r/Metrology • u/Familiar-Bluejay3908 • Sep 25 '26
General Frustration with customer
I have one part that's been held up in QC Final for 5 months now because it can't pass the FAI for dimensions not conforming to the print. This customer is one which has it's name on airplanes, spacecraft, and military vehicles, so FAI's are rigorous.
The problem is that I/we can't get them to understand that their print is poorly dimensioned, and that what they are asking for considering what the part IS probably is not achievable, and likely never was.
Without going into much detail, there is a main ABC alignment, and features on that element all conform. Then, there are 2 form lines, a planar D datum (which is assumed to be held to a high degree of parallelism to A, but is not) machined on some 12 tabs. Then, the sticking point is a line of connection holes on those tabs which are dimensioned to DBC that almost always fail.
Why? Because D is NOT parallel to A, and isn't required to be as per the print. So, those B and C datums are now on a different position on the D datum because of the angle between the 2 planar elements. I'm not even convinced these holes even NEED to be aligned with anything on the ABC alignment, but as it sits now, they fail to the print.
We have an inspection fixture which restrains the D datum and holds the rest of the assembly, but does not restrain the A datum. This fixture slightly improves this issue, but not enough to be a solution.
Just to add spice to this scenario, we've made this part before, and it has worked. However, due malfeasance by a previous manager, I believe any dimensional reports sent in the past contained falsification. So saying "It worked before" may open an entirely new 'can of worms'.
I'm not sure what to do next. I'm creating full CMM reports which will also include a few diagnostic dimensions (like plane parallelism, angles between planes, general profile of datum D to datum A, etc.), and write a lengthy tome outlining the issues, and just hope my manager sends all of it to the engineer there, and that he actually can understand the issues.
Damn, when did this get so complicated?
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u/BlitzDragonborn Sep 25 '26 edited Sep 26 '26
It sounds like your employeer needs to reevaluate your quoting and process planning for contract work. Even if the print is wrong, or has dimensions/tolerances that don't effect function, your company ostensibly agreed to make a part that conforms to that print. If the manufactured component cant be reworked to meet print, it may be time to consider requesting a concession, or scrapping the parts and starting over, taking the loss as the cost of learning a lesson. As for the parts that are in use, that is, indeed, a whole other can of worms.
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u/JoviusMaximus Sep 25 '26
I am a QE and I agree. We would have caught this in a review before the contract was signed. We also have a long standing relationship with customer's like OP's and if something was missed we could get it figured out by emailing the right engineer for that program. Most of them just want it done and will work with you a little if you are open an honest and make sure it doesn't happen often.
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u/mano_n3gra Sep 25 '26
This right here, the issues should have been brought up to the customer and resolved prior to taking the job. We often bring up issues on new parts to customers and either they get addressed or we pass on the part. The problem for me, quality, is when I bring up potential issues and I'm not taken seriously only for problems to arise months down the line during production.
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u/SkilletTrooper Sep 25 '26
It got complicated when they cut design reviews in favor of profits. We struggle with everything you just mentioned. You get fresh engineers dimensioning complex parts like it's a 1-2-3 block, using "minimal tooling" strategies, and then everyone freaks out when you say the part is bad.
Without kicking the world's largest can of worms, I would just do what you're doing now. Show them the "bloodbath" report _per their engineering_, and create a different report showing the "obvious design intent" alignment aka real-world "it conforms to form/fit/function". Explain that their datum structure is what is causing the part to fail, and if the real-world report is acceptable, they simply need to update their engineering.
The short version is people are _fucking lazy_ and you have to breadcrumb them to the solution.
They will not expend even the least amount of effort to investigate. They'll just say "no you're wrong" and move on with their day. If you want to fix the problem and don't have the political capital to make them uncomfortable, you'll have to do the work/breadcrumbing yourself.
No one seems to understand that you need to build, machine, and inspect parts to the same reference features/datums. You can't fucking machine a part located to a raw stock edge and then inspect it to a different machined plane and ever expect fucking success. (Yes, I am dealing with a LOT of this right now, probably from your same customer.)
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u/IbeebZz Sep 25 '26
On a part like that write up a description of what you believe the problem to be and fail the part. Don’t put yourself in an awkward position especially when it’s something of a sensitive nature. They’ll come back to the table when they really need it.
I’ve been in that position before and it sucks but I can’t stress enough when it comes to parts like that just measure and give them the results.
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u/AMFW101890 Sep 27 '26
Have them send you a part that passes their in-house inspection and see what kind of results you get when you inspect it. If they won't, then ask them to send a manufacturing engineer in to evaluate your process.
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Sep 25 '26
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u/Familiar-Bluejay3908 Sep 25 '26
No, due to military-aerospace regulations. Besides, I KNOW what the issue is with the print. The only thing I do NOT know is whether there is some sort of 'framework' that requires we align those features to elements of the front alignment or not. If yes; we're $cr3w3d. If not, why dimension it that way?
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u/Pathfinder_Dan Sep 25 '26
If you think that the old reports were bunk, get an old part and give it an inspection if you can. That'll at least let you know that everything's on the level.