Ring Gage Calibration Sizes Shrunk with New External Vendor (supplier)

Z

z28tt

#1
Hi guys,

Hopefully this is the correct forum... We generally use ring gauges (gages?) to set the dial bore & Mueller gauges on the shop floor, and sometimes in QC. The last few calibration cycles noticed minimal wear, so the cal interval was extended based on past experience. This time around, the external calibration vendor was changed, and our new certs have a huge difference (usually 50-100 millionths change). Some ring gauges grew, others shrunk, and many no longer fit into the Class XX or X originally stamped on the ring.

If the gauge moved into one class lower, I was planning on surface grinding the old class off, and laser marking the new one, along with cal date (we had issues w/ stickers falling off, and it was easier to laser mark a new date, then re-train operators to notice cal stickers had fallen off!). If we just changed classes, many would be in Y and Z (from XX or X originally).

The problem is that some gauges were Go/Nogo's, and the way the gauge "moved" was in the 0 direction (Go=+0, -tol), so it'd have to get changed to a NoGo or a Master.

What I'm trying to figure out is how to handle it w/ the external calibration houses. Both were certified to various standards (ISO 17025, Mil 45662A, Z540, etc...). Uncertainty on the cert is 10 millionths for the new house, and 5 millionths for the old one. I don't know why we switched...

Any guidance on how you guys would handle this? I'm thinking of sending some of our ring gauges with the biggest discrepancy back to the 1st cal house to see what they come up with...
 
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bobdoering

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#2
Re: Ring Gage Cal Sizes Shrunk with New Ext Vendor...

Ouch! I would be tempted send a sample of the worst cases to another cal lab to see which of the other two was right. Best out of three...:cool:
 

Jen Kirley

Quality and Auditing Expert
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#3
Re: Ring Gage Cal Sizes Shrunk with New Ext Vendor...

I agree - I would seek a second opinion, and if it is far different than this last one, I would suspect some error in the calibration process there, and take the issue up with them. I would not rescribe these gages until I had done this followup.
 
J

jfgunn

#4
Re: Ring Gage Cal Sizes Shrunk with New Ext Vendor...

I agree with others that sending the rings to another lab would be a great idea.

I might suggest the following as well:

1.) Look into claimed calibration uncertainties from these two labs. To be honest 5 microinches seems a little low. I realize that the discrepancy is much larger than the uncertainties, but I would still look at them a little closer. Ask them what they have included in their uncertainty budgets.

2.) Look into accrediteation. You mentined ISO 17025, Mil STD 45662A, and Ansi Z540. The only one I would really consider is ISO 17025. Make sure the cert says Accredted to ISO 17025, not some "compliant to...." The 45662A kind of worries me since this standard was obsoleted years ago. It sounds to me like you may have one of the many labs who just put an alphabet soup on their certs. Maybe not.

3.) Look into the procedure that each lab used. Did they measure the rings in the same spot? Did they take measurements too close to the chamfer if the rings have a chamfer? Do they perform the calibration in a nice temperature controlled lab? etc...
 
Z

z28tt

#5
Re: Ring Gage Cal Sizes Shrunk with New Ext Vendor...

I'm taking 5 of the oddest certs, and sending them out for a third opinion today. The alphabet soup of accredidations in my last post is that some were of them were from certs going back a few cal cycles to '01 and '03, as well as our boilerplate on the back of the PO... I'll make sure the cert house is accredited to 17025, latest rev. Once I get the results back, I'll ask the last (odd reading) lab for their cal procedures & equipment, and try to figure out what happened. Will let you guys know in a week or two.

Thanks!
 
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S

Southern Girl

#6
Re: Ring Gage Cal Sizes Shrunk with New Ext Vendor...

Please don't get the manufacturer's tolerances (X, XX, etc) confused with the acceptable limits you will use for calibration. Those tolerances are for "new" gages only. Once you have used them the changes in the surface finish alone will result in a difference of several millionths. If you are only using them to set other gages, all you need is to know what they really measure. You may have to re-etch the size on the ring, but other than that, it would still be usable. Of course you would have to establish your ring size tolerance based on your feature (being measured) tolerance to prevent accepting non-conforming product, but you can keep that simple as well.

This does not excuse the variations in calibration results that you received. I have experienced the same situation from both sides: the customer and the vendor. You should send at least one or two of the questionable gages back to the new vendor and tell them why you are returning them. Also, they should not charge you for the re-check no matter what the new results are. That is the least they can do if they want to keep your business.

:applause: Good luck and :agree1: kudos to you for watching those calibration numbers. Too many times the calibration certifcate is just filed away without a glance.
 
Z

z28tt

#7
Re: Ring Gage Cal Sizes Shrunk with New Ext Vendor...

If you are only using them to set other gages, all you need is to know what they really measure. You may have to re-etch the size on the ring, but other than that, it would still be usable.
That's something I'm considering. We're already laser engraving the "due by date", so it's no big deal to engrave a new size (as long as it's consistant). They're all getting used to cal dial bore gauges, so as long as the operator knows what size the ring is, we're good. I just wasn't ready to re-mark 50 rings based on funny readings on the last batch of certs...

This does not excuse the variations in calibration results that you received. I have experienced the same situation from both sides: the customer and the vendor. You should send at least one or two of the questionable gages back to the new vendor and tell them why you are returning them. Also, they should not charge you for the re-check no matter what the new results are. That is the least they can do if they want to keep your business.
Thanks. I'll do that as well. The 5 gauges sent out last week for a third opinion should be coming back. It all adds up when you've got 80+ gauges at $25-$35ea...

:applause: Good luck and :agree1: kudos to you for watching those calibration numbers. Too many times the calibration certifcate is just filed away without a glance.
Thanks! I just got re-hired at my last company (aerospace job shop) a few weeks ago as the QC Manager. I've got 3 inspectors, and about 20 guys on the shop floor feeding parts through QC, as well as ISO/AS9100 accreditations, etc... It's been a pretty steep learning curve (my background is engineering), but I'm getting a good handle on things. With the amount of responsibilities, the days definitely go by quickly!
 
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J

JAltmann

#8
I agree with the others that the 50-100 microinch difference is huge, but i must ask when did you start surface grinding these gages? Was it after the last calibration? Althought i don't think this would cause a huge difference the grinding may be a cause the gages changing size.

As they get heated up un-evenly and allowed to re-cool this will alter the material.

Did each of these labs give results at 3 levels 90 degrees apart?
 
Z

z28tt

#9
I agree with the others that the 50-100 microinch difference is huge, but i must ask when did you start surface grinding these gages? Was it after the last calibration? Althought i don't think this would cause a huge difference the grinding may be a cause the gages changing size.

As they get heated up un-evenly and allowed to re-cool this will alter the material.

Did each of these labs give results at 3 levels 90 degrees apart?
The rings began getting laser engraved last cal cycle, when we realized the guys in honing couldn't figure out that they need to replace cal stickers when they fall off after an oil bath, and some int'l audit CA's on gages w/o cal stickers. Only 1 side was skimmed. In any case, our grinding guy is great, and did a super light skim off the top, just enough to get the laser mark off. This is w/ coolant as well, and no major heat into the part. Rings didn't even get warm to the touch. The readings were 3 levels 90 apart for all three certs, so if the top was skimmed, the middle and bottom readings should still be somewhat consistent, even if the slight vibration "relaxed" the material. That being said, I'd figure any change due to the grinding would be consistent (larger or smaller).

ANYWAYS... :)

I received the results of the 5 rings I sent in (deviation in millionths):
Size - Old Cal - Aug08 Cal - Dec08 Cal
.1245 XX Go, -05, +75, +47 to +55
.1870 X Master, +20 to 30, -40, -11 to -17
.4342 X NoGo, 0, -40, +26 to +38
1.2050 X Master, +10 to +20, -54, -49 to -52
2.000 X Master, +15, +73, +2 to +10

At least one of the five is close!

Reading the cert, this time it was done on a P&W Labmaster HQC-224, calibrade daily, at 68 deg and 45%. Lab is ISO 17025 accredited, and cert is in compliance to ISO-10012 and Z540-1 (per our old PO verbage...). Uncertainty is (14+5L)uin and coverage factor = k2 at 95% confidence.

So now I've got 5 gages with certs from three cal houses and 3 very different readings, with 80 more gages that I don't know what to do with. At this point it seems like I could calibrate them myself by tossing a dart at the wall. :p
 
J

JAltmann

#10
How are these gages used on a daily basis? What is the surface finish like on these gages?

Those numbers are odd for a ring gage (alot more variation than i am used to seeing), but if the ID has alot of wear and the surface finish is no longer a lapped finish i might believe it.
 
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