Calibrating adjustable thread ring gages can get a bit sticky on occasion due to customer assumptions versus the requirements of ISO 17025. It takes a lot of diplomacy to sort out situations where this type of gage is involved due to the number of phantom setting plugs drifting around inspection departments all over the country.

Since we provide an accredited calibration service for such gages, customers assume that we can do so all the time. This is not a problem where the threads involved are standards as are the setting plugs used to check them. When this is not the case, most customers will understand that we cannot stock special setting plugs and provide one they may have on hand for their special rings.

Having done their duty, most customers feel that’s the end of it and await the return of their gages with an accredited report. It gets sticky when you have to advise them that since their setting plug has not been calibrated, we cannot issue an accredited report. Once more they may understand the reasons for this and get the setting plug calibrated at the same time. Others may not be so enlightened, especially if our calibration of the setting plug indicates it is less than stellar when it comes to accuracy.

Some customers figure they’ll sort this problem out once and for all and they then proceed to order a new setting plug from the maker of the thread ring gages. The fact that the rings they purchased were probably not set to the setting plug now being made to order is another can of worms I’ll leave for another day.

As happened recently, the setting plug arrived along with the maker’s calibration report and we had to advise the customer he is still not out of the woods. Why? The maker’s calibration facility is not accredited so the plug cannot be used as is to produce an accredited report. We could issue a report noting that the customer’s setting plug was used for the work but it would not be an accredited report.

As an aside, I noticed that the maker’s report indicated their work was traceable to NIST. But the warm fuzzy feeling this provides was suppressed by the fact the NIST report was eight years old. To make matters worse, it noted that the ‘lead’ was ‘within tolerance,’ not what it actually was. Similarly, the thread angle was also shown as ‘in tolerance.’ As a result, no approximation of a functional pitch diameter was possible, rendering it next to useless for the task at hand. On the plus side, the pitch diameters quoted were shown to be perfectly parallel on a four inch diameter gage. I can’t recall the last time I saw this. Okay, I can’t recall ever seeing it, but since the data was reported to only four decimal places, it’s possible it’s not as parallel as the numbers indicate.

At the end of all of this, the customer decided to have us calibrate the setting plug and that brought a sigh of relief. Unfortunately, this will probably eat up all those dollars he claimed he saved buying the gages based on price in the first place. After all this messing around, it would appear we’re now good to go—aren’t we? Maybe yes, maybe no.

If our calibration of the setting plug indicates it is not as good as the maker claims in his report we may have to go back to the customer yet again. Obviously, if we do, we’ll look like the bad guys when all we’re trying to do is issue a properly accredited report the customer has requested.   

All of this extra work means extra costs to both the customer and the laboratory involved. And it also means delays in getting the gages calibrated. There are other issues I haven’t touched on that could further mess up what started out as a simple project but since I’m a simple guy, I’ll leave them for another day.

 The way to avoid this situation is relatively simple. If you are buying special rings, get them and their setting plugs calibrated from an accredited source at the beginning. And remind your purchasing people that there’s a reason some folks are cheaper than others. Sometimes you just can’t afford the ‘savings.’