Calibration Frequency of CMM as per ISO/IEC 17025

[dandrewsca]

I have a customer asking if there is any documentation to state that the CMM must be calibrated every year or is 18 month intervals okay. Does anyone have anything in writing from 17025 that says this or is it just an industry accepted standard.
Thanks
Dan

 

[AndyN]

Dan:

There's nothing in ISO/IEC 17025 about such a thing. The selection of a calibration frequency is dependent on a number of issues, one being the stability of the equipment. If a cmm is located in a 'harsh' environment it may not even last 12 months before it needs a check! What's needed is data to help make the decision. Even the 'as new' calibration can give you a clue.

The best advice I've found is to start a schedule of intermediate checks, using an artifact - the ANSI ball bar test is one way - to see what kinds of readings you get. The manufacturer may suggest a yearly calibration, but without the data even that may be too frequent and the cmm may go much longer without a full blown calibration.

 

[John Broomfield]

I have a customer asking if there is any documentation to state that the CMM must be calibrated every year or is 18 month intervals okay. Does anyone have anything in writing from 17025 that says this or is it just an industry accepted standard.
Thanks
Dan

Dan,

I agree with Andy. Your calibration process for each device should show how often you need to calibrate. Do not stick to manufacturer's recommended frequency because they do not know the circumstances of use. For example, is the device used once a month or once an hour? Another example, is the device used in a dusty environment or clean environment?

You may find that you are wasting money on too frequent calibrations or too infrequent verifications.

John

 

[True Position]

Personally, I do not consider adjusting calibration intervals until I have a few years of records showing that it was in spec when it was calibrated. Only then I start considering moving the time back. I have yet to have an auditor have an issue with that.

If you want to check the machine between calibration cycles, I use gage blocks to check all 3 axis and a couple ring gages. Southern Gage also makes an artifact for CMM checking that some people have recommended:
http://www.gsgage.com/content/our_products/surveillance_masters.asp

 

[cbearden]

There is nothing wrong with having an 18 month Calibration Interval....as long as the CMM is giving you accurate results and you can correltate those results using another method, it's your choice on the Calibration Interval.

 

[DCORCOR1]

is there any off the shelf calibration kit for cmm's where I can use it myself rather than getting manufacture in, for cost reduction puposes, our cmm's are very stable but to push out the vendor calibrations I would some fixture that I could use in the interem.

 

[Citizen Kane]

Hi !

You should include your calibration on your maintenance plan. Also, you should perform some regular checks (these are also scheduled) so that you can see in time if you are out of specifications and need a calibration. This is the system that we have installed here in our plant.

 

[AndyN]

is there any off the shelf calibration kit for cmm's where I can use it myself rather than getting manufacture in, for cost reduction purposes, our cmm's are very stable but to push out the vendor calibrations I would some fixture that I could use in the interim.

There are a couple of products made to do quick checks of accuracy. Renishaw has/had a 'Machine Checking Gauge" - it looks like it's a 'QC-10' now.

There is also an ANSI B89 type gauge available for such a check, too. http://cmm.helmel.net/tag/b89-ball-bar-kit/

 

[Krink]

We have very large CMM's at my company and I am charged approx 1K to have them certified to MY spec requirments. If I find an out of spec condition, I then pay 5 to 7 times that because the software to map the zone is proriatory to the CMM manufacturer. These machines are in a clean room and on very good foundations and unless there is a collision, there is very little to cause them to go out. After seeing little change, I have implemented our own calibration yearly and pay the 1K every two years.

 

[Mexicanquality]

Not, the norm doesn´t mentioned nothing about it, even the CMM´ supplier doesn´t know the real period because depends of the use, conditions, etc.
Us ans artifact (certificated) is the best option to know if your machine is measuring good (just be sure that the artifact covers the 3 axis and lenghts neccesaries according you CMM size).
If you have this Chart is a kind of stability studie.

Regards