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  Measurement, Test and Calibration
  Calibration or not ?

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Author Topic:   Calibration or not ?
Martine
Lurker (<10 Posts)

Posts: 2
From:Belgium
Registered: Aug 2000

posted 30 August 2000 04:53 AM     Click Here to See the Profile for Martine     Edit/Delete Message   Reply w/Quote
The company I work for is a machine building plant that has its own research and development, engineering and design, as well as workshops for the production of machinery, which are all used in the fastener manufacturing industry.

At the moment there is a discussing about which measuring instruments ought to be calibrated and which not.
The head of our assembly department states that the instruments used in his department are only used to ăcompareä two parts with each other (to see if they fit), and therefore should not be calibrated.
On the other hand, the instruments used in our workshop (we also produce our own parts) are used to check the dimensions of a part in production against the one mentioned on its drawing. So, these instruments should definitely be calibrated.
Could you please give me your opinion ?

Also, would it be profitable to do the calibrations in-house ?
Can anyone give an estimate of the costs involved (we have approximately 1500 instruments in use) ?

Thank you in advance.

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Jerry Eldred
Forum Wizard

Posts: 136
From:
Registered: Dec 1999

posted 30 August 2000 10:24 AM     Click Here to See the Profile for Jerry Eldred   Click Here to Email Jerry Eldred     Edit/Delete Message   Reply w/Quote
I think a good, very simple definition of when to calibrate is if you care whether the instrument is correct. If you don't care whether the instrument is correct, then you MAY not need to calibrate. If this is a QS9000 plant, there are another more complicated set of answers. Please tell me if you are QS9000 or ISO9000 and we can address that question separately.

As for the cost to calibrate, that is a complicated question. If you only have calipers and micrometers, you may find it is not too costly. But if you have many different types of instruments, you will have to do a cost evaluation. There are a number of factors to be considered. You will need a properly trained person to do the calibrations. You will need a written policy and written procedures. You will need proper equipment to do the calibrations, and need to maintain proper externally done calibrations on all of those. If your instruments are pretty simple, all of the above is probably pretty simple, and not too costly. If you have many highly accurate instruments that measure many different types of parameters, it may be questionable as to whether you choose to calibrate in-house. If you can post a set of how many, and what type instruments you have, I can give you a little better idea as to whether or not to calibrate.

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Jim Biz
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Posts: 275
From:ILLINOIS
Registered: Mar 2000

posted 30 August 2000 03:12 PM     Click Here to See the Profile for Jim Biz   Click Here to Email Jim Biz     Edit/Delete Message   Reply w/Quote
We support the view that "Fit-up gages" (such as matching assembly parts) - should be handeled as - for reference fitup only - BUT we included clarification statments in our doc's allowing this to be done - by authority of our qualified head inspector... and included a work instruction on how to evaluate - fit-up gaging prior to each use.

TECHNICALLY they aren't "CALIBRATED" to a standard - identified - entered into the report history records - but each are evaluated and verified to our internally set tolerance ranges prior to being used.

All other gaging insturments that are used "to qualify products are part of the calibration system".

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Bill Ray
unregistered
posted 03 September 2000 07:13 PM           Edit/Delete Message   Reply w/Quote
Calibration can be a reasonable insurance at a reasonable cost. The overall cost to calibrate 1500 instruments, assuming general inspection calipers, micrometers, torque, pressure, gage blocks, pin sets, etc. should be about $15,000 US$. However, if you do not have the calibration equipment, the most economical way is to subcontract to a general calibration service. Otherwise, you will have the supermicrometer cost, the cost of developing procedures, and the cost of calibration equipment maintenance and calibration.

Reasonabl insurance, if done in the most efficient manner. Costly, if not.

Bill Ray

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louie
Forum Contributor

Posts: 19
From:Rochester Hills, MI
Registered: Feb 2000

posted 06 September 2000 08:52 AM     Click Here to See the Profile for louie     Edit/Delete Message   Reply w/Quote
Jerry,(and anybody else !)

We are seeking T&E Certification and would like your interpretation on our requirements for calibration.

Presently we are tagging / id'ing all employee owned tooling as "reference only" and only calibrating company owned tooling. We are trying to establish intervals for calibrating tooling.

Presently I have no way of knowing when / where any tool is used as there is no traceability to any prints / machines that we build to any tooling used to verify measurements, other than my CMM machines.

I think this is too loose - your thoughts?

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Martine
Lurker (<10 Posts)

Posts: 2
From:Belgium
Registered: Aug 2000

posted 06 September 2000 09:54 AM     Click Here to See the Profile for Martine     Edit/Delete Message   Reply w/Quote
Jerry, Jim, Bill,
Thanks for your quick responses.

Jerry, to answer your first question, the company is ISO9001.
As for the different types of instruments, I will try to give you an estimate of what we have:
+/- 100 clock gages (external, internal, depth), +/- 500 micrometers (of all sorts: inside, outside, depth, 2-points, 3-points, digital, with build-in clock gage, blade, thickness, screw thread, tubular inside, disc), +/- 350 calipers (of all sorts: analog, digital, inside, depth), 2 surface plates, 41 pocket test indicators, +/- 20 gage block sets, 15 height gages, 25 graphometers, 12 torque wrenches, and some other instruments of which I donât know the proper translation.

Two years ago, we send away a part of our instruments to a general calibration service. Using the cost of this calibration as a basis, we estimate the overall cost to calibrate all of our instruments at about $33,000 US.
Since we do not have any calibration equipment, or the personnel to do the calibrations, we wonder if it would be worth trying in-house calibration.

Any response still greatly appreciated.

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Jerry Eldred
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Posts: 136
From:
Registered: Dec 1999

posted 07 September 2000 08:39 PM     Click Here to See the Profile for Jerry Eldred   Click Here to Email Jerry Eldred     Edit/Delete Message   Reply w/Quote
Martine - I will have to apologize that I am on vacation in COOL green Vermont until next Monday. I WILL give you an answer. I have a slow connection from a house up in the mountains, so I have to restrict myself to brief answers. I don't think I will do you justice until I am back in the office next week. Briefly though, it looks as though you have a mixed bag. A lot of what you have looks as though it very well be worth your while to calibrate in house (calipers and micrometers most certainly). The others, let me tackle next week in better detail.

Louie - Yes, I agree that is too loose. There should be little differentiation between company owned and personally owned measuring instruments. If they can easily be interchangably used, it is dangerous territory to leave one uncal'd and the other cal'd/. As above with Martine, more detail next week.

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Marc Smith
Cheech Wizard

Posts: 4119
From:West Chester, OH, USA
Registered:

posted 08 September 2000 09:05 AM     Click Here to See the Profile for Marc Smith   Click Here to Email Marc Smith     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by louie:

We are trying to establish intervals for calibrating tooling.

Presently I have no way of knowing when / where any tool is used as there is no traceability to any prints / machines that we build to any tooling used to verify measurements, other than my CMM machines.


Do you have any past calibration data? Take a look through and see how the cals went. Was the tool in cal? How much adjustment was made (if any)? Etc. You can use past data to justify intervals.

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