Micrometer Anvil Placement to measure the diameter of Steel Wires

[Mgoul]

I need help clearing up a debate regarding proper use of micrometers. We are currently using flat anvil 1" inch hand-held micrometers to measure the diameter of various steel wires.

There are quality techs that attempt to use just the barest edge of the anvil to measure OD of the wire because they think it is "more accurate".

I have always assumed it was standard practice to center the wire "more or less" in the anvil.

Can any of you shed some light on what best practice is please?

 

[Stijloor]

Re: Micrometer anvil placement

I need help clearing up a debate regarding proper use of micrometers. We are currently using flat anvil 1" inch hand-held micrometers to measure the diameter of various steel wires.

There are quality techs that attempt to use just the barest edge of the anvil to measure OD of the wire because they think it is "more accurate".

I have always assumed it was standard practice to center the wire "more or less" in the anvil.

Can any of you shed some light on what best practice is please?

Anvils of a micrometer are supposed to be flat. That is one of the checks performed during calibration. Typically, an optical flat and a monochromatic light source is used to very this flatness within a predetermined number of light bands. OK. So, in principle, it should not make any difference. If your quality techs suspect out-of-flatness, then it's time for calibration right??

Establish one measuring method, stick with it, and thus reduce measurement system variation. Have you ever considered an MSA study? (Measurement System Analysis)

Good luck!

 

[Mgoul]

I didn't explain my concern very well.

When the technicians in question use the edge of the anvil to measure an OD I feel it opens us to the possibility that they may not get to the high center of the wire. There must be times when they approach from the side, make contact a little shy of the high center and report a slightly undersized diameter.

To my point, there is a lab tech that has rejected an inordinate number of wires due to slightly under spec ODs and he uses the "side anvil method".

 

[AndyN]

I didn't explain my concern very well.

When the technicians in question use the edge of the anvil to measure an OD I feel it opens us to the possibility that they may not get to the high center of the wire. There must be times when they approach from the side, make contact a little shy of the high center and report a slightly undersized diameter.

To my point, there is a lab tech that has rejected an inordinate number of wires due to slightly under spec ODs and he uses the "side anvil method".

Are you measuring a spring or something made from wire which restricts the access of the whole micrometer? If so, there are special frames, anvils etc to allow for wire measurements. Otherwise, it seems you need to do some studies with these technicians to show them what they are doing is causing issues.

 

[Mgoul]

No we are measuring straight wires over the OD. Nothing tricky.

 

[AndyN]

In that case, you should probably do a couple of things. Some one-to-one coaching on use of micrometers, maybe with a cal. lab supplier (technician) there, with their set of optical flats so your guys can see the anvil is flat. Then have them make measurements and plot them across the face of the anvil to show there's no variation. Also ask them, of course, why, they think doing it their way is beneficial...

 

[CRYOSILVER]

In a case like this, I'd issue the techs a V anvil micrometer, so as to ensure centered contact of the anvil to the wire. As an alternative, compare the "centered" measurement and the "edge" measurement to a third method, such as measuring the wire between a surface plate and a dial indicator and see which is more "true."

If you have one tech rejecting more wires than others, a gage R&R on the measurement of this diameter might be a good place to start determining what's happening here.