How Accurate Are Low Cost Digital Calliper Micrometers?

[Jens Eirik Skogstad 1Participant @jenseirikskogstad1]

I has some old plan of model engines and steam engines, there is still imperial fractions as main measurements. To make precision work by imperial fraction measured by digital caliper is not precise as the caliber without digital. I learned out there is a gap when i moved the movable jaw a little bit at digital caliber while the digits of imperial fraction is still unchanged. Best to use the old caliber and micrometer or for digital freaks: use 1/1000" decimal instead imperial fraction when we are talking about exactly fit between two parts.

John Stevenson, we has gone out of imperial measure in wood work about 1975-1980 in Norway, all wood materials is dimensioned in centimetre and metre. For smaller wood to example hobby use is measured in millimetre.

[BazyleParticipant @bazyle]

Following the Norwegian connection – What do metricated carpenters do for measuring 19.2 iches? A bit of metric rounding could put the whole job out and leave you with a leaking roof.

[John Stevenson 1Participant @johnstevenson1]

Engineers use millimetres and metres.

Only the BBC and dressmakers use centimetres.

John S.

[Jens Eirik Skogstad 1Participant @jenseirikskogstad1]

Bazyle, we are using metricated material in old house who is builded in imperial measure to example exterior wall cladding when we are replacing 2-3 the rotten old planks in 6" with new 16 cm planks at wall cladding and we are using router to adjust right measure in 6" at oversized plank 16 cm before we dress the new adjusted planks on wall. No problem

[TerrydParticipant @terryd72465]

Posted by John Stevenson on 26/04/2012 00:57:54:

Engineers use millimetres and metres.

Only the BBC and dressmakers use centimetres.

John S.

Unfortunately so do Maths teachers and the French!   Fortuntely the decimetre seems to have disappeared

Regards

T

Edited By Terryd on 26/04/2012 07:26:24

[TerrydParticipant @terryd72465]

Posted by John Stevenson on 25/04/2012 20:15:10:

They only exist in Imperial measurement. 1/2 a metre isn't a technical term.

I quite agree John but there are still those who insist on using the so called imperial system. Btw I have been campaigning for the abolition of the centimetre for years.

Regards

T

[WALLACEParticipant @wallace]

I don't mind cm or thou' – but what I can never get is the 0.0001mm. Or is that .00001mm ?

Why not use micrometres in a similar way to the electronic fratenity who use microamps, volts or farads ?? No getting the magnifiying glass out to see how many noughts there are or where the decimal point is !.

So 2.5 micrometres is 1 thou. That seems a lot easier to read than 0.025mm !

W.

[Anonymous]

Errrr, I make 1 thou equal to 25.4µm – Andrew

[TerrydParticipant @terryd72465]

Posted by WALLACE on 26/04/2012 13:18:51:

I don't mind cm or thou' – but what I can never get is the 0.0001mm. Or is that .00001mm ?

Why not use micrometres in a similar way to the electronic fratenity who use microamps, volts or farads ?? No getting the magnifiying glass out to see how many noughts there are or where the decimal point is !.

So 2.5 micrometres is 1 thou. That seems a lot easier to read than 0.025mm !

 

W.

A thou is one thousandth of an inch or 0.001 (to state the obvious). therefore it is quite logical to talk about a hundredth of a millimetre or 0.01 (approx 4/10ths of a thou'! ) and forget imperial. It is the mixing of terms as you do that causes any confusion.  Not many folks in engineering would work to 0.001mm (approx 4 hundredths of a thou or 0.00004" – now there's a lot of noughts!) let alone 0.0001mm.

And if you find 0.01mm difficult to read how do you manage with proper engineering drawings? Now that thought I find confusing.

T

Edited By Terryd on 26/04/2012 16:21:59

[blowlampParticipant @blowlamp]

Can anyone explain why americans refer to thou's as mils?

Martin.

[Gone AwayParticipant @goneaway]

Actually, American engineers don't, generally.

I assume mils comes from the prefix "milli-". Another example of mixing systems?

[Peter G. ShawParticipant @peterg-shaw75338]

re: mils.

I used to work for BT and it's predecessors as a technician, and we always used to refer to relay distance adjustments as "mils". Interestingly, relay springs were tensioned in "g's" for grams leading to this sentence in my Telephony Vol.1, originally written in 1947 but I assume updated and corrected before I bought my copy in 1959:

"When a relay is fitted with 12 mil springs, tensions (c) & (e) are reduced to 11-15g and 21g minimum respectively, and the relay is given a green label."

To the best of my knowledge, "mils" was the same as "thous".

A possible reason for it may be due to the same logic whereby litres, metres, ohms, volts and a host of other measurements have always used prefixes such as milli- to indicate values which are one thousandth of the base value, hence if the inch is considered to be a base value, then "milli-inch" would be the thousandth part. Custom & practice, and human laziness, would soon ensure that milli-inch quickly became "mil"

Regards,

Peter G. Shaw

[Ex contributorParticipant @mgnbuk]

Can anyone explain why americans refer to thou's as mils?

I thought that the term had a military basis, to do with artillery. But a quick Google threw up the following :

a unit of angular measurement equal to ¹⁄₆₄₀₀ of 360 degrees and used especially in artillery

So that would not appear to be related to linear distance.

But other references showed :

Origin:
1715–25; short for Latin millēsimus thousandth, equivalent to mill ( e ) thousand ( see mile) + -ēsimus ordinal suffix

Regards,

Nigel B.

[Sub MandrelParticipant @submandrel]

Something rarely admitted is the way that fractional meaurements can make design a lot easier.

Imagine you have a stack of different bits, flanges, shoulders etc. that all need to add up to a particular total dimension, but their individual sizes aren't critical.

It's surprising how much easier it is in fractions.

Think of a steam cylinder with a flange each end, 1" long. 1/8" flanges and 3/4" for the body -will that do?

Neil

[mike adkins 4Participant @mikeadkins4]

ARC for one is doing these at £8.00 a pair and to be honest at this price they are consumables.

dunno if im going blind or stupid – poss both, can anyone give me a link to the arc website, im finding nothing to do with tools on google ??

[PekkaNFParticipant @pekkanf]

Mike,

http://www.arceurotrade.co.uk

This one?

Pekka

[Clive HartlandParticipant @clivehartland94829]

The Angular measurement:- MILS is of japanese origin and as stated is 6400Mils to a 360 Deg. circle. Any errors are very small and ignored.

Then at 1000 Mtrs 1 MIL will subtend 1 Mtr and so on, at 2000 Mtrs it will subtend 2 Mtrs.

10000mtrs it will subtend 10Mtrs.

Then graticules are marked in Mils and it is very easy in the Horizontal plane to see how far off a fall of shot is and use that to make angular corrections.

It makes a very good range estimate for the ranging of fall of shot on artillery and is now standard in the British army.

Hand Compasses are also marked in Mils.

Clive

[Ian AbbottParticipant @ianabbott31222]

I have a couple of digital calipers, the expensive one drains the batteries, the cheap one doesn't, go figure.

I've found that my biggest problem is that there's enough flex in the instrument to give a constantly fluctuating reading in the half a thou. or less isle. I end up physically holding the jaws together with one hand to get a steady reading, while tightening the lock screw with the other.

My favourites are my three dial calipers, one imperial, one metric and one fraction, which was given to me by a universal joint rep forty years ago.

Ian

[mike adkins 4Participant @mikeadkins4]

Posted by PekkaNF on 02/05/2012 11:49:52:

Mike,

http://www.arceurotrade.co.uk

This one?

Pekka

much appreciated

[David LittlewoodParticipant @davidlittlewood51847]

Clive,

The story of the mil is more complex than you suggest – and, BTW, I can find no trace of it having any Japanese origin.

In order to have the same relation that you set out – i.e. 1 m separation at 1000 m – the angle would have to be 1/1000 radian, or 1/6283 of a circle. This was adopted by the infantry for sighting rifles. Then for some reason the artillery decided they wanted to simplify it to 1/6400 of a circle, so that 5 binary divisions gave 100 mils (probably – though this is only my guess – because this made it easier to construct by geometry). Just to add to the confusion the US artillery had previously used the mil to represent 1/1000 of a right angle (i.e. 1/4000 of a circle).

It seems to me that the only one of these which has the merit of actually being useful is the infantry mil of 1/1000 radian. However, I have only ever come across the mil as a military unit.

Source – mainly the Oxford Dictionary of Weights and Measures.

David

Edited By David Littlewood on 08/05/2012 15:34:53

[Clive HartlandParticipant @clivehartland94829]

WILD Heerbrugg and now LEICA have always been able to supply theodolites in MILS and GRADS/400.

I have converted many standard 360Deg, instruments for various establishments. Particularly the T2 Theodolite. which is accurate to half a sec. with Auto Collimation. and similarly in the other configurations.

These being mainly used by Military and Shipbuilding. Also used to align aircraft navigation devices and weaponry, ie High Intensity Lights. and in submarines to align torpedo tubes and optical systems. They can be supplied with what is called 'Tight' standing axis so that with a fixed compensator can be used in a right angle mode to transfer lines of sight throughout a vessel.

This mode is when the instrument is fixed to a vertical surface.

Gyro based theodolites such as the ARK1 are usually in deg. and are placed in a special jig prealigned to an airframe and then the aircraft is turned and compass checks carried out.

Maybe now not needed due to Sat. Nav instrumentation.

Regards the Japanese origin I can only go by what I was taught as an apprentice and had no need to research it, only that it existed and how to use it.

Clive

[Morgan SweetParticipant @morgansweet]

Posted by Peter G. Shaw on 26/04/2012 20:48:40:

re: mils.

I used to work for BT and it's predecessors as a technician, and we always used to refer to relay distance adjustments as "mils". Interestingly, relay springs were tensioned in "g's" for grams leading to this sentence in my Telephony Vol.1, originally written in 1947 but I assume updated and corrected before I bought my copy in 1959:

"When a relay is fitted with 12 mil springs, tensions (c) & (e) are reduced to 11-15g and 21g minimum respectively, and the relay is given a green label."

To the best of my knowledge, "mils" was the same as "thous".

A possible reason for it may be due to the same logic whereby litres, metres, ohms, volts and a host of other measurements have always used prefixes such as milli- to indicate values which are one thousandth of the base value, hence if the inch is considered to be a base value, then "milli-inch" would be the thousandth part. Custom & practice, and human laziness, would soon ensure that milli-inch quickly became "mil"

Regards,

Peter G. Shaw

[Morgan SweetParticipant @morgansweet]

Peter, your reference to "mils" above as a measurement of 0.001" is quite correct.  Also was  Strowger not an American?

Edited By Morgan Sweet on 12/05/2012 20:48:21

Edited By Katy Purvis on 01/06/2015 12:27:04

[Peter G. ShawParticipant @peterg-shaw75338]

Morgan,

Yes, the Strowger System was reputedly invented by Almon B. Strowger who was indeed American, but the system was much refined into the eventual workable system that we all love. Or hate!

Having said that, the GPO as it was, initially used Strowger type selectors from a number, five I think, of different companies, which although they fitted a standard cradle and bank, were between themselves not really compatible, ie spares for Siemens, say, would not fit, say, ATE. Then, in the '30's I think it was, the GPO designed it's own Strowger selector which was called the 2000 type and all manufacturers built to this design, hence solving the spares compatibility problem.

The 2000 type selector had a number of other advantages as well over the older selectors which became known generically as pre-2000. The 2000 type switch lasted until the demise of the Strowger system in the UK although there was an attempt in the '60's to introduce a cheaper alternative. This was, unsurprisingly, known as the 4000 type selector and was functionally identical to, and hence fully interchangeable with, the 2000 type and used the same cradle and bank. However, it did not last because, I believe, it was not as reliable as the 2000 type.

Peter G. Shaw

Edited By Peter G. Shaw on 15/05/2012 17:32:02

[Will RobertsonParticipant @willrobertson16447]

To independently verify their accuracy I think it would be necessary to compare them to certified precision standards or an instrument with certified calibration but I don't have access to either of these.

I did manage to get my paws on a 25mm and a 50mm standard ( both labeled +- 0 μ ) yesterday and – sure enough – it turns out that in ideal conditions my cheap digital calipers do give a better than advertised accuracy

(PS – I remember using military compasses marked out in Mils – a special drill if you broke one of them – the glowing paint was radioactive. Microchips can never match the magic of the Strowger exchange.)

Edited By Will Robertson on 09/06/2012 21:22:00

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