General Profile Tolerance on Basic Dims -- CMM Inspection

[DannoTheManno]

I've got a customer print with true position on holes, and basic dimensions locating said holes. There is also a general note "Unless otherwise specified, all features located using basic dimensions shall be [<profile> .020|A|B|C]." Per the print, ANSI Y14.5M - 1982 applies.

Can I assume the general profile tolerance does not invoke the inclusion of these basic dimensions on the FAIR? I am assuming NO. Size, perpendicularity and true position dimensions are reported on the FAI.

When CMM inspecting these (for internal verification only between 5-axis machining steps), we are currently inspecting to the tighter title block tolerance of +/-.01 for .XX dims and +/-.005 for .XXX dims. We are consistently meeting the title block tolerances for all basic dims.

Are we safe inspecting to the tighter title block tolerances? Should we be generating the profile and inspecting as such with the CMM?

Thank you.

DJ

 

[Burunduk]

The basic dimensions shouldn't be on the FAI report, except as auxiliary information, but the more practical approach is to report surface deviations with plus or minus signs.

The measured value for the profile tolerance must be in the report.

 

[greenimi]

Y14.45 (the reporting standard) is very clear about reporting basic dimensions and has an entire chapter about that "Reasons characteristic identifiers shall not be applied to basic dimensions"

 

[greenimi]

Are we safe inspecting to the tighter title block tolerances? Should we be generating the profile and inspecting as such with the CMM?

This question about "safety" needs a little more clarification.
Are you talking about basic dimensions that are related with the general profile or you are talking about some dimensions which do not have any tolerances (and consequently use the title block tolerances)?

 

[DannoTheManno]

Basic dimensions which use the title block tolerance. We are inspecting the basic dimensions to title block tolerances, but we are not reporting. We also inspect those dims/features for profile per the profile note. Only thing that will be reported (in regards to those basic dims) is the profile results.

 

[jassco]

Hi, DJ:

You are not supposed to inspect the basic dimensions to title block tolerances as they are not specifications.

Best regards,

Alex

 

[greenimi]

Basic dimensions which use the title block tolerance. We are inspecting the basic dimensions to title block tolerances, but we are not reporting. We also inspect those dims/features for profile per the profile note. Only thing that will be reported (in regards to those basic dims) is the profile results.

Okay, I understood about reporting, but I am asking what about if there is a conflict between those ?
So, what about if the feature is acceptable per the "basic -title block" combo and it is rejectable per the general profile? What are you gonna do with the parts?

Also, on the other way around: if the part is rejectable per the "basic-title block" idea and it is acceptable per the general profile (tolerance zone approach)?

Which one takes precedence?

 

[Burunduk]

Danno,
The +/- title block tolerances apply only to implied right angles not otherwise controlled by geometric tolerances such as perpendicularity, or untoleranced dimensions not indicated as basic by a frame or a general note.

If you are measuring the basic dimensions for process control and adjustment purposes, consider recording surface deviations instead. These can be generated by the CMM during the profile inspection anyway, and are more direct in telling the dimensional error that should be corrected in case of nonconformance. It eliminates the need to calculate the difference between the measured and basic dimensions, and can be very specific as to where the worst deviation is, in terms of coordinates relative to the inspection axis system.

 

[jassco]

Hi, greenimi:

If there is a conflict, then there is something wrong with the print. A good print should have only one interpretation.

Best regards,

Alex

 

[greenimi]

If there is a conflict, then there is something wrong with the print.

The print might be good "as -is", but people are not reading it according to the rules and regulations specified in the applicable standard.
It is a matter of education, I guess.
_{"A friend once told me that an education is like an erection — when you have one, it’s obvious"}