Digital Micrometer

[Dr. MC BlackParticipant @dr-mcblack73214]

I was given a Digital Micrometer as a gift. It arrived in a Wooden foam lined box.

I used it yesterday to measure something having set it to zero by using the ratchet and pressing the reset button

After finishing the measurement, I closed the jaws again using the ratchet and the display read 0.002mm

That's NOT what I would expect!

Am I doing something wrong? Or shall I dispose of the micrometer?

I do NOT leave the little button cell installed when the instrument is NOT in use – just in case it leaks!

Any suggestions or comments, please?

MC Black

[Dr. MC BlackParticipant @dr-mcblack73214]

Zero problem

[David George 1Participant @davidgeorge1]

Hi MC have you thought about the temperatures at this time of year. If you have stored if in a cooler temperature then get it out and use it there could be a difference in readings. The standard temperature is 20 deg C end whilst at work the factory had to kept at this temperature. I would get the micromiter out and give it a while to stabilise to work area temperature before setting up and using it.

David

[JourneymanParticipant @journeyman]

A 2 micron discrepancy could be caused by temperature (as David says) a minute speck of dust, a slight difference in pressure from the ratchet or almost anything. I am surprised that your micrometer reads down to that level on most the third decimal place is usually only 0 or 5.

John

[KWILParticipant @kwil]

This sounds like a digital vernier/caliper, hardly a micrometer. At best these devices are comparators and not for true measurements.

[Howard LewisParticipant @howardlewis46836]

When using a digital calliper, I always check the Zero before taking the measurement.

2 microns is not a large error, but you may be finding the limit of resolution of the instrument.

It could be the clearance between Thimble and Barrel threads!

Fuel injection equipment was made with those sorts of clearances, for 500 – 600 bar pressures, probably even less with current high injection pressures. of 1,500 bar.

It could even be inconsistency in the ratchet, or its use.

Was the micrometer at the same temperature each time, or was it affected by the heat of your hand, or even your breath?

A Standards Room or Calibration Room will not consider measuring anything until it has "soaked" to the ambient temperature of the room for at least 24 hours.

Did you turn the ratchet and thimble at the same rate both times? So that the momentum was the same, as far as possible.

Taking an extreme example, you won't drive a nail home by pressing the hammer on its head. But you will when it comes flying down at speed!

Bear in mind that a human hair is about 125 microns (Varies between 75 and 175 depending on colour )

Howard

Edited By Howard Lewis on 16/03/2021 12:11:29

[Bo’sunParticipant @bosun58570]

Good afternoon MC,

As David says. Temperature could well be the culprit. After all, 0.002mm (0.00008&quot is two tenths of not very much.

I think I'd be happy with that. Certainly for model engineering.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Howard Lewis on 16/03/2021 12:09:14:

.

2 microns is not a large error […]

Bear in mind that a human hair is …

.

From a previous discussion:

Here’s a useful ‘benchmark’ image, courtesy of Wikipedia:

…. a 50 micron human hair, and a 6 micron carbon filament in the same frame:

**LINK**

https://en.wikipedia.org/wiki/Micrometre#/media/File:Cfaser_haarrp.jpg

.

MichaelG.

[Dr. MC BlackParticipant @dr-mcblack73214]

Posted by David George 1 on 16/03/2021 11:59:39:

Hi MC have you thought about the temperatures at this time of year. If you have stored if in a cooler temperature then get it out and use it there could be a difference in readings. The standard temperature is 20 deg C end whilst at work the factory had to kept at this temperature. I would get the micromiter out and give it a while to stabilise to work area temperature before setting up and using it.

David

Thank you for taking the time to respond.

The Micrometer was stored indoors (in my kitchen) where I did the measuring.

So I don't think the difference was due to temperature – but it's a good thought.

MC

[Tony Pratt 1Participant @tonypratt1]

0.002 mm is nothing to worry about.

Tony

[Oily RagParticipant @oilyrag]

I was taught during my apprenticeship never to use the ratchet on a micrometer, always to 'feel' the contact point at which to take the reading. The reason? ratchets are inconsistent and not a consistent way to measure anything, better to develop the 'feel'.

[Mike PooleParticipant @mikepoole82104]

Did you clean the micrometer faces before zeroing? I use a piece of clean paper gripped lightly between the faces and then drawn gently out of the faces. Be sure to not grip too tightly and produce paper dust. With the anvil faces clean, close and zero. If you can indicate thousandths of a millimetre then your technique is going to be very good to get repeatable readings. If you have access to slip gauges then measure some and see if your technique with the ratchet or thimble agrees with the slip gauge, you will be doing well if you get repeatable readings and if the reading agrees perfectly with the slips then you have a fantastic mic.

Mike

Edited By Mike Poole on 16/03/2021 13:16:46

Edited By Mike Poole on 16/03/2021 13:18:13

[Dr. MC BlackParticipant @dr-mcblack73214]

Posted by Oily Rag on 16/03/2021 12:37:08:

I was taught during my apprenticeship never to use the ratchet on a micrometer, always to 'feel' the contact point at which to take the reading. The reason? ratchets are inconsistent and not a consistent way to measure anything, better to develop the 'feel'.

Thank you for taking the time to respond.

I was taught, over 50 years ago, to always use the ratchet!

I don't use a micrometer sufficiently often to develop a feel!

MC

[Dr. MC BlackParticipant @dr-mcblack73214]

Posted by Mike Poole on 16/03/2021 13:16:03:

Did you clean the micrometer faces before zeroing? I use a piece of clean paper gripped lightly between the faces and then drawn gently out of the faces. Be sure to not grip too tightly and produce paper dust. With the anvil faces clean, close and zero. If you can indicate thousandths of a millimetre then your technique is going to be very good to get repeatable readings. If you have access to slip gauges then measure some and see if your technique with the ratchet or thimble agrees with the slip gauge, you will be doing well if you get repeatable readings and if the reading agrees perfectly with the slips then you have a fantastic mic.

Mike

Thank you for taking the time to respond.

I didn't think to clean the faces.

I'll try to remember about doing that in the future but would expect the original reading to be greater than the final reading if the faces had been dirty.

The only calibration opportunities that I have are one inch and 3 inch standards – neither much help with a 0-25mm instrument!

MC

[EmgeeParticipant @emgee]

I follow the same cleaning method as Mike and check occasionally on a slip, but to get used to using the mic with the same force you can use an HSS or carbide tool shank, when you get the same reading 8 out of 10 you will be confident measuring parts.

Emgee

[Michael GilliganParticipant @michaelgilligan61133]

Posted by MC Black on 16/03/2021 14:07:34:

[…]

I didn't think to clean the faces.

I'll try to remember about doing that in the future but would expect the original reading to be greater than the final reading if the faces had been dirty.

.

.

Unfortunately, it is entirely plausible that a two micron dust particle landed on one anvil during the time you were conducting the test … unless, of course, you have full HEPA filtration throughout your working environment.

MichaelG.

.

Edit, for context:

https://www.ristenbatt.com/xcart/Vacuum-Cleaner-Filtration-Efficiency.html

Edited By Michael Gilligan on 16/03/2021 14:20:31

[not done it yetParticipant @notdoneityet]

Posted by Journeyman on 16/03/2021 12:05:22:

A 2 micron discrepancy could be caused by temperature (as David says) a minute speck of dust, a slight difference in pressure from the ratchet or almost anything. I am surprised that your micrometer reads down to that level on most the third decimal place is usually only 0 or 5.

John

Agreed, John, re the temperature – even in a kitchen environment. Mine resolves to 0.001mm – but who on here really needs that third figure to be absolutely accurate? (Only Howard with fuel injection equipment, maybe?)

I think mine was likely rejected due to a tiny chip on one anvil edge. I find using the ratchet is close enough for me!

IF that micrometer is only a 0-25mm, the error is not great. If it happens to be a 25-50mm, or larger, that error becomes virtually non-existent – even if there is a similar error at the reading value!

I don’t think I would be giving MC a horse as a gift.🐎

[Dr. MC BlackParticipant @dr-mcblack73214]

Posted by not done it yet on 16/03/2021 14:21:03:

I don’t think I would be giving MC a horse as a gift.🐎

Thank you for taking the time to respond.

I don't want a horse, Thank you.

They are nasty smelly creatures that bite at one end and fertilise rhubarb at the other.

I'm NOT sure that my steel toecap safety boots could withstand even a stationary horse on them.

With best wishes and thanks again.

MC

[Anonymous]

Posted by MC Black on 16/03/2021 11:47:34:

After finishing the measurement, I closed the jaws again using the ratchet and the display read 0.002mm

That's NOT what I would expect!

oooh I wish my digital mic could measure to that level of accuracy and repeatability. I'm sure I could dream up a use for it if it could.

…. oh …. wait ….. we're not talking accuracy or repeatability we're talking digital display reading.

Ah well …

[Dave HalfordParticipant @davehalford22513]

What do you make MC?

[Dr. MC BlackParticipant @dr-mcblack73214]

I have inherited a lot of tools et hoc genus omne from my late father (and another friend) and have been spending warmer days during the Covid-19 pandemic lockdown restoring them

When my workshop is sorted out, I look forward to making some model engines

I recall seeing in an Axminster catalogue several years ago a kit for an engine suitable for beginners but it's NOT in their current catalogue

Does anybody have the drawings for that which they would be prepared to share, please?

(Perhaps I should have started a new thread for that?)

With best wishes.

MC

[noel shelleyParticipant @noelshelley55608]

You could do a lot worse than have a look at Stuart Models, they start small and go upt a good size. Noel.

[old martParticipant @oldmart]

Regarding digital micrometers, it is easy to be too worried about the repeatability and the actual dimensions involved. I worked making aircraft parts for many years and looked at thousands of drawings. 99% of those drawings did not specify tolerances tighter than +- 0.01 microns. And aircraft parts are more closely inspected than most things. Any parts deemed critical have all their origin, heat treatment, dimensions and finish checked 100%.

A micrometer that has graduations of 0.01mm will give all the needs of general measurement, and one calibrated in 0.001" can be read easily to 0.0005" or better.

I had 3 digital Mitutoyo micrometers, and sold them all last year, I can still manage my metric and imperial mechanical mics.

[Neil LickfoldParticipant @neillickfold44316]

A 5 deg change in temp on a 0-25 micrometer will result in a reading error of 2um to 3 um . You can do that test yourself. Needed is a thermometer and take a reading at the temp it is at. Then hold in your hands until it has warmed another 5 dec warmer. Re zero and you will see the difference in the readings. As most things are relative, and not absolute, if you are measuring a steel part , and the total environment is around the same, so same temp part and same temp measuring instrument, the dimensions will still be correct if the mic was zero at that temp. Making parts to less than 5um always becomes a challenge, especially when they are larger than 30mm diameter and length.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by old mart on 17/03/2021 18:20:46:

[…]

99% of those drawings did not specify tolerances tighter than +- 0.01 microns. […]

.

I would confidently presume that 100% of them did not specify tolerances tighter than +- 0.01 microns.

I work [O.K. I play] a lot with microscopes, and 0.01 microns is very small indeed !

Would it be reasonable to guess that you meant +/- 0.01 mm [i.e. +/- 10 microns] ?

MichaelG.

[Author]

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