What is the best procedure for calibrating / certifying our Calipers?

We primarily use calipers for inspection. We have a set of gage blocks certified to NIST. What is the procedure for certifying our Calipers. We are going for ISO9002 in 98 and QS9000 in 99. I know we have a lot to learn in this area. Is anyone willing to help us get started down the right track.
thanks.

[Marc]

You have two choices for your calipers:

1. Send them out for calibration.

2. Work up a procedure for calibation and use your gage blocks to verify the calibration of the calipers.

How's that for starters?

And to add .. if you use the 2nd method (recommended .. thats what we do) make sure you have a procedure to regularly send out the gage blocks for calibration to NIST.

ALSO MAKE SURE YOU HAVE A CYLINDRICAL RING GAUGE AND ENOUGH BLOCKS TO CHECK THE COMPLETE RANGE OF ANY CALIPERS YOU HAVE(ie. 12",6", etc.)

[Marc]

Or at least the ranges or points you use.

[sarasheed]

We are using Stick Type of Michrometers to measure the Internal Diameters from 50 mm to 1500mm.This michrometer consists of a Michrometer Head and set extension rods which if assembled will read upto 1500 mm.I want to know how to calibrate this type of Michrometer.At preselnt we calibrate the Michrometer Head for the Pitch deviation and and attach the reading of each individual extensiln Rod in the calibration certificate .This Certificate is will be there along with the Michrometer during its use.

I request somebody to react to this method.Is it serving the purpose of calibration?.Can somebody suggest any other method.

[Hershal]

The basic approach seems OK, although I would point out that you also need to take into account what is known as "wringing", that is the joining of gage blocks - or in this case rods - to obtain a given length. The normal value given to ringing is 0.00005 inch per wringing. Thus, joining five rods will have four junctions, or wringings, with a total number of 0.0002 inch.this goes into the uncertainty calculations also.

There are likely some other sources of error you should take into account, but aside from temperature and RH it would be difficult to say which, without knowing the specific situation.

Hope that helps.

Hershal

Moderator's comment:
"Wringing" is the action of putting two blocks or rods together and giving a slight twist to "wring" the air out from between the blocks and form a vacuum which helps hold the blocks together from the outside air pressure pushing the blocks together. In some cases, the block can be suspended upside down and will not separate. To disengage the blocks, they are "unwrung." -Wes Bucey

[sarasheed]

Thanking you for giving reply to my doubt about calibration of Stick type Inside Michrometers.

S.A.Rasheed