Tolerance block on customer drawing - Major interpretation problem with customer

D

Dave Dunn

#11
Re: Major interpretation problem w/ customer

Assuming that I am understanding the situation correctly, the feature is marked only with .460 min, and the tolerance that you've referred to is what is in the drawing title block as a general tolerance (UOS). My interpretation is that the drawing would permit the feature to be no less than .460, but have no maximum.

What standard (if any) was the drawing created under? ASME Y14.5M?
 
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QMMike

Involved In Discussions
#12
Re: Major interpretation problem w/ customer

Assuming that I am understanding the situation correctly, the feature is marked only with .460 min, and the tolerance that you've referred to is what is in the drawing title block as a general tolerance (UOS). My interpretation is that the drawing would permit the feature to be no less than .460, but have no maximum.

What standard (if any) was the drawing created under? ASME Y14.5M?
That is how I saw it. Tooling was actually cut to .480 (it's an extrusion).... Samples were submitted originally in 2002 and passed. Customer does not abide by any standard for creating drawings...
 

Brizilla

Quite Involved in Discussions
#13
Re: Major interpretation problem w/ customer

Yep. The horse [Contract Review was missing] is dead - we can stop beating it.

FYI:
Typically, my experience with job shops and contract manufacturers is that they do not take an ambiguous note or dimension as carte blanche approval to FAR EXCEED the standard tolerances for the drawing. Thus said, I would have expected most shops to have interpreted the dimension (assuming no other customer interaction during Contract Review) as 0.460 +0.020/-0.000. This means the maximum part sent to the customer would have been 0.480.
True, but as a job shop and contract manufacturer most of those dims are taken AS IS and treated as a reference dimension. The Min does supercede the tolerance block, the .460 min. is honored but the actual dim needs only to be close. (Close being relative to the size of the part, it's other toleranced dimensions, the caveat in the tolerance block, history with the customer and other variables.) Usually when a dimension like this considered critical by a customer it's because it is stacked against other dimensions WITH tolerances that will keep the critical dimension in control on their own. Obviously, in this instance that was not the case. Every shop has their own standard tolerance for customers that fail to provide tolerance blocks (believe it or not a standard problem on customer prints) but in this case the .460 min. is definitive. Plus, samples were already submitted and passed 5 years ago. One question though, what did those dims measure at in that inspection?
Unfortunately, that may still not save them, being right and the customer being happy don't necessarily fall under the same tree. I agree with Jim Wynne
"This is a matter of negotiation with the customer, and in order to avoid complications you might well end up having to eat the "nonconforming" parts. This doesn't mean that the customer shouldn't be put on notice that you are making a concession in order to maintain their happiness, and that the drawing (and any others like it) need to be changed."
 

Jim Wynne

Staff member
Admin
#14
Re: Major interpretation problem w/ customer

Yep. The horse [Contract Review was missing] is dead - we can stop beating it.
While there might be no sense in continuing to actually flog the decedent, it can be useful to show neophytes the corpse as evidence of what can happen if we don't try to anticipate mistakes, misunderstandings and ambiguities.

FYI:
Typically, my experience with job shops and contract manufacturers is that they do not take an ambiguous note or dimension as carte blanche approval to FAR EXCEED the standard tolerances for the drawing. Thus said, I would have expected most shops to have interpreted the dimension (assuming no other customer interaction during Contract Review) as 0.460 +0.020/-0.000. This means the maximum part sent to the customer would have been 0.480.
There is absolutely no basis for assuming that a bilateral block tolerance may be converted to a unilateral tolerance equal to the bilateral spread (or anything else) under any circumstances. In this case, the customer got what he asked for. You don't contradict your own block tolerance unintentionally. The customer assumed that some measure of restraint would be invoked, but didn't bother to define the allowable extent. Note also that the OP has stated that the customer approved the part five years ago. Like I said earlier, sometimes you have to eat some unpalatable meals in order to keep the peace, but given the evidence at hand, there's little doubt that the specification was met.
 
B

branham91

#15
Look closer in notes on the drawing. There may be a statement that says "All dimensions +/- .010 unless specified otherwise" I would not put much stock in the +/- .010 tolerance because it sounds like a generic tolerance just placed in the title block. I would make sure the part does not go below .460 for sure and not over .470 if you are capable. It would be good to do a cpk for that feature then provide the customer with the data that corresponds to lowest scrap tolerance for you vs what they actually deem as critical specs.
 

QMMike

Involved In Discussions
#16
I really appreciate everyone's feedback. Thankfully this is not an automotive customer (which had it been, knowing my automotive customers I don't think this would have ever happened). This customer however typically used drawings as reference believe it or not. They have since the advent of our dealings with them, gotten better.

Oh yeah - I forgot to mention... at my customer's initial contact to me upon this "rejection" they said the wall thickness was too thin. When I asked what they were measuring it to be they stated - .052 / .058. In the note section of the drawing it states: ".060 Wall (Except where noted)" - there is a section of the part that is supposed to be .040. Again, the block tolerance is all you have to fall back on and it states for an extrusion +/- .010. I told them good, then those parts are within spec. - They didn't like that response and said that we shouldn't have "assumed" the wall had a +/- .010 tolerance. In my opinion, with all that I've stated about the drawing, the drawing is clear - basic blue print reading - nothing was assumed and the drawing was taken at face value.
 

Coury Ferguson

Moderator here to help
Staff member
Super Moderator
#17
Oh yeah - I forgot to mention... at my customer's initial contact to me upon this "rejection" they said the wall thickness was too thin. When I asked what they were measuring it to be they stated - .052 / .058. In the note section of the drawing it states: ".060 Wall (Except where noted)" - there is a section of the part that is supposed to be .040. Again, the block tolerance is all you have to fall back on and it states for an extrusion +/- .010. I told them good, then those parts are within spec. - They didn't like that response and said that we shouldn't have "assumed" the wall had a +/- .010 tolerance. In my opinion, with all that I've stated about the drawing, the drawing is clear - basic blue print reading - nothing was assumed and the drawing was taken at face value.
Well, all I am going to add is: The customer has specified the requirements. They said it wasn't good.

This should be the ultimate answer (empasis added in bold), unless you are able to prove otherwise, using the Customer's drawing standard or something more concrete, in my opinion.
 

Jim Wynne

Staff member
Admin
#18
Well, all I am going to add is: The customer has specified the requirements. They said it wasn't good.

This should be the ultimate answer (empasis added in bold), unless you are able to prove otherwise, using the Customer's drawing standard or something more concrete, in my opinion.
While the ultimate answer might be giving in and making the customer happy, there comes a point when we have to assume that the customer specifications mean what they say. Customers must never be allowed to continually make suppliers pay for their mistakes. A line must be drawn somewhere, and if you keep letting them get away with it, they're likely to keep doing it. At this point, there's no telling with any of this customer's drawings whether what they're asking for is what they actually want.

While some of this can be mitigated by conscientious contract review, if there's no reason to question a specification, contract review isn't going to help. The customer isn't always right, and when they've evinced a pattern of being wrong, someone needs to put a stop to it.
 

Coury Ferguson

Moderator here to help
Staff member
Super Moderator
#19
While the ultimate answer might be giving in and making the customer happy, there comes a point when we have to assume that the customer specifications mean what they say. Customers must never be allowed to continually make suppliers pay for their mistakes. A line must be drawn somewhere, and if you keep letting them get away with it, they're likely to keep doing it. At this point, there's no telling with any of this customer's drawings whether what they're asking for is what they actually want.

While some of this can be mitigated by conscientious contract review, if there's no reason to question a specification, contract review isn't going to help. The customer isn't always right, and when they've evinced a pattern of being wrong, someone needs to put a stop to it.
I was not arguing that point. As you can see, I also stated that unless you can prove otherwise, using the Customer's Drawing Standard or something more concrete, how is the determination that the customer is wrong?

I have challenged numerous customers errors, but I have supported that with documentation.
 

Helmut Jilling

Auditor / Consultant
#20
While the ultimate answer might be giving in and making the customer happy, there comes a point when we have to assume that the customer specifications mean what they say. Customers must never be allowed to continually make suppliers pay for their mistakes. A line must be drawn somewhere, and if you keep letting them get away with it, they're likely to keep doing it. At this point, there's no telling with any of this customer's drawings whether what they're asking for is what they actually want.

While some of this can be mitigated by conscientious contract review, if there's no reason to question a specification, contract review isn't going to help. The customer isn't always right, and when they've evinced a pattern of being wrong, someone needs to put a stop to it.

I definitely agree with your philosophy. The customer-supplier relationship has gone out-of-kilter, and it is time the industry tries to bring some reasonable balance back to it.

However, we have to pick our battles, and in this case, I think we have agreed the supplier failed to do proper review of the drawing. So, this case might not be the right battle to apply your philosphy.
 
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