthy mentor is pivotal, but sometimes the most important phases of growth in our professional careers happen when those mentors are removed from the scene.

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Profile of a Plane Constrained to A Single Datum
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Let's look at the GD&T requirement first and then how to properly set up the profile characteristic in Calypso:

"They want a profile of a plane that is parallel to datum A and the callout is to datum A only."

As you figured out, this means that the Base Alignment should be assigning degrees of freedom to the profile characteristic.  You also were on point that Calypso has a tendency to assign constraint to any degrees of freedom that it can in a characteristic, and it uses the Base Alignment to fill in any missing constraints.

The best solution: While there are multiple ways in Calypso to solve this, a Geometry Best Fit (GBF) Alignment is your best option for making sure the Base Alignment doesn't assign unnecessary constraint.  Create a GBF and select the Datum A plane as the feature of reference.  Leave all evaluation constraints checked.  If you're concerned that this allows Datum A more constraint than it's due, there are ways to create tiered alignments that free up constraint (for example, z-rotation and x,y translation).  However, I don't think it will be necessary in this case.

Try that out and see if it's a viable option.

PS, feel free to reach out anytime you have questions.


 

[[Je...]]

edit: meant to say "this means that the Base Alignment should NOT be assigning degrees of freedom to the profile characteristic."