Pin Gage Sets - Calibration costs - Just buy new ones?

N

Norman V

#1
Here's something that drives me nuts on which I'd like some feedback.

Here are prices for brand new 'ZZ' class pin gauge sets. Each set comes with a certificate of accuracy (so it's calibrated and traceable to a national standard):

50 pc set .011-.060 = $54.00
190 pc set .061-.250 = $118.00
250 pc set .251-.500 = $174.00

Now, here is what it costs to get those same sets of pin gauges calibrated by an outside source when they come due:

Single set calibration $3.50 ea.
50 pc set .011-.060 = $175.00
190 pc set .061-.250 =$665.00
250 pc set .251-.500 =$875.00

Multiple sets calibration $2.50 ea.
50 pc set .011-.060 = $125.00
190 pc set .061-.250 =$475.00
250 pc set .251-.500 =$625.00

I can get a slight discount if I have multiple sets calibrated simultaneously, but still it costs 3 to 4 times more to get the things calibrated than it does to just throw them away and buy new sets! What is wrong with this picture? I understand that one option is to purchase the equipment that will allow me to perform the calibration myself in-house, (0.0002" accuracy), but it is quite expensive, and would itself cost a bundle to be calibrated regularly.

Is anyone else out there struggling with the same issue? What have you done to resolve it?
 
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Jerry Eldred

Forum Moderator
Super Moderator
#2
I don't particularly struggle with that situation as my present employer doesn't have pin gauges at this site.

However, although it may not be a popular answer, I guess I'm going to have to go for it anyway.

If a company buys new, certified pin gages. If those pin gages are important enough to make it into the control plan (or whatever it may be called by the particular company), that means the accuracy of those pin gages is important to product quality or reliability. Therefore it is important to know that they are in tolerance, and if they go out of tolerance, it is important to know that as well. So when an old set of pin gages goes out of spec, it may well be a good idea to just buy a new set.

However (and this is a big however), you also need to know what has happened to those old pin gages so you can make a good decision as to potential discrepant material disposition. If you discard the old set, and just buy a new set without having the end of life accuracy of the pin gages checked, you lose the ability to know if and/or when any of them went out of tolerance. If there are safety issues or product liability issues associated with the parameter tested using the pin gages, the calibration cost is much less than the alternative if bad product has made it out the door undetected as a result of out-of-tolerance pin gages (unbeknownst to the user).

It is painful to spend money anywhere you don't need to, and even some places you do need to; especially in these economically tight times. However, when it comes to calibration, I find I often have to fight the "red-haired stepchild" syndrome calibration often has to fight. There is the common view that calibration is something you do to fulfill a paper requirement. So companies constantly struggle with why they have to calibrate. Pin gages, along with so many other things are no exception.

I have seen many companies calibrate anything with a meter movement or display or moving parts (figuratively) because they aren't certain as to whether items require it. Because smaller companies normally don't have metrology experts in-house, there is the ongoing struggle as to when to calibrate or not calibrate.

The vast oversimplification of how to deal with this struggle is to ask the philosophical questions:

1. Do I care if the measurement is right or wrong?

2. If the measurement is wrong, is there any possibility that product will not meet specs or create any safety or reliability hazard?

If the answer is yes to either of the above, then the item needs to be calibrated. I know I probably gave somewhat a tongue-twister answer this morning (haven't had my second cup of coffee yet). But hopefully, I have given some sort of insight.

------------------
 

Marc

Hunkered Down for the Duration
Staff member
Admin
#3
Thanks for the response, Jerry! It is very complete and thoughtful. Your help is appreciated by us all, as always!

-> What is wrong with this picture?

Nothing at all. The manufacturer has everything there to check pins as they're produced. For an outside lab to verify pin gages (as we know, you cannot 'adjust' them and, right or wrong, the word adjustment is often associated with the word calibration) at a later date is a much different, and often more expensive, process. If you want to boggle you mind just a bit, consider calibration of glass ware (volume) and items like glass bulb thermometers.

[This message has been edited by Marc Smith (edited 18 July 2001).]
 
D

DICKIE

#4
We use gage pin sets all the time but not for final inspection unless they are calibrated. The sets are marked referance only and that satisfies our auditor.

Greg
 
N

Norman V

#5
Thanks for your feedback everyone.... Don't get me wrong - I certainly beleive in the necessity of calibration, and I beleive it is worth paying for. What kills me is that it costs more to calibrate them than it does to throw them out and buy new ones.

I work for a company that is considered a recycler - I hate throwing things away when there is nothing wrong with them!
 

Jerry Eldred

Forum Moderator
Super Moderator
#6
I speak as one who is not an expert specifically in pin gages. But one of the challenges it seems to me that occurs with them is that in comparison to other dimensional measurement tools/instruments, they are inherently less forgiving/versatile.

Gage Blocks- you can chart a changed value
Calipers/Micrometers - you can adjust back into tolerance

Pin gages- when they wear past their tolerance limit they are useless.

So it seems they are a unique case.

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R

Ryan Wilde

#7
I feel a need to leap into this one. Norman, you need to check the 'certificate of accuracy' that comes with the pins. They are not calibrated individually, and after actually calibrating literally over 10,000 pins, I have found approximately 10-25% to be out of tolerance (varies by manufacturer). I have even seen a fair number of pins mismarked for size (marked 0.250, actual size 0.252). If you check the catalog very closely, you will see extremely fine print that says something to the effect of 'traceable certificate of calibration $3.00 per pin - new only'.

If you were to actually visit the manufacturer (quality varies greatly), you would most likely be shocked. One of the more well-known manufacturers that I visited was checking 1 out of 10 pins, and that check was at room temperature, the standard was another pin of 'known size', and the measurement gage was a micrometer with a resolution of 0.0001". An impromptu uncertainty calculation told me that the uncertainty of that check was 0.0003", 1.5 times the tolerance of the gage. Needless to say, every pin we bought was checked at 20°C with a gage with an absolute accuracy of 20µin, which still gives an uncertainty of 33µin, barely a 4:1 ratio.

The certificate that you receive with the cost of the pin is that it met their quality control plan, nothing more. Manufacturing expects a certain percentage of what they make to not meet specifications as you well know - but in the field of calibration, it is not expected because each gage can affect thousands of parts and the risk is far too great.

Look at the certificate of accuracy:
- Does it state traceability? (standard used, etc.)
-Does it state the date of calibration?
-Does it state uncertainty?
-Does it make any reference to any specific pin in your set, or even the set serial number?

When you send your pins in for calibration, you get (more than likely) four to six points on the pin checked against standards of known value, and the lab provides you with traceability which can be linked back to NIST (in the US).

Don't be fooled, these are apples and oranges you are comparing.

Ryan

[This message has been edited by Ryan Wilde (edited 18 July 2001).]
 
D

Dave Stauffer

#8
You have received some realy good advice thus far.
Let me interject a few thoughts.
1st, buying new sets of gages and disgarding the old sets- you lose TRACEABILITY. If you go this route, tag the old sets with all calibration history records and archive them.
2nd- buying new pin gage sets, you receive a certificate of conformance. This does NOT give calibration data that can be used to develope history and traceability for your product.
Solution- IF you have a contolled environment in which you can perform in-house calibrations, you could get by purchasing a bench mic for under 5K that is capable of resolution and stated accuracies of .00002" and a grade 1 gage block set with which to do the direct comparisons of size for maybe 2K. Thats a whole lot cheaper than going for the Super-Mic and you can do plug gages an other applications as well. Something to think about. Payback generally is 2-3 years depending on frequency of calibration.

------------------
Dave Stauffer
 
A

Al Dyer

#9
Let's keep this up, and maybe on to other types of gages.

Although not acceptable, a previous company used to use the older gage blocks to prop up machines! Of course they bought the cheap ones from China!

I left the company and am sure they got regular shims and replaced the original gage block set.

Oh well, life is tough and we move with the punches. Always remember, integrity rules!!!

ASD...


[This message has been edited by Al Dyer (edited 18 July 2001).]
 
N

Norman V

#10
Originally posted by Ryan Wilde:
The certificate that you receive with the cost of the pin is that it met their quality control plan, nothing more.

Aha! Very good information. Thanks Ryan, it sounds like you are indeed the expert opinion I was looking for.

This seems to present a new problem. Up until now, I have used this "certificate of accuracy" as the original document to show traceabilty to a known standard. It looks like I'm going to have to request indivindual calibration certs for each pin from now on at the time of purchase...
 
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