Major Dia callout for position of threaded hole 1

[SpaciouS]

Is "MAJOR DIA" placed under a position FCF, for threaded holes, something that should be done? Initially I was taught to do this from my first GD&T mentor. But I do not regularly see this and I can't find documentation to support this.

Thanks,
Sean

 

[fsincox]

It is supposed to be determined by applicational requirements not just a desire for an ease of inspectablity. However compromises are very common in practice.
Frank

 

[dingy2]

Sean:

On a threaded stud, it may be appropriate to place "MAJOR DIA" under the positional feature control frame otherwise the positional tolerance would default to its pitch diameter.

In the above situation, one may create a checking fixture to confirm the position of the studs at its largest diameter while using a pitch diameter, one would need an additional operation of threading a checking plug onto each of the studs. The checking fixture would then apply to the plug diameter rather than the threaded stud.

Dave D.

http://www.qmsi.ca

 

[SpaciouS]

Sorry I completely meant to state "MINOR DIA"

Thanks,
Sean

 

[SpaciouS]

Dave, the statement you made, 'otherwise the positional tolerance would default to its pitch diameter' is what I understand it to mean as well. That being said, if I callout positional tolerance at MMC and add 'MINOR DIA' under the FCF, the inspection gage could simply be a pattern (if more than 1 FOS) of fixed plugs right? And the threads are inspected separately with a pitch gage?

The reason I ask is the only way can picture pitch being inspected with position is with a pattern (if more than 1 FOS) of pitch gages that are simultaneously threads, is that correct?

Thanks,
Sean

 

[dingy2]

Sean:

MINOR DIA is used on a threaded hole while MAJOR DIA is used on a threaded pin. Placing MINOR or MAJOR in the wrong situation would really cause havoc.


Dave D.

http://www.qmsi.ca

 

[SpaciouS]

Dave & Frank, thanks.

Does anyone know of where this topic is documented?

Thanks,
Sean

 

[fsincox]

In ASME Y14.5-1994 it is section "2.9 SCREW THREADS"

 

[KENAT]

Specifying 'minor' arguably can simplify inspection for threaded holes, but is at the expense of 'using up' some tolerance (or however you like to term it).

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