Does this calibration method of a specific fixture make sense?

  • Thread starter qualitygoddess - 2010
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Q

qualitygoddess - 2010

#1
Hello:

I have read through other prior threads and postings regarding go/no go gauge calibration. I have a question regarding a specific fixture and our plan to calibrate it prior to use. I would appreciate your input if you think this makes sense.

1. we are assembling various components inside a large box made of sheet metal. The customer had us build a fixture #1 on which we place the box for assembly. There are locating pins on the fixture, and the box has corresponding machined holes that allow it to rest on the fixture and stay in one place. FYI, fixture #1 is bolted to the floor and made from a painted metal stock that has been welded together.
2. the customer had us build a checking fixture #2 to verify that the fixture #1 was "in calibration". That fixture #2 has been verified for form and fit, such as it is made from a material with excellent dimensional stability and we know that its alignment holes are in the right place (using calibrated devices at the machine shop). We are calling fixture #2 calibrated. We have defined storage and handling conditions for fixture #2.
3. fixture #2 is then used to calibrate fixture #1 via a visual verification that the holes and pins fit together. If they do, then fixture #1 is within the tolerances for x and y dimensions we have to meet for overall size and squareness.
4. for records, I plan to keep the initial verification done for fixture #2 from the machine shop, and put it's re-calibration on a 2 year cycle (it gets used 10-15 times per year). I will also keep records of the calibration of fixture #1 each time we use fixture #2 to check it.

Does this make sense?
Thanks!
 
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somashekar

Staff member
Super Moderator
#2
Re: Does this calibration method make sense?

Hello:

I have read through other prior threads and postings regarding go/no go gauge calibration. I have a question regarding a specific fixture and our plan to calibrate it prior to use. I would appreciate your input if you think this makes sense.

1. we are assembling various components inside a large box made of sheet metal. The customer had us build a fixture #1 on which we place the box for assembly. There are locating pins on the fixture, and the box has corresponding machined holes that allow it to rest on the fixture and stay in one place. FYI, fixture #1 is bolted to the floor and made from a painted metal stock that has been welded together.
2. the customer had us build a checking fixture #2 to verify that the fixture #1 was "in calibration". That fixture #2 has been verified for form and fit, such as it is made from a material with excellent dimensional stability and we know that its alignment holes are in the right place (using calibrated devices at the machine shop). We are calling fixture #2 calibrated. We have defined storage and handling conditions for fixture #2.
3. fixture #2 is then used to calibrate fixture #1 via a visual verification that the holes and pins fit together. If they do, then fixture #1 is within the tolerances for x and y dimensions we have to meet for overall size and squareness.
4. for records, I plan to keep the initial verification done for fixture #2 from the machine shop, and put it's re-calibration on a 2 year cycle (it gets used 10-15 times per year). I will also keep records of the calibration of fixture #1 each time we use fixture #2 to check it.

Does this make sense?
Thanks!
Makes perfect sense ... but just call your this procedure a verification method.
 
Last edited:

bobdoering

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#3
Re: Does this calibration method make sense?

Makes perfect sense ... but just call your this procedure a verification.
I would say it looks adequate. As long as the gages used to verify the master is within its specifications are calibrated and at least 4:1 or 10:1 more accurate than the print callouts, you can feel free to call it calibration (as it is traceable). Be sure to check for hole ID wear, too.
 

somashekar

Staff member
Super Moderator
#4
Re: Does this calibration method make sense?

I would say it looks adequate. As long as the gages used to verify the master is within its specifications are calibrated and at least 4:1 or 10:1 more accurate than the print callouts, you can feel free to call it calibration (as it is traceable). Be sure to check for hole ID wear, too.
When F#2 is used on F#1 the resulting record is an attribute and not a measureable value. Hence I could not think of how a traceability can be established. For this reason I hesitated to call this check procedure a calibration.
 

bobdoering

Stop X-bar/R Madness!!
Trusted Information Resource
#5
Re: Does this calibration method make sense?

When F#2 is used on F#1 the resulting record is an attribute and not a measurable value. Hence I could not think of how a traceability can be established. For this reason I hesitated to call this check procedure a calibration.
There really is no definitive definition of the terms. I would go with calibration because of traceability. I have not come across anything that would convince me that attribute versus variable results trumps traceability and makes it verification. Certainly the inability to adjust does not come into play. Although the terms are tossed about in discussion, if a customer requested using a 'calibrated gage', I would say this qualifies since 1) it is traceable and 2) the customer themselves probably have made no distinction between calibration and verification.
 
D

David Hartman

#6
Re: Does this calibration method make sense?

Sounds perfectly adequate. Your gage number 2 is what the old Mil specs would have referred to as a transfer gage. Just ensure that the traceability is capable of going back to NIST (i.e. the specific calibrated instruments used to "calibrate" gage 2 are traceable to NIST), this would provide full closure to the trace issue.
 
S

sitapaty

#7
Hello:

I have read through other prior threads and postings regarding go/no go gauge calibration. I have a question regarding a specific fixture and our plan to calibrate it prior to use. I would appreciate your input if you think this makes sense.

1. we are assembling various components inside a large box made of sheet metal. The customer had us build a fixture #1 on which we place the box for assembly. There are locating pins on the fixture, and the box has corresponding machined holes that allow it to rest on the fixture and stay in one place. FYI, fixture #1 is bolted to the floor and made from a painted metal stock that has been welded together.
2. the customer had us build a checking fixture #2 to verify that the fixture #1 was "in calibration". That fixture #2 has been verified for form and fit, such as it is made from a material with excellent dimensional stability and we know that its alignment holes are in the right place (using calibrated devices at the machine shop). We are calling fixture #2 calibrated. We have defined storage and handling conditions for fixture #2.
3. fixture #2 is then used to calibrate fixture #1 via a visual verification that the holes and pins fit together. If they do, then fixture #1 is within the tolerances for x and y dimensions we have to meet for overall size and squareness.
4. for records, I plan to keep the initial verification done for fixture #2 from the machine shop, and put it's re-calibration on a 2 year cycle (it gets used 10-15 times per year). I will also keep records of the calibration of fixture #1 each time we use fixture #2 to check it.

Does this make sense?
Thanks!
Document a calibration work instruction in the lines you have described.Fix periodicity of calibration.It will meet the requirements.
sitapaty
 
A

alspread

#8
I think it sounds okay too. It has to comply with the following

Where necessary to ensure valid results, measuring equipment shall
a) be calibrated or verified, or both, at specified intervals, or prior to use, against measurement standards traceable to
international or national measurement standards; where no such standards exist, the basis used for calibration or
verification shall be recorded (see 4.2.4);
b) be adjusted or re-adjusted as necessary;
c) have identification in order to determine its calibration status;
d) be safeguarded from adjustments that would invalidate the measurement result;
e) be protected from damage and deterioration during handling, maintenance and storage.


F1 is your measuring equipment and F2 is the calibration standard. See clause a above.

Good Luck
 
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