Calibration Frequency for Rarely Used Gages

Wes Bucey

Prophet of Profit
Everyone:
Help me understand what you mean by "calibrate" as opposed to "certify" or "zero out" and also how you relate any of these terms to Gage R & R (MSA)

As I read posts here and in ASQ's Forums, there seems to be a lot of interchangeability of terms far different from my understanding and experience over the last 25 years.

I have hundreds of horror stories about operator-owned personal micrometers which have never, ever been included in organization calibration or certification processes. (Also scary stories about organization-owned instruments.) One guy used his two-inch micrometer to "gently" crack walnuts so the meat wouldn't shatter. Other guys used to crank the micrometer down so hard the anvils left dents in the material (mechanical advantage of a screw is amazing!)
 

CarolX

Trusted Information Resource
Wes Bucey said:
Everyone:
Help me understand what you mean by "calibrate" as opposed to "certify" or "zero out" and also how you relate any of these terms to Gage R & R (MSA)
Wes,
You are correct....and for as long as I have been in the quality field..the term "calibrate" has actually meant "to check". Calibration is the adjustment you make for an out of tolerance condition. But to make things as easy as possible in the worlds we work in...I think we all refer to the function as "Calibration".
Right or wrong....IMHO it is just semantics. As long as the message is understood.

CarolX
 
R

Rob Nix

If that is the case, then last week I calibrated my engine oil, I calibrated my blood pressure, and I even calibrated the caliber of my calipers.

Seriously though, if the AIAG is still a credible authority, it defines calibration in its Measurement Systems Analysis (MSA) manual as "comparison to acceptable standards", and in QS-9000 as "a set of operations which compare values taken... to a known standard". So, indeed, "checking" is a valid synonym. Although I too tend to think of calibration as the act of bringing a device back to nominal.
 

Charles Harvey

Inactive Registered Visitor
One method we have used for seldom used gages is to use different interval types. We use the standard "flat" time where a gage is due 91 days after the calibration date, the normal interval type. We also use "issue" time where calibration time only counts when gages are in use. If they are sitting in a drawer in the tool crib, the time isn't counting. We also have the capability of counting every use of a gage.
We currently have a computer system to track calibrations, but years ago we did the same thing with cards.
 
C

CINDY

Bob,

Can't you rotate your gages and put them on rotating calibration cycles?

In our testing lab, we state that items requiring calibration that are seldon used, are taged and placed in the equipment cabinet and calibrated prior to use. For us, calibration is much more expensive ($500).

On the same note, out side of the test lab, we do our own calibrations including company and employee owned. Only our master gages are sent out for calibration.

Is it worth your efforts to purchase the necessary equipment to perform calibrations yourself?

Cindy
 

CarolX

Trusted Information Resource
Charles Harvey said:
One method we have used for seldom used gages is to use different interval types. We use the standard "flat" time where a gage is due 91 days after the calibration date, the normal interval type. We also use "issue" time where calibration time only counts when gages are in use. If they are sitting in a drawer in the tool crib, the time isn't counting. We also have the capability of counting every use of a gage.
We currently have a computer system to track calibrations, but years ago we did the same thing with cards.
Hi Charles and Welcome to the Cove:bigwave:

What a great idea. How difficult was it to manage in the card system?

CarolX
 

Charles Harvey

Inactive Registered Visitor
It was not difficult to manage in the card system. It just took a a little extra work. The cards were like the old library cards, we used 4 x 6 index cards. The crib attendant would write on the card were the gage was being issued to and the date, and when it was returned they would manually subtract the days it was out and mark a running balance on the card. When the balance got within 10 days the gage was issued to calibration.
 
G

Grizz1345

If I were in your position I would look at a calibration cycle based on usage. This is an accepted criteria for setting a cycle time. In doing this you might find that the seldom used gages only need calibration once every 2-3 years.
 
K

Ken K

Why don't you consider extending the outside calibration interval on your seldom used gages and verify them internally between calibrations?

You could perform those, say, every three or four months. That way you would know the gages are still in tolerance during storage and are ready to go when needed.

What would you do if you extended the outside calibration intervals to 18 months and during the 17th month you needed to use the gage only to find the batteries are dead (if used) or the gage is unusable?

Not an ideal situation...
 

Wes Bucey

Prophet of Profit
Golly, Ken. I guess the rest of us don't think of batteries when we think of calibration. A change of batteries doesn't change calibration of any dimension measuring instrument. A weak battery might make a big difference in items like continuity testers, voltage meters, and the like. I expect most organizations deal with "expendables" like batteries in one of two ways:
1) keep spares handy for instruments which use them and replace as necessary
or
2) deal with them like major office buildings deal with ceiling lamps to save labor costs because the labor cost is more than the cost of the expendable product - replace ALL on a schedule which is shorter time period than useful life of the product (you still have to keep some spares on hand for "lemons" and extraordinary usage, though).

It occurs to me to elaborate on labor cost:
A trip to a tool crib for a $20/hour technician to get a replacement battery is usually more costly than the cost of the battery, so many organizations have tool crib attendant include a fresh spare battery when issuing a battery-operated tool or instrument. In an inspection lab setting, spare batteries ought to be easily accessible and training in use of an instrument should include method of replacing battery.
 
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