Profile With Respect to an Axes

[OmarEn07]

Hello Guys,
I have a question about a drawing sent by Ford to the Fluids Division of my company.
In this drawing, there is a datum target call out at pitch dia of the nut (A1).

The intent is to control the Line to not be either larger not shorter than 3.0mm with respect to its basic/nominal location.
But I think the way the customer is calling it out is wrong, because the profile tolerance is only with respect to A.
As it is now, actually means that the end surface could be larger or longer than 3.0mm as long as it is perpendicular to datum A (center axes).

I think the correct way would be to add to the FCF secondary and tertiary datum features to actually be able to locate and orient that end surface in space, and not only its orientation.

What do you guys think about it?

Thanks in advance for your time,
Regards.

Omar Rios
Quality Engineer and Gage Specialist
GDTP-T
Martinrea Arteaga México

 

[3DDave]

That's target A7, so there are at least 6 more targets in A. I don't know how one applies an MMC/MMB modifier to targets, so there's that.

 

[Belanger]

3DDave, FYI -- the Y14.5 standard says that "Where targets are applied to a feature of size, the appropriate material boundary modifier is specified or implied." (end of paragraph 4.24)
I guess that doesn't answer your question about "how" but at least it's legal.

For this application, yes we'd have to see the other "A" targets. If they act in a direction different from A7 then the profile tolerance to A{M) might be OK.


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

 

[3DDave]

Targets. Not a target, but good on the reminder; it seems unlikely that all the targets will be FOS. Plus it looks like they are going out of their way to force the user of the drawing to pull the specification of the fitting to see what the range of the acceptable pitch diameter is, so there is a certain rudeness to the process.

 

[OmarEn07]

Hi Guys,
Thanks for your answers.
I am attaching the whole drawing here. indeed, there is more than one datum target and they are in different directions.
plus, some of them are called out to a Feature of size... is this legal per Y14.5? If so, I guess the pin/hole in the Gage would be the size indicated in the upper half of the datum target symbol, but if it has a size tolerance when that component is at MMC, it could not fit into the gage pin/hole. Additionally, I am not sure if the MMB is referring to all features of size A1 - A7 are allowed to shift.

Thanks again for your help.
Regards.


Omar R.
Quality Engineer and Gage Specialist
GDTP-T

 

[greenimi]

For me the design intent is somewhat clear: the end surface is a sealing surface and must be oriented/perpendicular within 6mm to the axis drivedn fron the pitch diameter cylinder. Location of the sealing surface (again, not orientation) is probrably, as 3D Dave said, defined in the fitting specification.
Not sure if the SEP REQT is appropriate for those profile callouts, as we do not want simultaneous requirement to be enforced.
The datum feature shift is comming from the thread and per other (multiple) discussion we had here is not very significant on a straight thread and MMC/MMB is the correct callout for the straight threads, but would be RFS/RMB if this thread is NPT/conical.

I am sure would be people to disagree with me and I am perfectly fine with it.

 

[greenimi]

Also the general note states that unless otherwise specified , at terminations of all tube ends should be within 6 to A(M) primary and B secondary. I would say here it is the location control. Again, the orientation control is the one shown on the drawing (profile within 6 to A(m) primary. Again, if I am wrong to decode this drawing (and its GDT) I will stand corrected.

Please, do not ask why the profile shown on the print does not overite the unless otherwise specified on the note and I am treating it as a refinament.

 

[MintJulep]

I'd guess that your company signed an agreement with Ford saying that you will keep drawings confidential.

Posting a complete Ford drawing on the internet probably violates that agreement.

 

[3DDave]

I'd suggest red-flagging that drawing post - not a good idea to wave the customer laundry.

 

[3DDave]

Also, there is no chance that a 6mm deviation in orientation is possibly acceptable in the final product. That would put a tremendous load on the tubing at installation to make up for it. This looks more like a drawing that says "make this part so it fits right on the assembly line" and here's some stuff to make the requirements look good. A real effort at a drawing for a part like this would indicate that there is a limit to the amount of force required to push the part mounting provisions to the exact locations shown and an overall tolerance for the volume the tubing can occupy in between the places it will be attached to the chassis when it is forced to those locations. I expect the tolerance values given are far in excess of the variation the tubing bender is capable of so that the QC charts look really good. Win-win.

Note that the general method shown on the drawing (excepting using all those datum 'targets') is typical for tubing, but it is also both lazy and time consuming - basically lazy for not setting the tolerance based on the stress analysis/how easy to install and time consuming for putting a bunch of requirements on a drawing that are excessively limiting in some areas and insufficient to do the job in others. See MIL-D-9898 (currently inactive for new design, but no replacement suggested.

http://quicksearch.dla.mil/qsDocDetails.aspx?ident_number=7794)

for the older style - LRA format which is more suitable for hand bending. I do like this document and the frustration expressed in dealing with tubing inspection:

https://www.clarkfixtures.com/wp-content/uploads/2012/06/whitepaper.pdf

It includes suggestions for approaches to the problem.

 

[greenimi]

3DDave,
So, looks like you have no objections to my print interpretation? (except the 6mm tolerance is way too big, but that's coming from the print).
How would you ready the GD&T callout, as shown?

 

[3DDave]

The sealing surfaces are the flared ends of the tube, the nuts are a clearance fit so they will tend to rattle and not make a good datum feature. There are probably a ton of other requirements in related documents so interpretation is presently left to the imagination of those without them.

 

[OmarEn07]

The design intent of this drawing is to say that end surfaces have 6.0mm profile tolerance (+/- 3.0mm).

But the way the designer is trying to convey it is a bit weird. calling out datum targets, these being in several directions, and being features of size... At least I have not seen this done before.



Plus, calling out datum targets at its MMB that way is something that I could not support in the standard.

Omar R.
Quality Engineer and Gage Specialist
GDTP-T

 

[greenimi]

Omar,
I guess datum targets at MMB is legal and supported by the standard. And A(M) is recommended for straight threads.
I would use the word INDIVIDUALLY if separate requirements is not something feasible and acceptable for the design intent.
Still not sure if the shown profile will control location or orientation only.
For location a basic dimension is needed. I assume this required basic dimension could be found from the fitting specification.

 

[TheTick]

Auto makers get away with lots of stupid stuff on their drawings because they’re big and no one has the guts to argue with them. Often the stupidity takes on a life of its own, growing from cut-paste to accepted practice to dogma.

 

[chez311]

So this thread (and 3DDave your post in the other thread regarding treating FOS as a datum target) has me wondering - per the wording in 4.24 "Where targets are applied to a feature of size, the appropriate material boundary modifier is specified or implied" use of MMB with a datum target is perhaps legal (with the caveat that 3DDave pointed out the standard is plural probably referring to multiple targets not a single target), but what exactly would that look like? As in, what would the datum feature simulator look like in the OP's example? Or to simplify it, what would the simulator be if a single datum target was applied to a regular FOS - say just a simple hole? This doesn't seem right to me to use datum targets in this manner...

 

[3DDave]

It would have been cleaner if the standard referred only to points and lines as targets and all areas as limited datum features. The use of a chain line can indicate a limited portion of a feature but no one calls that a target chain. I guess we are stuck with the errors of the past, which tend to accumulate.

Specifically I was wondering how a bunch of individual surfaces in a variety of orientations could collectively have a material boundary, especially when the drawing gives no clues at all what those boundary limitations could be. The use of plural in the standard is just a phrase, and an unfortunate one, but those writing these rules are privy to conversations in which specific wording makes sense. Without those supporting conversations the wording is ambiguous.

 

[chez311]

3DDave,

The plural I figured referred to something similar to 4-53 where B1-3 are all on the same feature (170 OD) and might interact with that OD depending on the material condition. I am with you as to being mystified how a collection of individual datum targets on separate surfaces and FOS could collectively produce a material boundary. I think thats probably a bit of a stretch.

What I am really curious about is if a single datum target is applied to an entire FOS as it is here, what would that look like? Is that even allowed?

It would have been cleaner if the standard referred only to points and lines as targets and all areas as limited datum features. The use of a chain line can indicate a limited portion of a feature but no one calls that a target chain. I guess we are stuck with the errors of the past, which tend to accumulate.

Could you expand on this? What do you mean in regards to applying a single datum target/area to an entire FOS?

 

[chez311]

I guess I've answered my own question after a little bit more reading - described in 4.24.11 and shown in figure 4-52 circular target lines and target areas are utilized on a non-planar (round) surface to apply a single datum target to a FOS.