【转帖】interface control dwgs

yang686526

interface control dwgs
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

drdherl,
   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".
               jhg
welcome to a world of confusion.  (i'm going to assume you work to asme standards, if not state what you work to).
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?
kenat,
one note, if there are any dimensions which are 'set' at the top assy level, then obviously these should be listed there.  however, something like a hole pattern in an individual compononet should probably be captured at the piece part level (unless machined at the assy level).
kenat,
normally i have seen icds with toleranced dims and gd&t.  the icd is communicating feature locations for proper fit and function of other mechanical systems.  i have never seen one with reference dims, except perhaps for overall lengths and height.
"art without engineering is dreaming; engineering without art is calculating."
as usual, i agree with kenat...
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."fff"> - george bush, washington dc, 27 october, 2003

i can't argue with mango; the installation drawings that i have seen do show toleranced dimensions with gd&t.  i just can't find the justification for this in the standards, thus my advice on using reference toleranced dimensions. i have yet to see referenced gd&t on a drawing (but haven't read anything prohibiting it, either).
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."fff"> - george bush, washington dc, 27 october, 2003

ewh, y14.24 clearly shows tolerances in the example control drawing.  sadly it doesn't explicitly state that repeating tolerances given elsewhere in the pack is ok or similar.
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.
  
kenat,
if the parts become "inseperable assemblies" welded, pressed, glued, riveted, heat-treated etc. "altering the sub-component features" so that they cannot be individually scrutinized as originally produced... then they are a new part that must be fully dimensioned.
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   
check out 4.8:
from chris's link "it is not to be used to manufacture parts." which is one of the points i was trying to make about how the op wanted to use the interface drawing.
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.
kenat,