I am looking for feedback on how people approach the calibration of thread ring gages. My experience has been to return them to the manufacturer. I am really looking for a faster and more economical approach. I have approximately 200 sets of thread ring gages in my database. All comments would be appreciated.:)

I am looking for feedback on how people approach the calibration of thread ring gages. My experience has been to return them to the manufacturer. I am really looking for a faster and more economical approach. I have approximately 200 sets of thread ring gages in my database. All comments would be appreciated.:)

We return our ring gages for calibration. Our schedule rotates the sets so we are never without calibrated sets.

I suppose, depending on the criticality if the measurement, you could verify the gages in-house. Buy a master set of calibrated plug gages and verify the ring gages internally. That way you would only need to send out the master for calibration. 200 sets may be pushing the limits of the master set though so you may have to calibrate it more often.

Dave

We return our ring gages for calibration. Our schedule rotates the sets so we are never without calibrated sets.

I suppose, depending on the criticality if the measurement, you could verify the gages in-house. Buy a master set of calibrated plug gages and verify the ring gages internally. That way you would only need to send out the master for calibration. 200 sets may be pushing the limits of the master set though so you may have to calibrate it more often.

Dave

Your suggestion would pass an ISO 9001:2000 audit?

Rather than thinking of it as one set of 200 gages, think of it as 200 ring gages. Are all used at the same degree? If not, calibration could be set differently for various sizes, which might save a substantial amount.

FWIW:
My [relatively] small shop specializing in turning had as many as 20 or 30 tapered pipe thread ring gages for each size thread we ran, all mastered to the same plug master at the manufacturer (retained for our use only.) We had two or three on-site master plugs made as identical as possible to the manufacturer's master. We contracted with our customer to use gages also made and calibrated to the same master by our manufacturer. We would only have one ring gage for each machine running a specifc size thread. We would check each active gage every shift against our plug master. Any discrepancy got that ring taken out of service and cycled to the manufacturer for evaluation and either refurbished, calibrated and certified OR destroyed.

Because we had different size runs, setting refurbish/recalibrate by calendar instead of actual wear was not practical.

Our customers followed a similar policy. Having an ample inventory meant we ALWAYS had certified calibrated rings and never had to rush the manufacturer or deal with rings not calibrated to our "special" master.

OFF TOPIC::topic:
we used stepped gages for tapered threads. The link may not be the best explanation, but it's the first I googled. http://welcome.gsgage.com/Tech%20CD%20Rev%201.0a%20PDF/4.1_Pipes.pdf

I can see that I need to ask the question a little differently. Is there another way to calibrate thread ring gages? I find that using "set masters" is very subjective. It is almost imperative that they be checked to the master used to manufacture them. I find it hard to believe that 2 people using the same master could come up with the exact same numbers when calibrating a thread ring gage. From what I have learned the pitch is never measured, it is more of a "feeling" on a set master. Am I beating a dead horse here?

Proper calibration of thread plugs, unless they are really really coarse, is accomplished using a supermic.....the environment is 20 C +/- 1 C, RH usually between 35-45%.....in other words.....

Send them to a calibration laboratory that is accredited to ANS/ISO/IEC 17025 for thread plugs, and have metrology professionals calibrate them.

The argument here for having metrology professionals calibrate your items instead of your folks calibrating them, is exactly the same as having machinists operate the CNC (or similar machines) instead of having the shipping clerk run them.....the metrology professionals have the proper equipment and environment, and the training and experience to make effective use of them.

Hope this helps.

Hershal

I am looking for feedback on how people approach the calibration of thread ring gages. My experience has been to return them to the manufacturer. I am really looking for a faster and more economical approach. I have approximately 200 sets of thread ring gages in my database. All comments would be appreciated.:)

We calibrate the majority of ours in-house using master plugs. It works for us.:agree1:

Russ

I was always a great one for "division of labor" and never had any hesitation about outsourcing tasks outside of our core proficiencies. I could have easily put in a system to apply electroless nickel plating, but it would have meant nothing to our bottom line and very little to our quality, since we were very good at selecting competent suppliers of such service. Similarly, I have written elsewhere about dumping our grinding operation and getting better service in return.

Similarly, even with hundreds of plug and ring gages in addition to 3-wire mikes, snap ring gages, etc., I never found it cost-effective to even consider doing our own manufacture, refurbish, etc. It was sufficient for our purpose to check only active ring and plug gages against masters before each shift. If they didn't pass this perfunctory review, we put the problem in the hands of specialists and moved on to the next gage, since we only got paid for pieces we delivered to customers and preferred to devote our time and energy to that.

We do not return thread gauges to the manufacturer. We have master thread plug gauges to check calibrated thread ring gauges & vice versa. All the gauges are spread over a year , hence we do not have issue of faster checking. It has not created any issue during ISO audit.

Your suggestion would pass an ISO 9001:2000 audit?

I can't think of a reason why it wouldn't. Do you know of something in ISO 9001:2000 that would rule it out?

Dave

Regarding the decision to return your gauges back to the manufacturer for calibration of do it yourself. It all depends on what equipment you have now and what skills you have available. If you have the equipment and skill set in your team, then I sure you can calibrate the critical gauges in house (provided you have the time). If not you are looking at purchasing a suitable calibration equipment, delivery times, training . . . .

I had a QC department that held 2500 (sets) of both plug and ring gauges and decided that sending them out for calibration was the simplest option, I could have done it in-house but I thought with the amount we had, we could meet ourselves coming back, if you know what I mean. Also, I would never send it back to the manufacturer they are always more expensive then calibration houses.

This yearly calibration thing that people keep mentioning, gets my back up does that, you calibrate as and when required and not to any scheduled timeframes. I had a new production manager that once came down and asked why some of the gauges were calibrated every 7 years, and insisted I changed it because we would pass ISO audits. I passed him the ISO manual and asked him to highlight for where it stated I had to calibrate my gauges at set timeframes, obviously he couldn’t.

Another thing, all it states is to ensure the method of measuring is suitable for the job at hand. To me that means initial gauge studies (via the MSA principle) and conduct health checks should it need it.

Regards

Lee01

We do not return thread gauges to the manufacturer. We have master thread plug gauges to check calibrated thread ring gauges & vice versa. All the gauges are spread over a year , hence we do not have issue of faster checking. It has not created any issue during ISO audit.This raises a question of what folks mean by "calibrate"

To me, calibrate means to make a notation how far off an instrument or gage reads versus the master standard against which it is compared. With that notation, the readings with that gage against workpieces are similarly adjusted.

In my practice, if a gage had a variance with a master, it was taken out of service and sent to the professional service. We did NOT BREAK the seal on the adjustment screw of a ring gage to "make it fit" the master.

What do the rest of you understand by the term "CALIBRATE?"

I agree with your understanding. We do pretty much the same thing.

I would like to point out though that outside the "Lab Arena" the terms calibration and verification are used pretty much interchangeably. When we "calibrate" a gage against a master, in many cases we are really verifying the accuracy of the gage. Like Wes, if the "calibration" couldn't be verified, we would take it out of service and send it to a cal lab.

We would never break the seal and make an adjustment on a ring gage either.

Dave

What do the rest of you understand by the term "CALIBRATE?"

We've done this many times. Calibratrion is comparison to an accepted standard. How "accepted" is defined depends on the requirements. Calibration does not necessarily imply adjustment. Some things don't need to be adjusted after calibration.

When i was working with previous company,we use to send these thread ring gauges to external calibration lab which is certified under ISO/IEC 17025.But preciously this is not calibration,this is verification.

I agree "calibration" does not mean adjustment. "Adjustment" on a ring gage is a different animal from adjustment on an instrument to get zero and intermediate readings as on a vernier or micrometer when checking them with gage blocks. In Dave's view, with which I agree, we only verified the rings and plugs matched their masters.

Semi-:topic:
off topic
In my memory, we only had two causes of rings being taken out of service, other than normal wear:

Any dropping (reverifed with master before using again [absolutely no "baggage" for dropping one - stuff happens] bad results occur when operators feel they have to hide an accident.)
"Galling" when used on relatively soft workpiece material like aluminum, copper, or brass.Those two "events" don't happen on schedule to set a predictive time for calibration, refurbishment, or destruction. Hence the verification before each shift.

What do the rest of you understand by the term "CALIBRATE?"

ISO 9001, clause 7.6 clearly and consistently talks of calibrated or verified mmds. So they are obviously different activities. Verification has been defined by ISO 9000. That once again brings us back to the question put by Wes.

Calibration of an mmd is documenting the error in measurement by comparing it with standards traceable to the national ... with a known margin of uncertainty... ISO 10012 talks of it in much more detail. Unfortunately I dont have the latest copy (2003?) at hand. Maybe someone can quote from there.

Having known the extent of error in the mmd, whether the error is acceptable is a totally separate decision based on the requirements of the process for which it is used.

Repair is a totally separate story from calibration or verification. The device has to be recalibrated / reverified post repair.

Some practical examples / suggestions:

1. Different error level being acceptbale: A foundry and an attached machine shop. Vernier callipers considered unacceptable for use in the machine shop because of high error in measurement are passed on to the foundry for use without any adjustment or repair. They are perfectly acceptable for routine use here and are considered "calibrated" for the job on hand.

2. Gauges: Coming to the original problem relating the gauges, one practice followed by my clients (also by lee01) in such situations is to control the frequency of calibration based on use / wear pattern. Gauges in frequent use should be calibrated frequently. Those that are rarely used need not be calibrated at the same frequency.

And why calibrate the NO GO gauges at the same frequency as the GO gauges? They rarely wear out if at all. Such gauges need "maintenance" more than calibration. If at all, simple verification will do for them once in a while.

That reduces your workload (and costs) by half!

Think over it.

Calibration under internationally accepted definition means a comparison to higher level standards that are traceable through National or international standards to SI, with the traceability chain documented and uncertainty calculated at each step.

A perfect calibration does not require any adjustment.....in point of fact, most labs consider adjustment to be a repair, not part of calibration, unless the adjustment is incidental.

As for the original question in the thread, if the gages are compared internally, to actually consider that a clibration, the masters must be calibrated and the internal calibration records MUST meet the following requirements:
1. Document the certificate number of the last calibration of the masters (that is the link to the trceability chain)
2. Document the environmental conditions
3. Document the measurement uncertainty for the caliration of the gage that the record is for.
4. Then other requirements as appropriate.

Miss any of those requirements, in particular the traceability and uncertainty, and you have verification only, NOT calibration.

Again, send your gages to professionals.....and make sure the calibration provider knows what you need!

Hope this helps.

Hershal