Pin Gage Calibration - Pins seem to be "growing"

S

strange1

#1
I am presently calibrating our sets of pin gages using a Pratt Whitney labmaster. I'm seeing many pin gages that are OOT. this is not a surprise, the odd problem i'm having is they are OOT larger than previous calibration certs. I am comfortable with my uncertainty, and process. The OOT's are not obvious. I.E. one series all large, corrosion.

I am compensating for temperature, and am using a standard which is adequate.

has anyone encountered pin gages which grow?

These are Grade 2 Fowler steel, .501 to .625 pins, Plus.

I'm calibrating to +.0002"

.507 nominal 4/7/2011 as found .50720
same pin 3/15/2013 as found .50727
 
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Jim Wynne

Staff member
Admin
#2
Re: Pin gage Calibration

I am presently calibrating our sets of pin gages using a Pratt Whitney labmaster. I'm seeing many pin gages that are OOT. this is not a surprise, the odd problem i'm having is they are OOT larger than previous calibration certs. I am comfortable with my uncertainty, and process. The OOT's are not obvious. I.E. one series all large, corrosion.

I am compensating for temperature, and am using a standard which is adequate.

has anyone encountered pin gages which grow?

These are Grade 2 Fowler steel, .501 to .625 pins, Plus.

I'm calibrating to +.0002"

.507 nominal 4/7/2011 as found .50720
same pin 3/15/2013 as found .50727
How long has this growth been going on? If you have a significant number of pins that have "grown," and the phenomenon is seen only in a single set of two as-found measurements, I think you have a measurement problem, assuming that you've controlled for temperature/RH.
 
S

silentrunning

#3
Re: Pin gage Calibration

I think Jim is right. I would suspect the measurement more than the pins. I have a personal set of Starrett pin gages (.062" to .250") that is over 25 years old and when I send them out for calibration they have never varied. They are kept oiled and wrapped when not in use. I would look into the repeatability of the labmaster first.
 

Kales Veggie

People: The Vital Few
#4
I am presently calibrating our sets of pin gages using a Pratt Whitney labmaster. I'm seeing many pin gages that are OOT. this is not a surprise, the odd problem i'm having is they are OOT larger than previous calibration certs. I am comfortable with my uncertainty, and process. The OOT's are not obvious. I.E. one series all large, corrosion.

I am compensating for temperature, and am using a standard which is adequate.

has anyone encountered pin gages which grow?

These are Grade 2 Fowler steel, .501 to .625 pins, Plus.

I'm calibrating to +.0002"

.507 nominal 4/7/2011 as found .50720
same pin 3/15/2013 as found .50727
You probably already checked:

- same master? no change?
- same Labmaster? no change? no repair
- only this pin set?
- rechecked calibration results from last week? last month?

Old thread: http://elsmar.com/Forums/showthread.php?t=35058

More reading: http://www.ring-plug-thread-gages.com/ti-gg1-Hardened-Steel-Growth.htm
 
S

strange1

#6
There are only two sets of cal records for these. One from 1990's and one from a local cal house in 2011.

The pins which are in question (perhaps 5-8 in a set of 144) were marginal when done by the local cal house. I.E. .501 Nominal, recorded as .5012 in 2011. Now on the Labmaster reading .50124. I think the "rounding" is the issue.

I've mastered the Lab Master and did a "confidence" check using a Sylvac S_Mike Pro, 4 1/2 digit resolution. As well as a Mitiuoyo mic. While the resolution isn't there they both confirm the pins are indeed not to spec.

The pins are listed as Grade 2. I believe that is .0002 accuracy from all that I can find. I can't find any records of a lower class pins...giving a beifit of a doubt to the records.

I've done an R&R, as well as calculated the uncertainty of the Labmaster, and can repeat the measurements.

temp 68?, wich 24 soak time. RH is 24%... go figure, Indy in the winter time

Just seems odd....:frust:
 

Jim Wynne

Staff member
Admin
#7
There are only two sets of cal records for these. One from 1990's and one from a local cal house in 2011.

The pins which are in question (perhaps 5-8 in a set of 144) were marginal when done by the local cal house. I.E. .501 Nominal, recorded as .5012 in 2011. Now on the Labmaster reading .50124. I think the "rounding" is the issue.

I've mastered the Lab Master and did a "confidence" check using a Sylvac S_Mike Pro, 4 1/2 digit resolution. As well as a Mitiuoyo mic. While the resolution isn't there they both confirm the pins are indeed not to spec.

The pins are listed as Grade 2. I believe that is .0002 accuracy from all that I can find. I can't find any records of a lower class pins...giving a beifit of a doubt to the records.

I've done an R&R, as well as calculated the uncertainty of the Labmaster, and can repeat the measurements.

temp 68?, wich 24 soak time. RH is 24%... go figure, Indy in the winter time

Just seems odd....:frust:
What you have there are "plus" pins. They're deliberately oversized, so a measurement of .0002" over the nominal size is to be expected. There are also "minus" sized pins. Unless the fifth decimal place is significant in your applications, I wouldn't be too concerned about it.
 
S

strange1

#8
i understand, the errors I'm seeing are .00027, .00028 etc. etc. While not significant, they are still an OOT
 
K

kgriff

#10
I realize this is a somewhat old post, but I have a possible reason that hasn't been mentioned.

There is another phenomenon that you could be experiencing in which steel does, in fact, grow over time. Depending upon the heat treat/quench process used in the manufacture of the pins, the steel could grow. Heat treating and quenching is designed to stress-relieve the metal, as well as harden. If the heat treat/quench is not done properly, the metal will naturally stress relieve over time. This natural stress relief can result in gage growth.
Based on what I've seen over the years with X class plug gages, I don't think 0.00007 growth over two years would be completely out of the question. I also think that the storage and use conditions of the gages can effect the amount of growth. (Again, this is only if the metal was not properly stress relieved.) I have no empirical evidence to support this theory, but it seemed to be the case in our shop.
We have somewhere around 8,000 X class plug gages and, for the older gages, we have observed growth in probably 10% of them. It seems that newer gages are better stress relieved.

If you want a better/more technical explanation, check with any metallurgist.
 
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