HAS ANYONE EXPERIENCED THE PHENOMENON OF FAILED PLAIN PLUG GAUGES, SPECIFICLY THE NOGO MEMBER WHEN THE RESULTS SHOW THAT THE GAUGE HAS GROWN IN SIZE? WHAT I'M TALKING ABOUT IS A GAUGE WITH A .00006" TOL. AND THE RESULTS SHOWING THE GAUGE TO BE OVERSIZE BY .00002". THE GAUGE IS A CLASS "X" AND HAS PASSED CALIBRATION FOR THE PAST 3 YEARS. I CALL THIS A PHENOMENON BECAUSE THEORETICLY THE NOGO MEMBER NEVER ENTERS THE PART BEING CHECKED. I WOULD ALSO MENTION THAT THE SAME OUTSIDE CALIBRATION LAB HAS PREFORMED THE CALIBRATION FOR THE PAST 4 YEARS. CAN ANYONE SHED SOME LIGHT ON THIS SUBJECT FOR ME? ANY INFORMATION WOULD BE APPRECIATED.

Scott is it possible that the plug has been damaged in some way (ie dropped and/or burred from forcing) by mishandling? If not then I would get another opinion...could it have been cal tech dependant? perhaps the cal lab needs to be involved my guess is the correct tolerance wasn't enforced on the tool used to cal with.. for 3 years if there is no signs of mishandling? What about env conditions and the standard, at that tolerance could that have been a factor?

My guess is you will never know..... if the lab is at fault.

BARB THANK YOU FOR THE REPLY. THERE IS ALWAYS THE POSSIBILITY OF UNDETECTABLE DAMAGE. I CHOSE TO CONTACT THE LAB AND HAVE THE CALIBRATION PREFORMED AGAIN BY ANOTHER TECH.

Do let us know what happens.

Scott,
Maybe the Lab "Soaked" the gage in a temperature higher that normal. The growth usually is caused by the steel expanding.
Just a thought.
Ron Taylor

right ron...forgot that one....

THANKS RON,
BOTH GAUGES IN QUESTION HAVE CERTIFICATION SHOWING THAT THE TEMP AT CALIBRATION WAS 70 DEG. I BELIEVE THAT SHOULD BE A NORMAL RANGE. PAST CALIBRATIONS WERE CONDUCTED AT 68 DEG.

WELL EVERYONE, I RECEIVED MY GAUGES BACK FROM MY CAL LAB. I FEEL THE RESULTS ARE INCONCLUSIVE. AS IN ANY MEASURMENT THERE IS VARIATION. THE SAME TECH CALIBRATED THE GAUGE THIS WEEK AND LOW AND BEHOLD THE RESULTS ARE .00007" DIFFERENT. THE GAUGE PASSED CALIBRATION EXCEPT FOR THE GO MEMBER WHICH IS STILL OVERSIZE. THE CAL TEMP WAS 3 DEG DIFFERENT. I WOULD PRESUME THAT A GO GAUGE COULD GROW BY MATERIAL SLOWLY WEARING ONTO THE GAUGE AS IT IS PASSED IN AND OUT OF MANY PARTS. THIS HOWEVER STILL SHEDS NO LIGHT ON MY ORIGINAL QUESTION THAT HOW CAN NOGO MEMBERS GROW, NOT ONLY PLAIN PLUGS BUT ALSO ON THE NOGO MEMBERS OF THREAD GAUGES THAT NEVER ENTER A PART? THIS IS NOT A NEW PROBLEM BUT A DILEMA THAT HAS COME UP TIME AND AGAIN. NOW WHAT?

Might I suggest checking a gage when first receiving it. It has been my experience that some gages are made on the high side to allow a longer life time. When I check incoming gages I also have to allow for uncertainty of the equipment that first certified the gage and then my own equipment. Hope this helps. :cool:

I see quite a few growing gages, especially cylindrical plug gages in larger sizes. Aside from being dropped I have seen a number of oversize gages in trilock handles where the bolt is overtightened and the plug gage bellys out in the middle. The Size Control Company used to make a plug gage lapper that would help correct some of the growing gage issues.

Hardened steel does have the propensity to grow. The growth is usually noticed in larger sizes because it is an in/in type growth. I do not know the size the gage in question, but if it is noticeably growing I expect that it is over an inch in diameter.

What happens is when the steel is hardened the modules are trapped in stasis. Slowly the molecules relax and as they relax they cause an expansion of the material. The gradual relaxation process takes about a year. The larger size the more the change is noticed. The tighter the tolerance the more the movement is noticed.

To combat this phenomenon gage makers require that their hardened steel be triple cold stabilized. The process requires the gage to be cycled three times through a freeze/thaw process. This procedure will reduce the probability of gage growth. Note the use of the word “reduce” instead of “eliminate”.

Hardened steel does have the propensity to grow. The growth is usually noticed in larger sizes because it is an in/in type growth. I do not know the size the gage in question, but if it is noticeably growing I expect that it is over an inch in diameter.

What happens is when the steel is hardened the modules are trapped in stasis. Slowly the molecules relax and as they relax they cause an expansion of the material. The gradual relaxation process takes about a year. The larger size the more the change is noticed. The tighter the tolerance the more the movement is noticed.

To combat this phenomenon gage makers require that their hardened steel be triple cold stabilized. The process requires the gage to be cycled three times through a freeze/thaw process. This procedure will reduce the probability of gage growth. Note the use of the word “reduce” instead of “eliminate”.


Wayne:

GREAT first post!!!! Welcome to the Cove!

Craig

I, too, am impressed with this little bit of metallurgical legerdermain!
Who knew? (Let alone "suspected" such a thing could be?)

I gave you some "karma" for this helpful addition to our knowledge base. To see exactly how much, click on "User CP" in the navigation bar near the top of this page.

Welcome to the Cove!:bigwave: We'll be looking for more good things from you.

Not something I'd expected to find in a material such as steel, but common in plastic processing and called molded-in stress. It's very common for plastic parts to slightly change in size just over time after molding, and more profoundly if the part is subjected to environments of high moisture or heat. The heat allows the molecules in plastic to relax and relieve the locked-in stress.
Very interesting to find out that steel can show similar properties.

What happens is when the steel is hardened the modules are trapped in stasis. Slowly the molecules relax and as they relax they cause an expansion of the material. The gradual relaxation process takes about a year. Ah.... Ok, I did know that this can happen and have seen examples, but nobody ever explained it to me before. Thank's Wayne.:agree1:

Furthermore: This can serve as food for thought for anyone who believes that there is no need to calibrate a tool that has not been in use. Std comment: -That is not necessary. It has not been out of the box, so what could possibly have affected it? Well, something could...

/Claes

This can serve as food for thought for anyone who believes that there is no need to calibrate a tool that has not been in use. Std comment: -That is not necessary. It has not been out of the box, so what could possibly have affected it? Well, something could...

/Claes

The probability of growth is most likely noticeable:

1. If the gage is over an inch in size. Because the growth is compounded as size gets larger it will be more apparent. On smaller tools the growth will most likely be considered within the range of uncertainty or be explained away as being from different technician/equipment/laboratory variation.

2. In the first year after it has been hardened. Most of the movement is aged out of the steel after the first year. Things like temperature variation and gage use will encourage faster aging. Being unused and in a box may encourage slower aging to a small degree. Any growth detected after the first year will most likely be considered within the range of uncertainty or be explained away as being from different technician/equipment/laboratory variation.

I knew about expansion coefficients in high temperature environments and the subsequent need to control inspection lab environment, but I hadn't yet heard of the molecule relaxation phenomenon. Thanks for such excellent input, and welcome to The Cove! :bigwave:

I just read this posts and found out that I encountered the same situation back in 2001. Three things:
1) You gauge the Laboratory who conducted the Calibration by conducting an audit in the laboratory sight or at least talk to an official. Know whether they are practicing a valid calibration procedure (ASTM, ANSI,etc. where these standards require specific controlled calibration laboratory conditions like Temperature and Humidity) and know whether their calibration personnel have sufficient training and education.
2) Submit the gage to a different calibration agency (If resources are available otherwise, in-house observation). Compare the result to the first calibration.
3) Decide if you will replace this Agency based on the results of the two items above otherwise this event might happen again and your product quality inspection activity can be inaccurate.

1) You gauge the Laboratory who conducted the Calibration by conducting an audit in the laboratory sight or at least talk to an official. Know whether they are practicing a valid calibration procedure (ASTM, ANSI,etc. where these standards require specific controlled calibration laboratory conditions like Temperature and Humidity) and know whether their calibration personnel have sufficient training and education.
This should be done before deciding on a calibration source, of course.
2) Submit the gage to a different calibration agency (If resources are available otherwise, in-house observation). Compare the result to the first calibration.
Having two different sources check the same gage and get different results tells you only that one or both of them are wrong.
3) Decide if you will replace this Agency based on the results of the two items above otherwise this event might happen again and your product quality inspection activity can be inaccurate.
Wayne provided what appears to be the most likely explanation; your first two items, while providing additional evidence, likely won't provide enough to make a decision on sourcing.