Gage Pin Sets? Calibrate/Verify them all or just a sample size?

stevegyro

Involved In Discussions
#11
real good points on this forum. We use 'black oxide' pins which do show wear. This is a nice feature bc the visual is a clue for lab technicians to check size with a micrometer to verify, if the pin shows substantial wear.
 
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stevegyro

Involved In Discussions
#12
Thank you for the clarification @QCBOB .

So, the "FRO" sets in the shop are not used to verify product conformance? That is why they are marked "FRO" ?

F.R.O. could/may be interpreted differently, where "Use" means only for use, in the gage lab, by gage personnel.
(in earlier machine shop days) In other words, 'not for shop use' or "Gage Lab use only".

Thinking back to 'earlier machine shop days' , where gage pins, calipers, etc. would often be 'left out' in the machine shop:

In essence, the word "Reference" is an item (or an observation method- in nature), which we regard with authority.
Our confidence is based upon the quality of the References we have established.

To satisfy ISO 9001:2015 Clause 7.1.5.2 'measurement traceability' offers room for methodology, while maintaining the intent.

As a metrology practitioner, my interpretation (for practical implementation within budgets, real world, etc.), a some minimum requirements :

1. At least ONE calibrated 'variable measurement device', such as a 'Super-Mike', with known & stated accuracy as % Reading or % Full Scale.
2. Artifacts, such as gage blocks & gage pins, with known & stated accuracy, such as .040 thousanth's inch on XX plain plug 'pin' gage.
3. Error 'budget' which states- the NEEDED accuracy/precision requirements - BASED UPON Components that we produce, or receive and inspect.
4. Documentation for all gages used in producing parts for our customer: Certified Calibrations, Reference Calibrations, dates, serial no.'s, etc.
such that 'Reference Calibrations' can mean same as 'Verified' where our in-house metrology techs perform this-
PROVIDED THAT in-house metrology knows understands how much error is allowable in their process/products, and that the instruments
or calibrate artifacts (blocks, pins, rings) have much lower errors, such as 1/10th or 1/100th of the 'allowed error of production components'.
5. Caveat- GR&R studies clearly (and painfully) show that a very precise instrument, such as a digital micrometer reading out to 1/2 tenthou.
(50 millionths inch) is not guaranteed to always be accurate to one-tenthou. due to the person handling that micrometer.
Example: 'in-house' calibration of deltronic gage-pins using a hand held micrometer, is not advised. The opposite is more appropriate.

BR,
Stephen G.
Sr. metrologist
 
#13
We've also found it cheaper to replace the pin sets than to calibrate them. YMMV. Where we have calibrated them (prior employers) we treated them as a set, not individials.
A little late to the thread, but this seems risky as it never "closes the loop." A calibration represents a single moment in time, at the start of the interval. In addition to certifying the pin for use during the next interval, the recalibration (or verification) also confirms that the pin remained in tolerance throughout the calibration interval. Thus verifying the previous X months of measurements. If you purchase new instead of reverifying, you're only getting one half of the information.

Most places that I've worked, there was an evaluation that must take place if a gage failed its recalibration. With varying degrees of rigor, the process called for a risk analysis of the characteristics that the gage was used for in case there was any product recall decisions that had to be made (always deemed low risk).

If I just removed a pin set from the cal program and bought another, I wouldn't have evidence to claim that the pin remained in cal for the whole interval. So I would need to analyze past results.
 
#14
There's something that hasn't come up in this thread, but it bears mentioning. If pins are generally used to check low-risk things like clearance holes, there's no need to get excited about it. On the other hand, if there are close tolerances involved, pins are not a good idea but might be the only reasonable choice. If the product is being sold to a customer outside of your own, it's critical to find out how the customer is measuring. If the requirement is strictly internal to your company, it pays to determine whether the close tolerance is even necessary, and get agreement from the designer on the measurement method.

Here's an old thread on the subject: How can you justify using a more accurate Pin Gage class? (elsmar.com)
 
#15
real good points on this forum. We use 'black oxide' pins which do show wear. This is a nice feature bc the visual is a clue for lab technicians to check size with a micrometer to verify, if the pin shows substantial wear.
Black oxide, being a conversion coating, adds virtually no thickness, so any wear evinced through use will be negligible, and shouldn't be seen as a reliable trigger for calibration.
 

Mike S.

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#16
A little late to the thread, but this seems risky as it never "closes the loop." A calibration represents a single moment in time, at the start of the interval. In addition to certifying the pin for use during the next interval, the recalibration (or verification) also confirms that the pin remained in tolerance throughout the calibration interval. Thus verifying the previous X months of measurements. If you purchase new instead of reverifying, you're only getting one half of the information.

Most places that I've worked, there was an evaluation that must take place if a gage failed its recalibration. With varying degrees of rigor, the process called for a risk analysis of the characteristics that the gage was used for in case there was any product recall decisions that had to be made (always deemed low risk).

If I just removed a pin set from the cal program and bought another, I wouldn't have evidence to claim that the pin remained in cal for the whole interval. So I would need to analyze past results.
You are correct. But it is easy enough to verify a few of the most-used pins and make it not risky.
 
#17
You are correct. But it is easy enough to verify a few of the most-used pins and make it not risky.
I am in 100% agreement. In fact I've been in places where the metrologist pours a silicone seal over top of the pin after calibration. When the cal interval on the set came up, pins with the seal intact (i.e. not used since the last cal date) were automatically accepted.
 
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