Micrometer Calibration Methods

P

palmer

#1
We are a manufacturer of weld wire fabric for the concrete industry. We were recently asked by Texas DOT how we calibrated our micrometers.

Is there a way to calibrate micrometers besides setting the adjustment to zero when completely closed?
 
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Jim Wynne

Staff member
Admin
#2
Re: micrometer calibration

We are a manufacturer of weld wire fabric for the concrete industry. We were recently asked by Texas DOT how we calibrated our micrometers.

Is there a way to calibrate micrometers besides setting the adjustment to zero when completely closed?
I think they wanted to know about your calibration procedure and not about how you zero the micrometer prior to use. Do you have a calibration process, whereby devices are compared to standards and adjusted if necessary? There's usually more to calibration than that, but it's a start.
 

Solinas

Involved In Discussions
#3
N

NumberCruncher

#4
Hi Palmer

The articles indicated by Solinas are good and well worth reading.

The advice regarding calibrating callipers, micrometers e.t.c. can be boiled down to one statement.

Get certified gauge blocks.

There is a lot more to calibration than just buying the blocks (just read the articles), however, without certified gauge blocks, you cannot calibrate.

NumberCruncher
 
J
#5
We are a manufacturer of weld wire fabric for the concrete industry. We were recently asked by Texas DOT how we calibrated our micrometers.

Is there a way to calibrate micrometers besides setting the adjustment to zero when completely closed?
Great advice and links already.

To summarize a bit...There is a LOT to calibrating any tool besides just checking the zero point. There may be wear issues or damage. Wear can cause problems with repeatability or cause error over distance. The contact points of the tool can also wear so that they are no longer flat and parallel to one another etc...
The depth and complexity of the calibration procedure you devise, can vary depending on the type of work you do and degree of precision required, but in almost every case it is going to require more than simply checking the zero point.

Peace
James
 
P

palmer

#6
We make several different diameters of wire "rebar" anywhere from 1/8" to 3/4".

We have pins that we have purchased for verification of wire size. We ar now using these pins as a source to calibrate the micrometers.

As part of our testing on some of our wires, we have to cut a length and weigh it. This is usually between 1/2# - 1#. They wanted to know how we calibrate the scales for this.

We had our outside contractor for our large scales perform the calibration and have added these scales to our list for annual calibration.

Amazing what you can find yourself getting in to nowadays....:rolleyes:
 
J
#7
We make several different diameters of wire "rebar" anywhere from 1/8" to 3/4".

We have pins that we have purchased for verification of wire size. We are now using these pins as a source to calibrate the micrometers.
This may be adequate for your industry. If you have pins that correspond to each wire size, one could even say that you are, in a sense, using the mic's as a "transfer gage".
I wonder if the tolerancing on rebar wire is such that micrometer's are even necessary? Seems that Calipers would be adequate to the task.
Just wondering....

As part of our testing on some of our wires, we have to cut a length and weigh it. This is usually between 1/2# - 1#. They wanted to know how we calibrate the scales for this.

We had our outside contractor for our large scales perform the calibration and have added these scales to our list for annual calibration.

Amazing what you can find yourself getting in to nowadays....:rolleyes:
Yep is surely is.
 

BradM

Staff member
Admin
#8
To summarize a bit...There is a LOT to calibrating any tool besides just checking the zero point. There may be wear issues or damage. Wear can cause problems with repeatability or cause error over distance. The contact points of the tool can also wear so that they are no longer flat and parallel to one another etc...
The depth and complexity of the calibration procedure you devise, can vary depending on the type of work you do and degree of precision required, but in almost every case it is going to require more than simply checking the zero point.

Peace
James
:agree::yes:

To add a bit more to this, there is determining how the operators use the micrometers/calipers. If they "click", do the operators let them click 1 time, 3 times, 4 times? With calipers, how much pressure do they apply to the device?

Also, get a set of gauge blocks, with an extra set of the needed sizes to use while those are being verified. I would always suggest getting data with it, and reviewing the data. Be sure and keep an eye for any gauge block that is nearing acceptable tolerance and replace before it exceeds. It cuts down on the headaches. :tg:
 

BradM

Staff member
Admin
#9
We make several different diameters of wire "rebar" anywhere from 1/8" to 3/4".

We have pins that we have purchased for verification of wire size. We are now using these pins as a source to calibrate the micrometers.
I think that is good. But as James already stated, parallelism and flatness are also a consideration for the micrometers. Too, not sure if these micrometers are ever used for any other material/ diameter/ etc. than that of the pin gauges. If so, you might want to perform some verifications outside of the pin gauges sizes you current use.

As part of our testing on some of our wires, we have to cut a length and weigh it. This is usually between 1/2# - 1#. They wanted to know how we calibrate the scales for this.

We had our outside contractor for our large scales perform the calibration and have added these scales to our list for annual calibration.

Amazing what you can find yourself getting in to nowadays....:rolleyes:
Just make sure they are performing calibrations on both the large scales and the analytical balances across your range of use. Handbook 44 does allow for reduced range of testing for large scales. Hopefully they are performing corner loads also.

For both, determine the stated accuracies of the devices. If you can set a broader tolerance than the stated accuracies, then I would take advantage of it.

Make sure that both have the resolution required for your purpose. :)
 
P

palmer

#10
Our wire tolerance is +.060"/- .003". Unbelievable for reinforcement of concrete but it is engineered to withstand so much presssure and weight. If the wire is too big it can upset the engineered material if it is to be put together with other pieces of structure.

The thing is, if you go to the high side, you are giving away wire. The closer to the negative side the more money you make. We make and sell millions of tons of wire.
 
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