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Micrometer Calibration Procedure - Please critique


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  Post Number #1  
Old 23rd May 2006, 06:20 AM
apestate's Avatar
apestate

 
 
Total Posts: 518
Thank You! Micrometer Calibration Procedure - Please critique

Hello forum

This procedure has some logical problems, but aside from the mistakes of writing quickly, I was hoping someone would be interested in generally critiquing 1.) style 2.) technical content

The calibration procedure isn't written for accredited calibration services or ISO 17025--it would simply be used in an ISO 9001:2000 category job shop.

How do you feel about the content? Measurement uncertainty has been left out entirely. Anything involving torque of measurements has been left out, leaving that up to the operator. Gage block wringing and stacking has also been left out. I haven't included anything about optical flats, and I made attribute judgements out of spindle play, perpendicularity, flatness, etc.

Technically, are any of the instructions inappropriate?

Are there any instructions that should be included?

Is the basic outline style ugly, or inefficient; has too much detail been included for steps? Would a flowchart and data tables be any easier to follow?

Feel free to hack away, I'm looking for good general suggestions. I'd also be interested in anyone's take on the technical content.

--Erik
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  Post Number #2  
Old 24th May 2006, 04:41 AM
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apestate

 
 
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The bullets & numbering is now top of the line.
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  Post Number #3  
Old 24th May 2006, 05:04 AM
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sonflowerinwales

 
 
Total Posts: 175
Looks Ok to me.
It may be an idea in clauses 4.3 to add 4.3.10, recheck of zero, and add 4.8.11, recheck of zero. I would avoid removing the spindle to oil, (4.5) as I've had more problems removing them than leaving in place. Sometimes, for no real reason, when you re-assemble, it gets tight, and you then have problems. Also I would move this para earlier in the procedure, before calibration starts, around para 4.2. One other point, what about metric equipment?
Paul
  Post Number #4  
Old 24th May 2006, 06:47 AM
apestate's Avatar
apestate

 
 
Total Posts: 518
thanks sonflowerinwales.

I was a little concerned about spindle removal and tightening of spindle and adjustments such as this, as things can get messy. I certainly won't be making instructions on how to disassemble a dial caliper, that never works.

I do like the idea of taking measurements before doing any calibration work, even cleaning.

This is a draft, of course. In the second version posted above the formatting of the outline numbering has been changed so that it's easy to tab over to bulleted point or NOTE: which seems to work nice.

what's metric?
  Post Number #5  
Old 24th May 2006, 08:40 AM
gpainter

 
 
Total Posts: 1,166
Think about making it shorter. We did most of our own calibration and no WI was over one page and had no problems.
  Post Number #6  
Old 24th May 2006, 09:02 AM
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CarolX

 
 
Total Posts: 2,169
Quote:
In Reply to Parent Post by gpainter

Think about making it shorter. We did most of our own calibration and no WI was over one page and had no problems.
I have to concur on this...my cal procedure for micrometers is a single page.

Remeber the KIS method, keep it simple.
  Post Number #7  
Old 24th May 2006, 09:20 AM
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Kevin H

 
 
Total Posts: 489
Some random thoughts - do you really want to specify temperature as 68 F, +/- 1.8 F - what are you using to measure and control the temperature that closely is it tracable to NIST, etc. Same comments for relative humidity - if you specify it you have to measure and control it and trace back to NIST. Is it even relative to micrometer calibration? (My personal opinion is that as written, it's an easy nonconformance for an auditor unless you really are controlling that closely.)

With temperature, you can justify a much wider range especially as you are only going out 3 decimal places - get the coefficient of thermal expansion for the material your gauge blocks are made of and calculate the effect of temperature on them for the temperature range you'd like to work to. (We had blocks made of 52100 steel, and the effect of temperature on them for a 40 degree F range was negligible compared to the .001 we were measuring to.

I'd try to shorten it as much as possible - substitute training/competency for extremely detailed instructions. With detailed instructions, if they are not followed and an auditor observes them not being followed you get a nonconformance. If memory serves, the one I used for the mechanical lab I ran was about 1 & 1/2 pages and was in a larger font size - it passed muster for ISO 9001:1994, QS-9000, and ISO Guide 25 (predecessor to ISO 17025)
  Post Number #8  
Old 24th May 2006, 06:55 PM
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Hershal

 
 
Total Posts: 2,464
Good beginning.....

I would add "exercising" the mic to watch for skipping or sticking which indicates the need for cleaning.....

Add the need for white gloves and have the instructions state that they must be used to pick up the gage blocks - NEVER touch gage blocks with your fingers.....

Add the requirement to document the specific path for comparison and where to find the procedure to calculate measurement uncertainty.....under international definitions for traceability, there must be an unbroken chain of comparisons to National or international standards, and there to SI and must have stated uncertenties at each step, or you do not have traceability.....

As always I strongly suggest sending items for calibration to a cal lab accredited to ANS/ISO/IEC 17025.....while I understand cost issues, metrology professionals are the best folks to handle your calibration.....

Hope this helps.

Hershal
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