interface control dwgs
interface control dwgs
(OP)
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
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





RE: interface control dwgs
If you are ordering something from a vendor and you need to control dimensions, then you need proper dimensions and tolerances on the drawing. There is no difference between this, and a regular fabrication drawing.
Perhaps you need terminology other than "interface control".
RE: interface control dwgs
If I get this straight, you have assemblies for which you fully control the design/drawing pack is yours but which are being manufactured externally?
If this is so then your drafting group is probably correct in so much as the dimension/tolerance should probably be captured on the lower level part or assy drawing ASME Y14.5M-1994 1.4(n) is possibly relevant here. " Dimensions and tolerances apply only at the drawing level where they are specified."
An Interface Drawing is more about controlling interfaces between items/systems from a design change point of view. See ASME Y14.24-1999.
You are however correct that Interface Drawings when used probably should normally have tolerances on dimensions, at least on the key interfaces they are controlling (it's a different matter if a some overall ref dimensions or something are added just to help get an impression on how big the part is or something). Certainly the example in 14.24 shows tolerances, or a lot of min/max dimensions. In practice though a lot of interface drawings I've seen don't have tolerances, at least not meaningfull ones.
There is nothing to stop your quality/incoming inspection or whoever you were going to prepare the Interface Drawings for from having a marked up copy of the assy that they transpose the relevant dimensions to from the lower level drawings and use as an aid in inspection. However, I'd expect this to form part of the quality plan or similar not be a formal drawing that's part of the pack. Also you need to worry about keeping this up to date.
Now, if you're outsourcing the design of the assy then you should be looking at a Control Drawing, possibly a source control drawing.
Any help?
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RE: interface control dwgs
KENAT,
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RE: interface control dwgs
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RE: interface control dwgs
Per Global "Drawing Requirements Manual":
"An interface control drawing shows physical and functional interface engineering requirements of an item which affect the design or operation of co-functioning items. These drawings are used as design control documents, delineating interface engineering data coordinated for the purpose of: (a) establishing and maintaining compatibility between co-functioning items; (b) controlling interface designs thereby preventing changes to items requirements which would affect compatibility with co-functioning subsystems; (c) communicating design decisions and changes to participating activities."
Per ASME Y14.5-1994:
¶1.3.10 Dimension, Reference, "A dimension, usually without tolerance, used for informational purposes only.(italics mine)
¶1.4(n) "Dimensions and tolerances apply only at the drawing level where they are specified."
Your drafting group is correct regarding repeating dimensions; however there is nothing in the standards that I have seen which prohibit the use of reference toleranced dimensions, and this would be one way to include the required information on the interface drawings.
Include the necessary detail drawings denoting the required dimensions with the interface drawing.
"The ambassador and the general were briefing me on the - the vast majority of Iraqis want to live in a peaceful, free world. And we will find these people and we will bring them to justice." - George Bush, Washington DC, 27 October, 2003
RE: interface control dwgs
"The ambassador and the general were briefing me on the - the vast majority of Iraqis want to live in a peaceful, free world. And we will find these people and we will bring them to justice." - George Bush, Washington DC, 27 October, 2003
RE: interface control dwgs
However it does say 9.3 (
a) "configuration and interface dimensional data applicable to the envelope, mounting, and interconnection of the related items;
(c) any other characteristics which cannot be changed without affecting system interfaces.
So I'd say having tolerances is correct but, in some cases just giving the max or min value rather than the actual tolerance may be appropriate.
That said, I think it's the reason the OP states for having an Interface Drawing/their intended application that takes it outside of the intended scope of such drawings.
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RE: interface control dwgs
This fact is vigorously resisted by manufacturing because functional feature confirmations verified up-stream "they say" should not be "rechecked" down-stream.
The problem is that the customer, the assembler, and the stockholder ultimately has to live and/or die with unpredicted variation.
My advice when tolerancing "inseperable assemblies" for economy's sake... re-specify the stuff that you predict will make it work or fail. It is not dual dimensioning... it is a new part!!!
Paul
RE: interface control dwgs
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RE: interface control dwgs
Arguably, if you aren't manufacturing to it then I wouldn't think you should inspect to it, which it sounds like the OP wants to do.
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RE: interface control dwgs
This is true, and I have seen the example. I just get stuck by the Y14.5-1994 ¶1.1.4 discalimer that figures are intended only as illustrations...
Does Y14.24 have a similar statement (I don't have the standard handy)?
"The ambassador and the general were briefing me on the - the vast majority of Iraqis want to live in a peaceful, free world. And we will find these people and we will bring them to justice." - George Bush, Washington DC, 27 October, 2003
RE: interface control dwgs
¶ 1.5 states "Sample drawings and other illustrations are included as needed to illustrate the text and the characteristics unique to a particular drawing type... The content and arrangement of sample drawing types are for illustration only."
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RE: interface control dwgs
However, I think a & c implicitly OK giving tolerances or at least min/max where applicable.
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RE: interface control dwgs
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RE: interface control dwgs
It would probably be best if interface drawings were not considered to be in the same group as part/assembly definition drawings, because by their nature dimensional data is required for them to be of much use.
Now, if only such a statement were in the standards.
"The ambassador and the general were briefing me on the - the vast majority of Iraqis want to live in a peaceful, free world. And we will find these people and we will bring them to justice." - George Bush, Washington DC, 27 October, 2003
RE: interface control dwgs
Some of the dimensions in Fig 21 are toleranced, not all are just max or min, look at the bottom view sh2 where most of the dimensions are toleracned.
But basically I agree with MM, and while it might be nice I'm not sure the standard needs to explicitly state it. I think a & c inherantly OK it.
But we're maybe getting caught up in symantics and straying away from the OP question.
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RE: interface control dwgs
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RE: interface control dwgs
Hence whether it has toleranced or referenced dimensions is almost irrelevant.
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RE: interface control dwgs
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RE: interface control dwgs
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.
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RE: interface control dwgs
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(n) 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?
RE: interface control dwgs
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RE: interface control dwgs
RE: interface control dwgs
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.
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RE: interface control dwgs
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.
RE: interface control dwgs
RE: interface control dwgs
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.
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RE: interface control dwgs
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.