What is the proper way to apply GD&T to a box thread with an internal sealing surface?

[CADCAMTech]

I apologize if this is a repeat thread but I could not find the answer I was looking for. In the file I attached is there a proper method to apply a geometric dimension based on the Face Square To Thread note. I would like the shoulder to be perpendicular to the thread so that when the corresponding part is threaded into this coupling a face seal is achieved. Thanks in advance for any help you can give me.

 

[djhurayt]

make the axis of the threads a datum, and then add a perp to datum callout on the 1.44 face

???

 

[CADCAMTech]

I had thought of that too but I am not to sure how to verify that during inspection.

 

[CADCAMTech]

Would I apply the datum identifier to the OD of the part since that is how it is most likely to be held during inspection? Then I could say that the 2.1093 dim is co-axial with the datum identifier, and the 1.44 dim is perpendicular to the datum identifier?

 

[ewh]

Identify the flat face as your primary datum, the OD as the secondary datum and control thread position to those (which would control the thread perpendicularity to the face).

"Know the rules well, so you can break them effectively."
-Dalai Lama XIV

 

[drawoh]

make the axis of the threads a datum, and then add a perp to datum callout on the 1.44 face

Do not apply datums to axes. I count six features, any one of which could define the centre axis. The thread has a minor, pitch and major diameter. EWH's suggestion sounds good to me.

--
JHG

 

[djhurayt]

drawoh,
It may be a matter of semantics, but isn’t attaching a datum symbol to any one of the three thread pitch diameters simply making the axis of that feature a datum? Just asking.

And to clarify, although I did not say it as you did, I did not mean to attach the symbol to the axis on the drawing because as you said there are multiple features that could be used to get this "axis".

 

[drawoh]

djhurayt,

Attaching a datum to one of the thread diameters makes the centre axis of the thread your reference geometry. Ask yourself how somebody is going pick this feature up. I try very hard to not use threads as datums.

You are assuming that the other diameters are centred perfectly on the thread. I would not assume that. Will the thread minor diameter be centred perfectly on the pitch diameter and the major diameter?

--
JHG

 

[djhurayt]

Got it. Your comment appears to habe been with regard to the ability to find the "axis" of the threads, and yes I agree dificult at best. As EWH suggested, using the OD as a datum, which is much more locate-able still uses an axis as a datum just not the axis of the thread component diameters.

FYI: my interepration of your initial reply "Do not apply datums to axis" seemed contraditory to what attaching a datum flag to a diameter dimension indicates, doesn't it?

 

[CheckerHater]

Manu,

If you say "FACE SQUARE TO THREAD" then thread is your datum and face is your controlled feature.

In your comment you say " had thought of that too but I am not to sure how to verify that during inspection."

So, how YOU think the requirement will be verified during inspection? Also, exactly how square?

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

 

[CADCAMTech]

The "face square to thread note" is off of an old drawing but we are outsourcing this part to another shop and they have asked for geometric tolerancing on this part. I cannot find anywhere in the API standards we use that actually specifies how square that face should be. I just know that it is a sealing face. When we make this part in house the face square to threads note is more than adequate for us to manufacture the part. I am not even totally sure if QC even checks it. I am trying to give the company doing the machining without over specifying the part and having them spend a bunch of extra time making and QCing the part.

 

[ewh]

I know that it may just be semantics, but a centerline is never a datum. The centerline would be the axis of a datum.
The OD of your part can be a datum and it's centerline would then be the axis of that datum.
See Y14.5-2009 paragraph 4.8.2 for clarification. It states in part "The datum feature symbol identifies physical
features and shall not be applied to center lines, center planes, or axes."

"Know the rules well, so you can break them effectively."
-Dalai Lama XIV

 

[Belanger]

ewh -- you should re-read the definition for a datum. It's actually the opposite of what you are stating! The OD of a part is NOT a datum. (It's a datum feature.)
A datum is a theoretically perfect axis (or plane, line, point, or combination of these).

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[ewh]

Got me! I actually had that typed, then went to editing and "feature" got lost somehow...
I still stand by what I had meant to convey... a centerline is not a datum, but can be a datum axis derived from a datum feature.

"Know the rules well, so you can break them effectively."
-Dalai Lama XIV

 

[Belanger]

No prob

It may be better to say that a center line should never be labeled as a datum. (A center line can indeed be a datum, but I see that you were referring to the "datum feature symbol.")

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[powerhound]

Is this a box/pin interface for a drill pipe?

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech
SSG, U.S. Army
Taji, Iraq OIF II

 

[CADCAMTech]

Powerhound no this is not for drill pipe its a pump barrel connection. Thanks every one for all your help. I have done as ewh suggested further up and made the face datum feature A and the OD datum feature B, I have also attached an image. I am just not sure if I need the Perpendicular tolerance as well as the positional tolerance, or if just using the positional tolerance and then referencing both datum feature A and datum feature B is acceptable.

 

[djhurayt]

I think (???) you need a diameter symbol in front of the tolerance magnitude.

Otherwise, I think (???) you are specifiying a square tolerance zone.

???

 

[CADCAMTech]

Yes I do djhurayt, I missed that thanks.