Digging Datums - Feature control frame (FCF) applied to a pipe I.D.

optomist1

A Sea of Statistics
Trusted Information Resource
#1
Hi To All,
Searched but unable to find an answer, don't have drawing to post but here's the question. Given a cylindrical pipe with a mounting flange and a feature control frame (FCF) applied to the pipe I.D. , requiring a tolerance of position of 0.05(cylindrical tolerance zone), with Datum A (the pipe flange planar, normal to the pipe length) referenced and Datum B referenced. The problem, this FCS sets up or establishes Datum B an axis......a FCF that establishes a Datum and references the same datum.....is this acceptable?
Thanks,
Marty
 
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Stijloor

Staff member
Super Moderator
#2
Re: Digging Datums

Hi To All,
Searched but unable to find an answer, don't have drawing to post but here's the question. Given a cylindrical pipe with a mounting flange and a feature control frame (FCF) applied to the pipe I.D. , requiring a tolerance of position of 0.05(cylindrical tolerance zone), with Datum A (the pipe flange planar, normal to the pipe length) referenced and Datum B referenced. The problem, this FCS sets up or establishes Datum B an axis......a FCF that establishes a Datum and references the same datum.....is this acceptable?
Thanks,
Marty
What are the primary and secondary datum features?

Stijloor.
 
Last edited:

optomist1

A Sea of Statistics
Trusted Information Resource
#3
Hi Stijloor,

Primary Datum Feature A is the pipe mounting flange which is perpendicular or normal to the length of the pipe (there is a flatness control applied to this planar surface/datum), Secondary Datum Feature B is the I.D./FOS of the thin walled pipe.......

Thank you...

Marty
 

Stijloor

Staff member
Super Moderator
#4
Hi Stijloor,

Primary Datum Feature A is the pipe mounting flange which is perpendicular or normal to the length of the pipe (there is a flatness control applied to this planar surface/datum), Secondary Datum Feature B is the I.D./FOS of the thin walled pipe.......

Thank you...

Marty
Marty,

I made a sketch using the information provided in your two posts (1 & 3).

The positional callout you described is incorrect because the secondary datum feature (of size) which is used to develop datum (axis) "B" is also the controlled feature. Does this appear on an actual drawing? :mg:

Now, if the design intent is to have the axis of the ID of the pipe perpendicular with the flange, then the position symbol must be replaced with the perpendicularity symbol.

The Feature Control Frame should then read: Perp at (dia) 0.05 to Datum A.

Just a few thoughts. Hope this helps.

Stijloor.
 

optomist1

A Sea of Statistics
Trusted Information Resource
#5
Marty,

I made a sketch using the information provided in your two posts (1 & 3).

The positional callout you described is incorrect because the secondary datum feature (of size) which is used to develop datum (axis) "B" is also the controlled feature. Does this appear on an actual drawing? :mg:

Now, if the design intent is to have the axis of the ID of the pipe perpendicular with the flange, then the position symbol must be replaced with the perpendicularity symbol.

The Feature Control Frame should then read: Perp at (dia) 0.05 to Datum A.

Just a few thoughts. Hope this helps.

Stijloor.
Hi Stijloor,

yes, once again seeking "Stuart Smalley" affirmation....hopefully stating this correctly; one cannot use a FCF to among other things establish a Datum and reference the same Datum in the Datum portion of the same FCF. This is on a drawing that was used for quiz purposes so this GD&T trangression may have been part of the question.

Thanks again,
Marty
 
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