Electric 0-8" Caliper Calibration Tolerance Question.

B

Bob_M

#1
Quck Electric 0-8" Caliper Calibration Tolerance Question.

Quick Question/Answer I hope.

In-House Calibration/Verification of an Electronic 0-8" caliper with .0005" resolution. (Recently dropped but only a minor issue).

OK If the resolution is .0005" can readings technically be off by .0005" and still be considered "in-spec"?

Specific Details from today's post-dropping verifcation:
.1000 = .0995
.1005 = .1000
.2000 = .1995
.3000 = .2995
.4000 = .3995
.5000 = .4995
Did not "ring" any between these yet...
1.0000 = 1.0000
2.0000 = 2.0000
3.0000 = 3.0000
4.0000 = 4.0000
5.0000 = 5.0000 (rung 1 + 4)

Production parts only use 3 decimal places and usually are no lower than +/- .005 (Most are +/- .010 and historically at the median and/or very static parts - metal stamping).

Is this gage still good to use for OUR application?
Would it be good in other applications?

Overall gage is still in good shape, but it is a ? years old and used within prodution (at most 10 times a day typically).
 
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B

Bob_M

#2
Anyone?
I could use some opinions ASAP. I need to return the gage to production if possible. (It was dropped).
 
J

Jimmy Olson

#3
Generally speaking if the resolution is 0.0005 then the spec for the caliber is +/- 0.001.

If your readings are off by 0.0005 that's perfectly acceptable, especially if that is tighter than the tolerances you're measuring.

Hope that helps :bigwave:
 

Mike S.

Happy to be Alive
Trusted Information Resource
#4
I agree with Richard. Those readings are as good as I would expect from a new caliper. We use the same type caliper (mostly electronic Mitutoyuo's) and my internal spec. for cal. is if it reads within .001" it is good to go, though it is usually withion .0005". Then, I only use calipers for tolerances of +/- .003" or more. At the tolerances you quote you should be good to go. One thing to watch is the wear on the thin portions of the OD measuring part and the ID measuring part -- they wear faster than the thick portion of the jaws and this can be a problem sometimes.
 
B

Bob_M

#5
Thanks for the help and comments.
I thought our internal work instruction didn't quite look right... Time for another revision :)

I'm not quite sure what to do when the gage's get excessively worn. Purchase request for new ones will probably be OK'ed but then we're left with "partially" good gages that can't be used in most applications... :(
 

Mike S.

Happy to be Alive
Trusted Information Resource
#6
Sometimes if I have calipers that are off by > .001" (say, .0015" - .003") I will stick an "uncalibrated reference only" sticker on them and use them in non-critical areas where they get rough use anyway. For example, if the guy in the stockroom just needs to know within .010" if the size of stock is big enough to issue for a certain job he can use uncalibrated "ballpark" calipers with no harm done. Even if he were way off, the worst that would happen is the mfg. dept. would take the undersized stock back to the inventory guy and say the stuff is too small, and this would tell the inventory guy he screwed-up or that his calipers are ready for the trash.

Or, if, say the ID jaws are worn but the OD jaws are fine, make the ID jaws unusable, give it a limited calibration, and use it for OD measurement applications only. No harm in that.
 
B

Bob_M

#7
Mike S. said:
Sometimes if I have calipers that are off by > .001" (say, .0015" - .003") I will stick an "uncalibrated reference only" sticker on them and use them in non-critical areas where they get rough use anyway. For example, if the guy in the stockroom just needs to know within .010" if the size of stock is big enough to issue for a certain job he can use uncalibrated "ballpark" calipers with no harm done. Even if he were way off, the worst that would happen is the mfg. dept. would take the undersized stock back to the inventory guy and say the stuff is too small, and this would tell the inventory guy he screwed-up or that his calipers are ready for the trash.

Or, if, say the ID jaws are worn but the OD jaws are fine, make the ID jaws unusable, give it a limited calibration, and use it for OD measurement applications only. No harm in that.
That seems to work for you...
BUT we need ID and OD readings on most of our parts that use a caliper, and "good-enough" is not how we currently measure in-coming material. (No Offense). Its either good or not good. "Good-Enough" only works if our internal requirements happen to be tighther than an drawing and there was some slight variance that In-coming did not measure... Then we can deviate/OK as needed. *shrug*

I took that last QA mgr a while to get ISO and quality requirements into some production people's daily routinue and thought process. I can't start removing to many quality items without loosing personal and system respect from the shop. => Uncalibrated gage might as well be in the garbage in our shop!
 

Mike S.

Happy to be Alive
Trusted Information Resource
#8
"I can't start removing to many quality items without loosing personal and system respect from the shop. => Uncalibrated gage might as well be in the garbage in our shop!"
_____________________

Then by all means garbage-can the out-of-cal items. A $150 set of calipers is not worth the potential damage it could do your company.
 
B

Bob_M

#9
Mike S. said:
"I can't start removing to many quality items without loosing personal and system respect from the shop. => Uncalibrated gage might as well be in the garbage in our shop!"
_____________________

Then by all means garbage-can the out-of-cal items. A $150 set of calipers is not worth the potential damage it could do your company.
I will once they are out of spec ;)
But at the moment the one I described above is not YET...

I would be nice to use "reference" calipers, but at our shop we have no real use for them. *shrug*
 
R

Ryan Wilde

#10
I' d have gotten to this sooner, but I've been living out of a suitcase for the last 2 weeks (still am, but I grabbed a laptop for this leg).

Okay, I'm partially running from memory, but resolution and specification are entirely different. For example, Mitutoyo specs their digital calipers with 0.0005" resolution to:

0-8" ± 0.001" ± 1 count quantizing error ( basically ± 0.0015") @20°C
>8-12" ± 0.0015" ± 1 count quantizing error ( basically ± 0.002") @20°C
>12-24" ± 0.002" ± 1 count quantizing error ( basically ± 0.0025") @20°C

Military specs are (here's the memory part)

0-6" ± 0.001"
>6-24" ± 0.002"

Hope this helps,

Ryan
 
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