Digital Micrometer

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

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.

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.

.

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.

I have requested a catalogue and price ist but the Royal Mail seems to have problems. I received 36 items of post today!

MC

Really?

The OP was talking of the zero reading. Set to zero the micrometer is essentially a complete ring of metal split but touching at the anvil ends. Raise the temperature of the entire instrument and all that happens is that it grows in size. The anvils will still be just touching. Think what happens to a steel ring when heated evenly.

Admittedly if you only heat the yoke (or one side of the ring) then yes you will get an error as you will when measuring anything other than zero when the whole instrument undergoes a temperature change and the error will get bigger the larger the gap. Hence the use of mic stands.

In this case it is probably dirt.

regards Martin

I thought I had produced another of my typo's, but looking at my post, it says 0.01mm.  Now I see that the size was down twice, of course I meant 0.01mm both times.

Mitutoyo make a digital micrometer that measures down to 0.0001mm, seems rather difficult to ever get the same reading twice with one of those.

Edited By old mart on 17/03/2021 20:45:35

Michael quoted what you typed, suggest a trip to Specsavers is in order

Edited By JasonB on 17/03/2021 20:46:07

I went to Specsavers twice, once to benefit from two pairs for the price of one, but when I wanted safety glasses, they would not play ball. I had to have one pair of ordinary ones. I still have two pairs of Boots glasses from about 25 years ago, they are superior to Specsavers.

Martin is correct, re the expansion as the temperature changes as long as the same materials are in both legs ie both sides of the measuring device have the same coefficient of expansion. At these high precision measurements one cannot guarantee that (carbide anvils?).

Neil’s statement that the device will measure the same at different temperatures is flawed - the screw thread pitch, if it were that type of device would change pitch as the temperature changed. His statement that stated that temperature was unimportant as long as everything was at the same temperature is only correct if the linear coefficients of expansion (of both the measuring device and item being measured) were exactly the same ie. the measuring device would have to be made from the same material as it was measuring. Not good enough, even then, as the measuring device would almost certainly wear out quite quickly.🙂

And to think this thread started off with MC ‘looking a gift horse in the mouth’....

You can think that my thinking is flawed, but do the tests for yourself. You will be enlightened.

Many mechanical micrometers are still good after 10 years of service if they are looked after and cleaned and lubricated.

Edited By Neil Lickfold on 18/03/2021 03:42:10

Seems unlikely that anyone not using a 2-micron micrometer repeatedly every day over a long period has much chance of making such fine measurements in the home shed on a hobby grade mike. Sure the digital readout says its meausuring down to 2 microns but the ratchet unit is not calibrated to that level of precision, nor is the operator's fingers for doing it by "feel" or the level of cleanliness of the mike or the job. Disregard the last digit on the readout and be happy to measure to the nearest hundredth of a millimeter which is more than plenty good enough for home use.

If the test piece is the same material as the mic then the measurement will indeed be temperature invarient. The gap will increase but so will the piece being measured.

regards Marin

I have my late Father's M&W micrometer in its Spectacle Case.

It looks as good today as it did when it was new.

I think it must date back before WWII when he joined the family company - is there any easy way of finding out when it was manufactured ?

I would use it - except that I have both metric and digital micrometers.

MC

I have my own, ditto, but mine dates to 1961 (when I bought it .... might have been manufactured a year or two previously). Still a favourite.

The first step would be to ascertain the M&W reference number and then to track down catalogues for possible relevant periods. (I assume there is no date on the instrument itself, of course).

Thank you for taking the time to respond.I have carefully looked at the Micrometer

Unfortunately there's no Serial Number - just "961"

I think that was produced over a long period.

I'll try taking photographs and see if I can find a contact for M&W

MCB

My M&W catalogue is from 1970 and so no direct help. At that time "961" was the initial element in the part numbers of a range of micrometers with varying features eg "961MF" micrometer with friction thimble.

Mine says "961B". An (anecdotal) posting on the web suggests the difference between the 961 and 961B models is that the latter reads to tenths of a thou (i.e. it has the tenths vernier) while the former does not.

Can you confirm that?

.

Page 1 of this seems to support that anecdote: **LINK**

https://www.bowersgroup.co.uk/media/wysiwyg/downloads/Moore_Wright_Spares_List_2015_April_Iss2_Oct15.pdf

MichaelG.