Caliper Calibration Instruction - Example Caliper Calibration Procedure Wanted

janah214

Inactive Registered Visitor
#1
I do not have much experience with internal calibration. Could someone please send me a sample of an instruction for caliper calibration that includes tolerance?

Thanks
 

Hershal

Metrologist-Auditor
Staff member
Super Moderator
#3
Welcome to the cove.

I posted a reply to your question in the ISO9001 list, and repeated here. Hope it helps.

The best work I can recommend is The Metrology Handbook, published by ASQ Press. It is for Metrology (aka calibration, the science of measurement) what the Juran reference work is for quality.

As for documentation, you need to keep the information on the gage blocks you use, along with the certificate number from the gage block's last calibration, and next due date. That provides the traceability information above your organization. You should become familiar with measurement uncertainty so that you know the errors involved with your calibration.

As for instructions, if you are going to do much calibration, join GIDEP www.gidep.org I think is the website, and you can access military (e.g. USN's NA 17-20 series) which are considered validated.

Another thought, if you do a lot of internal cal, is to consider seeking accreditation down the road for your internal lab. The accreditation is to ISO/IEC 17025. There are five accrediting bodies in the U.S. that are accepted currently, so talk to all, if that is an option for you.

Also, get a subscription to Cal Lab Magazine, the leading periodical in Metrology. www.callabmag.com

Hope this helps.

Hershal
 

Marc

Retired Old Goat
Staff member
Administrator
#4
The basics:
Both the inside jaws and the outside jaws need to be calibrated, as well as the depth rod and the step measurement, if these are used. Calipers should be frequently checked for accuracy. They are more susceptible to damage than other tools.

To check for wear in the jaws, do this: clean them and close them. Then hold them up to the light and if they're worn you'll see light shining through the gaps. You can continue to use the calipers if you measure with the unworn surfaces. For total reliability, however, you'll have to send the calipers for servicing. The surfaces can be ground flat again.

For the outside jaws it's a simple matter of inserting a series of gage blocks between them and recording the caliper readings. They must not deviate by more than one graduation (.001") over the first 4" of range. From 4" to 8" the error may be .0015" (one and one-half graduation). From 8" to 12" the error can be .002". Accuracy may vary among different models and the manufacturer's specs should be consulted for this information. Take readings at 1-inch intervals. Three gage blocks (see below) of 1", 2" and 3" sizes will be all you need.

To calibrate the inside jaws you may use a set of ring gages. Do not rely on very small ring gages because the inside jaws can not accurately measure small inside diameters. You may also set a calibrated .0001" micrometer to 1" (and higher, if possible) and then use the inside jaws to measure this distance. Since the micrometer has a discrimination ten times that of the calipers, you'll get an accurate reading.

Repeatability means the dial hand returns to the same position on different attempts to measure the same gage block. If this fails, then you'll have to have the calipers serviced.
 
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