Caliper or Micrometer's Dimensional Flatness

[garyf2017]

Hi,

For a caliper or micrometer's flatness- we don't have any lapping machine but we do check the flatness and we just note down if it's still within permissible error but once it's already out of tolerance do we still need to check it's linearity and parallelism?

Thanks

 

[dwperron]

Yes.

You have to determine if there are any other errors with your device - it could also fail parallelism or linearity. Only after you know the complete status of your device can you determine if it could possibly have negatively affected your measurement process or product.

 

[garyf2017]

Hi, dwperron thanks for your reply.

So it means that we can still released the unit as "serviceable" even if it fails other parameters?

 

[howste]

So it means that we can still released the unit as "serviceable" even if it fails other parameters?

Do the other parameters affect its serviceability? In other words if any parameter has problems that would affect the measurements being done, especially in a way that might cause you to accept bad product, then absolutely don't accept it. If you understand any effect of the parameters on the measurement and know that they won't affect the fitness for use of the gage, then you can accept it.

Usually such gages would be identified with a "limited calibration" label so if someone uses the gage for a different application they would be aware that they need to confirm its fitness for the purpose.

 

[garyf2017]

Thanks Howste...

 

[thnksnow247]

You need to verify all critical parameters of the measuring tool.

For a micrometer this would be at least flatness, parallelism, and linearity.

If the flatness is found to be out of spec, but the parallelism and linearity are good you need to consider the potential impact on product that has be previously measured with this tool. Going forward you may put the tool into service with a reduced accuracy constraint, but that gets messy and it probably better to get a new pair of mics unless it is something special.