Positional tolerance with annotation

[ak762]

What is your opinion I am confused a little. Fastener holes specified with positional tolerance annotated Minor diameter.
I would understood if it will be specified for screw thread typically for drive screw but not for fastener hole.
Perhaps someone direct me to reference doc where it is clarified.

 

[SeasonLee]

The rules for screw threads---Unless otherwise specified, all geometric tolerances and datum references apply to the pitch diameter, this is default but an exception to this practice is necessary, MAJOR DIA or MINOR DIA can be stated under the FCF.You may find them from 2009 standard on section 2.9 page 31 and Fig. 7-35, while the 1994 standard is on section 2.9 page 29 and Fig. 5-62.

Normally, MAJOR DIA or MINOR DIA is an easy way to check and the data you measured is rough not precise.

SeasonLee

 

[KENAT]

To follow what SeasonLee says...

One reason you might choose 'minor' rather than pitch dia on threaded hole patterns is it can simplify inspection - specifically use of gauges.

Same goes for 'major' on male features.

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[ak762]

I doubt that such annotation can help to simplify inspection. Gauges will support to irregular surface instead inclined walls thread's profile.
Burr can be present at profile tips because thread cut is final operation. If position tolerance is critical for fit fastener then better to specify it with project zone or add additional round surface for male and female fastener features. Generally bolt can be used as gauge even if we speak about simplify.
My opinion it is incorrect to specify such annotation and I would reject such drawing. May be someone share other arguments?

 

[SeasonLee]

Projected tolerance zone is another concept on the threaded parts, normally this is recommended where the perpendicularity of the threaded hole (female part) is important, it will prevent the interference with mating parts.

Of course, there are other factors will cause interference on your assembly, straightness error of the fastener body is one factor, thread to shank runout of the fastener is the other factor will affect assembly.

SeasonLee

 

[KENAT]

ak762, specifying minor or major, to allow use of quicker inspection gages/fixtures is not uncommon.

Yes there is a hit on accuracy (or is that precision or something) that has to be taken into account with how the position tolerance is specified and the gage made, but it is used.

In fact I was introduced to the concept by a former 14.5 committee member.

I've made use of it, on a piece with a large threaded hole pattern we wanted a gauge to give a quick check if the part was good. It was accepted that some precision would be lost but given that CMM of the part was out due to size limitations & the need to keep it 'clean', it gives a 90% solution.

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[KENAT]

Section 2.9 of ASME Y14.5M-1994 mentions use of MAJOR & MINOR.

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[dtmbiz]

It may be your opinion that adding major dia or minor dia to a TOP FCF for threads is incorrect. It may not satisfy a particular requirement for a certain senario. However it is not an "incorrect" callout per ASME Y14.5M 1994. Page references are noted in previous posts.