MMC on datums

[ja500]

Here is the MMC problem!

The 2 tolerances are also shown as failing....but on closer inspection one tolerance does fail but the other tolerance fails BUT the deviations shown in qualify PASS the guage shown.

If these tolernaces are viewd in 'Insight then the same deviation are display and the guage fials but it shows the deviations as a PASS.

A component has the datums set up and tolerances applied.

The issue is arising where MMC is being applied to the datum. In this case datum B.

If this datum PASSED then there isn’t a problem all gauges are reported as expected.

BUT

If datum B FAILS then any corresponding holes tolerances that contain MMC that are called out against this datum B FAIL.

Because the MMC against datum B has failed then the gauges applied to this are measured to RFS.

Some of the holes now measured to RFS are within tolerance but are still displayed as FAILED.

Is this what you would expect to happen?

The tolerances that are applied are as folllows

The two guages that the issue is being seen on are as follows.

Feature datum B has the following tolerances applied to it

POS|DIA0.0005(M)|A

DIA -0.000 +0.003

FEATURE 1 (hole Pattern)

POS|DIA0.016(M)|A|B(M)

DIA -0.000 +0.003

Both these tolerances fail

'Datum B' should fail as the tolerances have not been acheived'

'Feature 1 (hole Pattern)' also fails even though the position of the holes are shown as 'PASSED' (but this is now to RFS not MMC as datum B failed)

I Then carried out a couple of tests the results are as follows -

TEST 1
I ONLY removed the MMC callout from the 'FEATURE 1 (hole Pattern)'

original POS|DIA0.016(M)|A|B(M)

changed to POS|DIA0.016(M)|A|B

The feature now PASSES

TEST 2

I ONLY changed the 'DATUM B' callout so that 'DATUM B' would pass.

original POS|DIA0.0005(M)|A

changed to POS|DIA0.007(M)|A

Both 'DATUM B' and 'FEATURE 1' guages PASS.

Is this what you would expect to happen with an MMC call out?
If the Datum B fails and has an MMC callout, should ALL other tolerances that use this tolerance also FAIL?

 

[desertfox]

Hello ja500

As my crystal ball is in for its annual service is there any chance you could upload a file which shows us what it is your talking about.

regards

desetfox

 

[PaulJackson]

ja500,

There appears to be some jargon (code words or phrases) in your description of the problem that someone may recognize and therefore be able to respond...

...BUT the deviations shown in qualify PASS the guage shown.

If these tolernaces are viewd in 'Insight then...

but for me your description is sort of muddy.

Are you using hard attribute gages?
Are you using software that simulates hard gages?
Are you comparing the results of hard and soft gage results?

One thing that I can tell you is that if you are using software to simulate hard gage results then there are often failure modes to the analysis routines that prevent erroneous results from propogating in the analysis i.e. when a datum feature size fails then its permissable contribution to "datum shift" will also fail.

As desertfox said, could you be more specific in describing the problem? What type of gages are you using? Can you describe or show the specification being measured?...

paul

 

[axym]

ja500,

For the benefit of those on the forum who are not coordinate metrologists, you need to explain the general situation and some of the terminology you're using.

By the sounds of it, you have some 3D point data collected with a laser tracker and you are analyzing it with different software packages. By "insight" I assume you mean the SMX/Faro Insight software that comes with the laser tracker. By "qualify" I assume you mean the Geomagic Qualify software, which is a post-processor that does soft gaging.

Your issue is that one or both of these software packages automatically fails any FCF that references a datum feature that fails one of its requirements? Is that correct?

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[ja500]

evan,

Yes my issue is that one or both of these software packages automatically fails any FCF that references a datum feature that fails one of its requirements MMC requirements. Is this what you would expect to happen?

 

[dingy2]

ja500:

Yes. If the datum feature fails a requirement then one does not have a datum and any FCF that references that datum also fails.

Dave D.

http://www.qmsi.ca

 

[MechNorth]

Yup.

Jim Sykes, P.Eng, GDTP-S
Profile Services

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com