It’s the Other Stuff that’s the Problem
Sometimes you have to start looking at the less obvious culprits.
Sometimes all the usual steps taken to resolve measurement disputes still don’t point to a culprit you can deal with. But one certainty always remains: Your customer insists their gages are right so the problem must be due to your gages. Your customer may not have a reasonable technical basis for such a claim but since they pay the bills, many companies caught up in such a situation may try a political way out of it.
What’s politics got to do with this, you may ask? Many companies deal with the situation the way politicians deal with awkward situations: They focus on the process irrespective of the problem so they can be seen to be doing something even if it has nothing to do with the real problem. In their case, they have very deep pockets (yours) to provide cash they can splash all over the situation to show they’re doing something. Unfortunately, private companies can’t get off the hook so easily.
In our case, the political way of dealing with the situation is to forget about finding the cause and deal with the effect. If your parts won’t assemble with your customer’s components, get rid of the gages and keep adjusting the size(s) until they do. Problem solved—for now—but sooner or later reality will come back to haunt everyone so it’s better to get it all sorted out at the beginning.
As I mentioned at the start, sometimes you go through all the steps and no answers are forthcoming that you can work with. This usually means it is other stuff—beyond the obvious—that has to be dealt with.
A while back one of our customers faced a similar situation but fortunately for them, their customer wanted to sort it out as much as they did.
The component in question was a threaded rod that would not assemble with a mating nut made by their customer. Both companies had their gages calibrated and the results indicated both were suitable for the task at hand. Optical inspection did not reveal anything of note and neither did alternate methods of directly measuring the components.
Since we had supplied the gages to the subcontractor who had provided the details they were made to, we suspected that there had been a transcription error. Also, there was a possibility that the specs for the mating parts may have had a minor error that was now causing everyone a headache. So we asked for the drawings for both parts which were checked out and we came up with nothing. The data transfers were accurately done and there was no conflict between the part specs.
As a desperate last move, we did what many people do in these situations: blame the gages. But since we had recalibrated our customer’s gages we suspected the problem may be with their customer’s gages that were supplied and calibrated by another facility. Their customer kindly agreed to let us have a look and sent them to us. The answer to the problem was evident when we opened the box. They were over twice the length of those our customer ordered which pointed to a linear pitch error on the component the standard length gages would not pick up. Direct measurements of pitch on the component confirmed our suspicions.
The end user of the components had followed a basic rule in gage selection which states that the best gage duplicates the shape, size, etc., of the component to be checked. Our customer was not advised of the need for this and had ordered regular thread ring gages.
I’m not sure how our customer fixed the pitch error problem, but he ordered a set of gages the same length as his customer’s gages and they lived happily ever after as far as I know.
For most measurement or gaging disputes there is usually one or two obvious probable causes that can be checked out without decimating the budget. But when the usual suspects are found to be innocent, you have to start looking at the not so obvious. The other stuff that most will consider a waste of time checking out—but often isn’t.