interface control dwgs 2

[drdherl]

I would like to use interface control dwgs as a mechanism to ensure that an outsourced assembly meets form/fit (dimensional) expectations. Our drafting department is advising me that they do not believe interface control dwgs should have "real" dimensions and/or tolerances. They say that interface control dwgs should have only reference dimensions. I believe reference dimensions are "a dimension that is not crucial for the effective use of the part." . I believe an ICD should include only crucial information for the effective use of the part. As such, I believe an ICD should almost prohibit the use of reference dimensions, not the opposite.

Am I missing something? (Dftg group says dimensions and tols should be specified on lower level assembly dwgs and that ICDs should not be used as inspectable documents.). I myself feel lower level dimensions assembly dwgs should point to the ICD showing the lower level manufacturing source the end use requirement.

Please provide any guidance that you can provide.
Thanks...and have a grand day

 

[KENAT]

MM, while the OP never posted again to clarify, that wasn't their situation as I understood it.

If indeed by outsourced they mean the actual design not just fabrication is being undertaken then an interface drawing may be appropriate for the design stage but as I understand it still isn't intended for inspection. In this case I'd expect a control drawing of some type.

I agree with the OP's drafting group that interface drawings aren't intended for inspection.

I disagree with them about not putting toleranced dimensions on interface drawings when they are used, I like you believe that iaw the standard the critical ones should have tolerance or at least max/min where applicable.



KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:

http://eng-tips.com/market.cfm?

 

[drdherl]

I'm such a dope. I have read your replies many times and could not figure out how to re-post clarification. This AM, I looked again and voila...it is right there. Apologies...for my naivite'.

Here's the situation that (believe it or not), is still around.
I work in a large business. Aerospace. Our drafting department doesn't work for engrg dept. Drafting department says that ICDs should not have hard dims. They should have ref dims. Drafting dept will put reference tolerances too.
Their point is that they don't want ICDs to be used as inspection documents. They state that since dims/tols are shown on fab dwgs, they shouldn't be replicated and thus should be reference. I don't disagree with that mentality. (that said...If I were the user of the assembly, I'd want to make sure that the final assy i am buying meets requirements, not the lowest level)

Can someone clarify what is meant by :

Paragraph 1.4 of ASME Y14.5M-1994 states that "Dimensions and tolerances apply only at the drawing level where they are specified."

One can interpet this to mean that the feature and positional requirements of a hole pattern is no longer a requirement at the part's nha. Wouldn't this mean that for me to ensure that a critical feature is documented that that critical feature is respecified at the highest appropriate dwg level? (scenario is that holes get "boogered" up during assy process or mtg plate gets mounted to a warped surface all within the assemblies lower level dwg structure). For some reason, I thought requirements at lower levels flow up to highest level and didn't need to repeat. Above Y14.5 statement seems to contradict.


My problem with ref dims on ICD is that my perception is that an ICD needs to control key features.

The scenario being proposed is to put hard dims and tols on fab dwgs.
Replicate pertinant dims and tols from lower level fab dwgs on ICD
Put dims and tols as reference on ICD.

My issue is that if I am a user of an assembly, I sign the dwg of the ICD along with the owner of the assembly. I do not sign lower level dwgs. If for some reason the owner of the assembly does not maintain control of his assembly or inadvertantly changes his lower level parts and parts fall outside of the ICD range, which dwg takes precedent? I'd think that the dwg with hard dims would take precedent over dwg with ref dims. I suppose I could add a note that says in the event of conflict, ref dims and tols shown on ICD take precedence over hard dims/tols....which seems to contradict common sense.

drdherl

Y14.5 also states that ¶1.3.10 Dimension, Reference, "A dimension, usually without tolerance, used for informational purposes only.

Does anyone have an example of when one use reference tolerances?

 

[powerhound]

In my opinion, ICD's should only be for reference such as to show how an assembly is assembled. Engineering should do the work up front to ensure all parts will fit at assembly at both ends of the tolerance spectrum. If parts do not fit at assembly, it should be because something at a lower level did not meet print. If all parts meet print then one of the lower level prints is wrong. What would happen there if all parts met print but did not assemble correctly per the ICD?

Powerhound, GDTP T-0419
Production Manager
Inventor 2009
Mastercam X3
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[weavedreamer]

When using a modifier (M) or (L) referencing a feature defined on another print - you might include the dimension of the feature referenced as a reference.

 

[KENAT]

drdherl

What is your intended use for the Interface Control Drawings?

When I was in Aerospace we used ICD's as a way of controlling the interface between equipment with different Design Authorities. For instance, on weapons, the fuzing pocket and related features would have an Interface Control Drawing, this would allow different Authorities to design different fuzes that would all fit. These drawings were not used for inspection.

On the other hand, if you are buying in assemblies from a vendor and need to be able to do inspection then I'd suggest some kind of control drawing is more appropriate.

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:

http://eng-tips.com/market.cfm?

What is Engineering anyway: faq1088-1484

 

[drawoh]

drdherl,

What exactly is being outsourced?

When your vendor submits whatever it is they do for you, you have to inspect it to verify they met your requirements. If you need to control dimensions and tolerances, you need a drawing done to ASME Y14.5M-1994, or its ISO or JIS equivalent. The vendor may have generated fabrication drawings, but if you cannot get at them, or you are unwilling to take the device apart to inspect the individual components, they are irrelevant. They might as well not exist. You need an inspection document. Perhaps you can call it a specification control!

It sounds like your drafting department is rule driven, following procedures, rather than trying to get work done.

JHG

 

[drdherl]

I'm sorry...the term outsourced might be misleading. I work in a large company with lots of independant departments. I am in department B. If I am using assemblies from departments A, C, D I am not formally authorized to tell them how to do their job correctly. Mgmt and QA have been too busy/distracted to deal with the issue. I have situations where I have their fab dwgs and their ICD and they do not match (in violation of) ICDs. Since ICDs are not to be used for inspection, their fab dwgs take precedence and any subtle disconnects are put in a big pile of unquantified risk, assumed by the user (me). I'm trying to get to a sitaution where I hold the separate departments (i.e. outsourced) accountable to ensure that they supply parts that meet ICDs. If they don't care to spend the time to make sure their parts are built to the ICD, that's their problem. If I can get to a situation where my requirements database says "widget shall conform to ICD # xxx", I might have better leverage to reduce the pile of unquantified fit risk. Specifying dims and tols as reference on the dwg that I sign reduces my leverage. (I don't sign their fab dwgs or change notices)

 

[KENAT]

So it sounds like you truly do need an Interface Drawing then and that the discussion of inspection was a bit off tangent.

I would say that it most definitely can and should have tolerances per ASME Y14.24-1999 Section 9. While we can't over rely on figures, Fig 21 which is a sample Interface Drawing does show toleranced dimensions. 9.3(a) says "cinfiguration and interface dimensional data applicable to the envelope, mounting, and interconnection of the related items;" While it doesn't explicitly say 'tolerancing' I believe this is implicit, and as mentioned the example definitely gives tolerances.

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:

http://eng-tips.com/market.cfm?

What is Engineering anyway: faq1088-1484

 

[drawoh]

drdherl,

There is yet another issue here.

As any organization gets larger, the left hand ceases to know what the right hand is doing. As it continues to grow, the right thumb ceases to know what the right index finger is doing, and so on. If your companie's engineering and drafting department comprised you and your best buddy, sitting at the next desk, you can get away with sloppy communications and procedure. As your company grows, you have to become methodical. There is a certain amount of overhead required for you and your co-workers to stay organized and correct.

If you have no say in how departments[ ]A and[ ]C do their work, you should not be handling their fabrication drawings. They should be providing you with the information you need to design your stuff. Definitely, this includes dimensions and tolerances. Definitely, this document should be kept accurate.

This may be a terminology problem. Stop calling the thing an ICD. I put critical enginering information on arrangement drawings. Make up terminology. Call it an Interface Reference. Name it after somebody's cat.

JHG