Reported Nominals for Profile

[[Me...]]

Hello,
can anyone tell me how the nominals are calculated on a profile evaluation with datums?
I have basic dimensions on the drawing / model and they do not report as the same on results.
in fact the result nominals are not recognizable to the drawing or the measured feature actuals.
I'm using "Bilateral - one result" using alingments for "Primary datum" same as i would for true position.

TIA

-Dave

[[Me...]]

[[Fa...]]

Hi,
As far as I know, the coordinates are from the point on your surface that deviates the most from the target contour.

[[Te...]]

Those numbers have never made sense to me and I usually turn them off and report the actual BASIC a different way. Those number are usually helpful for position but for profile they make no sense.

Also just a heads up you should be breaking the datum features out and not using the alignment system as the primary datum. If you turn your form data on (ISO 5459) in the settings it only gets applied when you break out the Datum Features into each individual datum.

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True Position Profile correctly.JPG

[[Me...]]

Fabian,
you are saying even the nominals are reported as the point farthest from the target? I guess that makes sense if it's an envelope around the surface. It is not very useful data for the machinist to make an adjustment to.
Thanks for your input.

[[Me...]]

Ted,
based on what I understood Fabian to say I get why you don't use the output.
This part is the first time I've used profile to control location, as i said to Fabian the result would be worthless to a machinist.
I guess i will give them the basic dimensions in cartesian and let them decide whether they have a form / orientation or a location problem.
Thanks for the tip on ISO 5459, i thought as long as you had it on in the settings you were golden.
Thanks for the input.

[[An...]]

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The drawing is 1.5600 and the result of geometrical addition is: 1.5600.
See attached.

Contribution_17_04_2019_a.JPG

[[Me...]]

Profile is checking the surface itself, not the nominal location of the feature. The coordinates it's reporting is the location of the most out of tolerance point on the surface relative to your alignment. If you run another part odds are the nominal coordinates it shows will be different every time depending on where the worst profile measurement is.

[[Kl...]]

the entity is always in reference to a coordinate system
When a pattern is created by freeform surface 2 strategies are possible
- single point or
- scanning
Surface 1: shows regular pattern, single point measurement
Surface 2: not regular, scanning

For both ways CALYPSO calculates the foot point into the entity => local nominal. The vector calculation for local nominal and actual gives the local deviation. This is done for all all actuals. The extrem deviation gives the shown actual and nominal at report and the actual deviation.

If an element like cylinder is taken, the entity are the nominal of the cylinder which is related to a coordinate system. Therefore the location of the extrem deviation is always known.

With other words, Surface form is a multiple space point measurement and find the extrem deviation and report this result

[[Br...]]

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You can still do the "form datum" constraints in a secondary alignment. Sometimes you need to use secondary alignments. You might have a pattern of features that make up a single datum feature where some sort of best fit alignment is necessary. Just click on any feature in your alignment, click "Constraints", then click the button that says "Form Datum as per ISO 5459". make sure you have completed your alignment before pressing this. It will not affect any additions to the Alignment after you press it. You'll just have to press it again to update it.

[[Me...]]

I appreciate all the replies, it's becoming clear to me.
I was thinking in terms of true position in regards to the nominals because of the basic dimensions and that was confusing me.

[[Te...]]

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Brett,

Yes that is definitely another way to do it. I also think that sometimes it is easier to add the constraints and the outer tangential to a secondary alignment for certain alignments, especially if I need to rotate the alignment. I can do it for position (special button) in the characteristic but I think there is no special button for a profile.

[[Br...]]

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Yeah I guess the only purpose for the "Special" button is so that you can type in the XYZ values to establish the true position and then they can be output. Otherwise, I dont know why calypso cant just figure out that the tolerance zone is not Normal to the DRF and establish the proper Tolerance zone itself. With profile It does this for you(Thankfully!). So no need for the special button with Profile.

[[Ri...]]

Am I incorrect for creating alignments where the surface should exist and using that alignment?
The alignment created will be attached to the associated alignment.

By using the above method, I get values from a zero location. Then report Basics per the B/P.

[[Br...]]

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The problem Ted is talking about regarding this method is that Calypso just intersects the datum features for an origin if you don't modify the constraints. It doesn't reflect the way a true Datum Reference frame constrains each degree of freedom based on precedence, and how a datum simulator should behave.

The first thing you need to do is make sure you have the form datum option activated. Go to Extras>Settings>Measurement and select the "Form Datum" tab. Select Outer Tangential Element as the Evaluation method for Datum, and Check the box that says "Ref. Calculation as per ISO 5459".

Now, when you plug each datum feature into a characteristic, It creates constraints based on precedence and selects the Outer Tangential evaluation.

Ted's concern is that even with this activated, it will not do these calculations on secondary alignments on its own. You must open the constraints window and select "Form Datum as per ISO 5459" if you want to create your DRF properly.

Capture.JPG

[[Ma...]]

As suggested don't turn on positional result fro profiles. They are misleading

Notice the profile values (the first item in the report) are the same as the minimum point (second item). This is due to this point being the furthest away from nominal thus it is the one used in the calculation of the profile. This ‘T’ value (the distance of the point along the normal vector of the curve) is doubled and this becomes the profile result (0.0164 x 2 = 0.0329).

This value will change from part to part because the min/ max points will change part to part.

Mark