Co-datum B(M)-D(M)

[[Ju...]]

I am new here on this forum, but not new to GD&T. I’ve decided to post here because I could not find a satisfactory answer for my question. I searched this forum and I would like to piggyback on a different discussion I found here, but adjusted with my scenario.
What is the best way to take advantage of datum feature shift offered by B(M)-D(M) callouts, in Calypso?

I would like to know how B(M)-D(M) is calculated and how to use this datum feature shift?
Again, just to make myself very clear: I am not talking about bonus tolerances (offered by shown position), but about datum feature shift which come from B(M)-D(M)
For example on my added perpendicularity callout, how Calypso calculate any additional “wiggle room” provided by the MMB’s on the datum features B(M)-D(M)?
Or, on the shown profile, (again added by me to explain my question), how to take advantage in the Calypso software of the M’s - provided by B(M)-D(M) –
I am using ASME Y14.5-2009 standard.

[[Ch...]]

Might want to try "stepped cylinder"

Good luck !

[[Ju...]]

Do you know if this (co-datum shift issue) is covered into Capypso manual?
I cannot find anything, but I might not have the latest version of the manual.

Also I cannot find anything relevant on "stepped cylinder" discussion.

[[Ch...]]

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Pardon me, I meant 'step cylinder', what version are you on ?

[[Ju...]]

I am on Software Calypso version 2014 5.8.2 service pack 5.

I understand this:
"I created a step cylinder and used recall feature points, picked Datum B and datum D, to create my B-D Datum. I am now able to apply MMC on that B-D datum"
from a different discusson shown below, but I am interested how the math works and how Calypso is using the MMB's?
viewtopic.php?f=13&t=3699&p=24658&hilit ... tum#p24658


Otherwise stated: after I am creating the common axis, how MMB's are calculated from this common axis?
What are the values and how those values are driven for A(M) and for B(M).
I know the MMC value for A, I know the MMC value for B
I know the actual value for A, I know the actulal value for B.

What is the software doing with those numbers to get A(M)- B(M) in order to correclty use the datum feature shift?

[[Ju...]]

Just to push this discussion a little forward, I would like to ask you, from your CMM experience (regardless if it is with Calppso or not), do you think is better to have a functional gage/ maybe functional fixture available in order to be able to take advantage of the datum feature shift?

See the attachment for the concept and the note that "when establishing the datums, probing the part with the CMM can give the computer wrong information. Instead, probe the simulated datum reference"

So, applied to my case (and I know will have some practical limitation on my scenario) if the base alignment is done by probing the gage elements (two perfectly coaxial bushings made at MMC/MMB) you have a better chance of using the datum feature shift then if the base alignment is done by probing the actual cylindern / on the actula parts.

Am I correct?

If yes, then how would some skilled CMM programmer/ operator would do it? (again, I am not asking specifically to Capypso, but in general, lets say with your CMM software)

CMM fixture versus LSQ CMM algorithm - Copy.jpg

[[Da...]]

Bump,

if anyone knows, I'm interested too.

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[[An...]]

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In theory,yes!

But you,as a CMM-operator,have to do some hundred manual datum-rotations and also hundreds of CMM-runs
in order to achieve one precise result of perpendicularity.
Not very realistic procedure!

See attached.

Contribution_19_03_2021_1.pdf

[[An...]]

Some further information about datum rotation.
See attached.

Contribution_23_03_2021_1.pdf

[[Ni...]]

That print looks familiar. 😱 Brings me nightmares looking at it haha.
From what I remember, I was told stepped cylinder should be used for circular Datums shift. The center created from both datums would be the new datum.
Hopefully I wasn't wrong when using it on the program for that part! 😮