# Standard For Checking Inside Micrometer



## Boswell (Apr 8, 2015)

I have a Mitutoyo .2"-1.2" inside micrometer that I purchased used. I would like to check the calibration. Can I go to the autoparts store and use the inside of a bearing race ?  Do I need to get a master ring (Ebay has lots from $20-Thousands).

Am I even asking the right question?

Thanks


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## JimDawson (Apr 8, 2015)

A master ring would be the best.  You don't know what size the bearing is, but should be within a couple of tenths, it depends on how close you want to get.  If you went to an automotive machine shop they should have master rings for setting their bore gauges.


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## darkzero (Apr 8, 2015)

I also have a digital Mitu .2-1.2" ID mic. I don't have a ring gauge for checking it, they're expensive! I just use an OD mic to set it. Probably not one of the better ways to do it but it works for me.


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## 18w (Apr 8, 2015)

Do you have a outside mike that has been calibrated to a known standard such as a gage block or micrometer standard? If so, set your outside mike to a given size and measure it with your inside mike.  Even though I have checked my inside mikes, to be honest, all the places I worked, everyone always measured the I.D. mike with a O.D. mike instead of relying on the I.D. mike measurement. Reason being that usually we were mating a parts id to a od size and that way you were only depending on one reference.
 Of course I now realize you are referring to a actual I.D. micrometer as opposed to the standard I.D inside micrometer set with interchangeable standards. As Jim said, ring gage is best for most accurate settings. 

Darrell


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## RJSakowski (Apr 8, 2015)

Boswell said:


> I have a Mitutoyo .2"-1.2" inside micrometer that I purchased used. I would like to check the calibration. Can I go to the autoparts store and use the inside of a bearing race ?  Do I need to get a master ring (Ebay has lots from $20-Thousands).
> 
> Am I even asking the right question?
> 
> Thanks


I would not use a bearing race for a calibration standard. 

It is not ideal, but you could compare it to your outside micrometer.  You should have a calibration standard that is ten times more accurate than the device being calibrated but you would at least be able to see if there is a major discrepancy.  

If you do get a master ring gage from e-bay, it would be preferable to  have it calibrated unless it came with a current calibration certificate.


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## Ebel440 (May 24, 2015)

If you want to use a bearing race you should try to measure it with a few known good tools to see what it really measures. Otherwise you won't know if any reading you get is accurate.


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## EmilioG (May 24, 2015)

You can also get a complete Mic calibration kit that comes with an Optical flat.  If the carbide faces need lapping
this can throw off your measurements.  I use gage blocks for my Etalon.  And check the spindle for excess play.
With a complete set, you can check along the length of measurement.     LIIS can check your mic also.


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## kd4gij (May 25, 2015)

Like darkzero I just use an od mic. If you are just making parts in a hobby shop that is plinty good enough.


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## kingmt01 (May 27, 2015)

I see it as Darrell said. This is the best idea to me.


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