Digital Calipers – Can you rank these from the measurements?

[Peter G. ShawParticipant @peterg-shaw75338]

In respect of battery eating, some years ago I came across a site where a contributor having suffered from this problem did some on/off tests and discovered that only one of the electronic calipers actually switched off the device. I think this was the Mitutoyo. All the others did was to switch off the display.

Also, the point about batteries is worth shouting loud and clear. There are two technologies of small button cells, alkaline (eg LR44) and silver oxide (eg SR44), of which the silver oxide is a slightly higher voltage than the alkaline and which also lasts longer. The problem I have found is that although they are nominally the same, shopkeepers don't know the difference, don't understand the difference, and take umbrage if you try to correct them. So now if I'm offered alkaline, I say "No thanks", and walk out. My advice is to stay well clear of the alkaline cells for these single cell devices.

About the testing I did and temperature. When I did my tests, I left all devices overnight in the same warm room in order to have them all stabilized at the same temperature, not necessarily 25 Deg C, but whatever the heating was set at (probably 20 – 22 deg C). The three standards actually have a plastic part by which they are to be handled, whilst the instruments were mounted in the plastic jaws of a small table vice which itself had been left overnight. I thus attempted to reduce any temperature effects to a minimum.

Peter G. Shaw

ps. Anyone a pair of LR44 cells dating from February 2010? No? Thought not!

Edited to add post script

Edited By Peter G. Shaw on 27/09/2016 11:31:27

[Neil WyattModerator @neilwyatt]

Something I don't go into much in my article but I should have made more of – for a digital caliper to work at its best you need to adjust the gib screws.

Neil

[Peter G. ShawParticipant @peterg-shaw75338]

Shouldn't need saying Neil.

Peter

[SillyOldDufferModerator @sillyoldduffer]

Posted by HughE on 26/09/2016 21:08:04:

Has anybody compared a digital caliper with venier of similar quality?

As mention previously for accurancy l use a mic everytime.

My Lidle caliper is great for quick and rough measurements 0.1 mm batteries last for ever, I only use quality batteries.

Hugh

I have one of those too. It's kept upstairs for rough work when I'm playing electronics.

The main trouble with this one is reading the vernier. The picture demonstrates parallax error very well – the camera must have been off centre. Actually, from directly overhead the reading is closest to 24.05, but it's hard to tell the difference between this and 24.1 or even 24.15. A magnifying glass helps.

Much better than a 6" rule though.

Dave

[SillyOldDufferModerator @sillyoldduffer]

Posted by Neil Wyatt on 27/09/2016 11:29:32:

Something I don't go into much in my article but I should have made more of – for a digital caliper to work at its best you need to adjust the gib screws.

Neil

I didn't even know they have gib screws that can be adjusted!

Ignorance is bliss.

Dave

[SillyOldDufferModerator @sillyoldduffer]

Posted by Michael Gilligan on 27/09/2016 08:31:50:

Posted by SillyOldDuffer on 26/09/2016 13:31:49:

…

Average of Five Readings (mm)

…

Standard Deviation (mm)

'

I'd be grateful though for any comments that might improve my technique.

Cheers,

Dave

.

Dave ,

Several good points have been made already, but I think your statistical techniqe might also need improving.

…

MichaelG.

It's a fair cop Michael. The sample size is far too small to be more than 'interesting'.

When posting results I try to be open and honest about the data and how it was collected. It's amazing how easy it is to unconsciously mislead oneself, which is why I'm a great believer in peer review even if it's, ahem, robust.

Cheers,

Dave

[richardandtracyParticipant @richardandtracy]

Posted by Hopper on 27/09/2016 02:39:40:

…Regardless of the accuracy of the calipers (and ours were Mitutoyo verniers so probably pretty good) it is regarded that they just don't have as good a "feel" as a mike when taking a careful measurement. Also, using the ratchet on a mike was frowned upon as calibration of the ratchet is never reliable. A good tradesman was expected to have his own inbuilt calibrated feel when using the mike, developed from practice.

Edited By Hopper on 27/09/2016 02:43:49

Got to take the base material & form into account too.

I regularly turn plastics for pen making. The ratchet click load on my mic is way, way too compressive for a thin wall plastic tube (frequently <1mm) as found on some designs of barrels & caps and it distorts the tube like anything. It often ends up with me getting a better measurement with a calliper. I try to go to a precision of around 0.02mm as that is getting to the limits of machinability on many acrylic alloys. To get closer than that reliably you have to do lathe sanding.

Regards,

Richard

[David CambridgeParticipant @davidcambridge45658]

Over the last few years I’ve noticed lots of debate on cheap (ebay – £8.99) vs expensive Mitutoyo calipers, and to be honest I think you are all neglecting to mention the biggest and most important difference. Cheap calipers are impossible to drop no matter how hard you try. Whereas you only have to look at expensive calipers and they will slide off the bench and crash onto the concrete floor.

Tell me I’m wrong ….

Edited By David Cambridge on 27/09/2016 12:59:46

Edited By David Cambridge on 27/09/2016 12:59:57

Edited By David Cambridge on 27/09/2016 13:02:52

[SillyOldDufferModerator @sillyoldduffer]

Posted by richardandtracy on 27/09/2016 12:44:37:

Posted by Hopper on 27/09/2016 02:39:40:

…Regardless of the accuracy of the calipers (and ours were Mitutoyo verniers so probably pretty good) it is regarded that they just don't have as good a "feel" as a mike when taking a careful measurement. Also, using the ratchet on a mike was frowned upon as calibration of the ratchet is never reliable. A good tradesman was expected to have his own inbuilt calibrated feel when using the mike, developed from practice.

Edited By Hopper on 27/09/2016 02:43:49

Got to take the base material & form into account too.

I regularly turn plastics for pen making. The ratchet click load on my mic is way, way too compressive for a thin wall plastic tube (frequently <1mm) as found on some designs of barrels & caps and it distorts the tube like anything. It often ends up with me getting a better measurement with a calliper. I try to go to a precision of around 0.02mm as that is getting to the limits of machinability on many acrylic alloys. To get closer than that reliably you have to do lathe sanding.

Regards,

Richard

Good point Richard.

I've just finished collecting data after working with each callper to learn how hard I need to press the thumb-wheel to get consistent results.

Three of the calipers work best with firm pressure, certainly enough to deform a plastic tube. The fourth (the £9.99 model) works best with a much lighter touch and would be much more useful for your needs than the others.

Neil's comment about adjusting gibs could be relevant to the amount of thumb-wheel pressure needed.  More testing to do!

Dave

Edited By SillyOldDuffer on 27/09/2016 14:01:20

[SillyOldDufferModerator @sillyoldduffer]

I spent time learning just how much thumb-wheel pressure to apply to each Digital Caliper. A bit of practice and careful positioning of the jaws makes quite a difference. Three Calipers work best with the same firm pressure, the fourth (£10 model) works best with a gentle touch.

Unlike the first round of measurements, the Calipers all spent the night in the same room to make sure they were soaked to the same temperature, 18℃.

I took extra care to clean the Calipers generally and also by sliding clean paper between the jaws. Even though the Calipers were cleaned yesterday I was able to remove more dirt. The precision parallel and worktop were cleaned and clean paper was laid on top. I wore new latex gloves and a clean apron.

I took care not to touch the parallel or Calipers more than necessary. As it took 20 seconds to enter the result of each measurement the Calipers had some time to cool off after handling. This is based on Neil's hint that the electronics are temperature sensitive.

I took twelve measurements each of the 24mm dimension and graphed the variation from assumed truth, ie ±24.00mm

• The red line is the most expensive caliper. It is by far the most consistent but it reads 0.01mm high. Mean 24.011.
• The blue line is the cheapest caliper. It reads closest to 24mm but has a tendency to read 0.01mm low. Mean 23.997.
• The yellow line is the £30 caliper. It's not quite as consistent as the blue line and reads slightly lower too. Mean 23.987.
• The green line is the worst performer. It's the £10 DIY store caliper. Mean 24.015 but notice that wavy line which is not good.

The surprise is just how good the £4.99 caliper bought from Lidl is.

I actually took four sets of measurement for each caliper:

1. 24mm measured using half the jaw depth
2. 6mm measured using half the jaw depth
3. 24mm measured with the jaw tips
4. 6mm measured with the jaw tips

Measuring with jaw tips only looks to be less accurate and it also seems as if measurements taken at 6mm are more accurate than those taken 24mm. I haven't done the graphs yet but will post them later if they're interesting enough. It would be nice to see the expensive caliper measuring equally well across the range whilst the cheaper ones don't.

+1 for everyone using micrometers for accurate work!

Cheers,

Dave

Edited By SillyOldDuffer on 27/09/2016 16:19:53

Edited By SillyOldDuffer on 27/09/2016 16:21:05

[AjohnwParticipant @ajohnw51620]

Posted by Hopper on 27/09/2016 02:39:40:

In industry only ever sawcalipers used for "rough" measurements. Mikes were always used for the precision stuff, eg any diameter turned on the lathe that needs to be within a thou or so, shaft fits etc

Regardless of the accuracy of the calipers (and ours were Mitutoyo verniers so probably pretty good) it is regarded that they just don't have as good a "feel" as a mike when taking a careful measurement. Also, using the ratchet on a mike was frowned upon as calibration of the ratchet is never reliable. A good tradesman was expected to have his own inbuilt calibrated feel when using the mike, developed from practice.

Edited By Hopper on 27/09/2016 02:43:49

I'm glad some one else knows that the ratchets are dubious. It's worth bearing in mind the area and pressure effects as well. Bar is generally easy. Flat surfaces not so easy and in practice will need more pressure.

Telescopic gauges are interesting. I found that to get a real size for the diameter of a bore they need to be pretty tight fit when they are swung through on the actual diameter. As the ends are domed they are more or less point contact devises.

I have an old set of Kanon verniers. They are very precise but have the same problems as the digital ones. Used correctly they will measure to 1 thou and a very rough guestimate of over or under can be made. They were supplied for toolmaking so would be to workshop standard.

John

–

[Neil WyattModerator @neilwyatt]

Posted by SillyOldDuffer on 27/09/2016 16:19:01:

I spent time learning just how much thumb-wheel pressure to apply to each Digital Caliper. A bit of practice and careful positioning of the jaws makes quite a difference. Three Calipers work best with the same firm pressure, the fourth (£10 model) works best with a gentle touch.

Unlike the first round of measurements, the Calipers all spent the night in the same room to make sure they were soaked to the same temperature, 18℃.

I took extra care to clean the Calipers generally and also by sliding clean paper between the jaws. Even though the Calipers were cleaned yesterday I was able to remove more dirt. The precision parallel and worktop were cleaned and clean paper was laid on top. I wore new latex gloves and a clean apron.

I took care not to touch the parallel or Calipers more than necessary. As it took 20 seconds to enter the result of each measurement the Calipers had some time to cool off after handling. This is based on Neil's hint that the electronics are temperature sensitive.

I took twelve measurements each of the 24mm dimension and graphed the variation from assumed truth, ie ±24.00mm

• The red line is the most expensive caliper. It is by far the most consistent but it reads 0.01mm high. Mean 24.011.
• The blue line is the cheapest caliper. It reads closest to 24mm but has a tendency to read 0.01mm low. Mean 23.997.
• The yellow line is the £30 caliper. It's not quite as consistent as the blue line and reads slightly lower too. Mean 23.987.
• The green line is the worst performer. It's the £10 DIY store caliper. Mean 24.015 but notice that wavy line which is not good.

The surprise is just how good the £4.99 caliper bought from Lidl is.

I actually took four sets of measurement for each caliper:

1. 24mm measured using half the jaw depth
2. 6mm measured using half the jaw depth
3. 24mm measured with the jaw tips
4. 6mm measured with the jaw tips

Measuring with jaw tips only looks to be less accurate and it also seems as if measurements taken at 6mm are more accurate than those taken 24mm. I haven't done the graphs yet but will post them later if they're interesting enough. It would be nice to see the expensive caliper measuring equally well across the range whilst the cheaper ones don't.

+1 for everyone using micrometers for accurate work!

Cheers,

Dave

It helps to have realistic expectations when testing calipers:

http://www.mitutoyo.co.uk/hometabs/top-rated/500-196-30

Only the green one is outside the Mitutoyo +/- 0.02mm spec on that graph.

Neil

[Matthew ReedParticipant @matthewreed92137]

Interesting though this discussion is, there are aspects being missed, I think….

First there is no such thing as real accuracy. You can go on getting finer and finer measurements until you are counting atoms, and then it goes all quantum. When we get to .01mm measurements what we are really seeking is matching components, which is about fit and tolerance. Any of these devices will do this as long as we use the same device in the same way on each.

Second thought: I was always taught that the only purpose of the last digit is to interpret the previous one, so we can understand how it is rounded, and by how much. A digital calliper reading 1.00mm could be rounding up .99 which is probably good, but might be rounding up 0.901, since some electronics only measure the passing of a certain point. We instinctively round up on .5, but electronics need more instruction than that. Good kit will measure to two decimal places more than it will tell you, in order to compute the best answer it can – that might be what the more expensive tools are doing (but probably more scientific tools). When we use analogue equipment, our eyes are doing this for us whether on a micrometer or a 6" ruler.

Third thought: what we pay more for is probably quality control. Expensive kit should be more reliably accurate to the appropriate level: replicable and repeatable ( although still within a range of accuracies). They should also be more reliable mechanically. On the other hand, some of the pound shop devices will be accurate enough for NASA, but not many. When you pay more, you are probably paying for the ones they through away because they don't meet the standard.

Finally..is a 'however'….. it is common to see things that look identical at a wide range of prices. They may not be the same, having higher spec or tolerances that aren't obvious, but the nagging feeling is that they are the same. Try looking for Wigglers and you will see anything from under a fiver to over £40, in many cases using exactly the same photograph. How do we know that the £30 calliper isn't just a £5 calliper with good PR?

Edited By Matthew Reed on 27/09/2016 20:56:41

Edited By Matthew Reed on 27/09/2016 20:57:36

[SillyOldDufferModerator @sillyoldduffer]

Posted by Neil Wyatt on 27/09/2016 19:59:28:

Posted by SillyOldDuffer on 27/09/2016 16:19:01:

…

It helps to have realistic expectations when testing calipers:

http://www.mitutoyo.co.uk/hometabs/top-rated/500-196-30

Only the green one is outside the Mitutoyo +/- 0.02mm spec on that graph.

Neil

I wonder if a Mitutoyo in practice would comfortably be within spec across the range? It's possible that their ±0.02mm claim is conservative and actual performance is better.

I'm too mean to buy a Mitutoyo out of curiosity. Are there any Mitutoyo owners out there prepared to test their Caliper as I have and share the results?

Thus far I'm concluding that cheap digital calipers are better value for money than dear ones in a home workshop.

But I don't think this means that expensive calipers are a complete waste of money. My £50 example is smooth and comfortable to use. It feels good. I suspect that it, and other quality types, are likely to have longer working lives (David Cambridge apart), and be less likely to inconveniently conk out in a busy industrial setting.

Proving that expensive calipers last longer than cheap ones is too difficult for me.

Looking forward to seeing your ME article.

Dave

[Neil WyattModerator @neilwyatt]

My article will include a Mitutoyo test certificate with internal and external results, but you will have to wait five weeks

N.

[SillyOldDufferModerator @sillyoldduffer]

Posted by Matthew Reed on 27/09/2016 20:55:47:

…

Finally..is a 'however'….. it is common to see things that look identical at a wide range of prices. They may not be the same, having higher spec or tolerances that aren't obvious, but the nagging feeling is that they are the same. Try looking for Wigglers and you will see anything from under a fiver to over £40, in many cases using exactly the same photograph. How do we know that the £30 calliper isn't just a £5 calliper with good PR?

Edited By Matthew Reed on 27/09/2016 20:56:41

Edited By Matthew Reed on 27/09/2016 20:57:36

I agree. Seems to me there are two bad mistakes you can make when spending money:

• Wasting it by buying too cheap
• Wasting it by buying on reputation only or because it's "reassuringly expensive".

Wigglers are a cracking example of something I suspect to be overpriced. Unless I'm doing something wrong a dress-makers pin with a blob of Plasticine out-performs my shop-bought metal example.

How do we know that the £30 calliper isn't just a £5 calliper with good PR? We don't. Unless someone already knows, the only way to find out is to test a lot of them.

Dave

[Neil LickfoldParticipant @neillickfold44316]

On larger calipers of repute, they will give you a formula to calculate the error due to temp of the part being measured and the error of the instrument itself at different intervals or lengths. We call calipers very nearly there's. If you are within 0.02mm that is about right. If a 100 mm gauge block shows to be either longer than 100.01 or shorter than 99.99 mm , either the temp range is way off, the instrument is junk or you are not operating it correctly. Some come with a sprung slider that allows the user to use a fairly constant pressure when taking measurements and setting the reference zero. A ball bearing race is a good easy way of checking for outside comparison dimensions and inside diameter comparisons. Of course if you are after precision, you would not be using a caliper anyway. I have had a really good run from Mitutoyo digital calipers and also with the cheaper Insize brand 0-200 caliper that brought a couple of years ago. The Insize come with a test certificate and it conforms well to the gauge block tests I have done with the instrument. The very cheap calipers I brought quite a few years ago, are just that cheap and are ok for wood work where you do not need better than 0.1 from size. You can use a piece low stretch fishing line, wrap it around the part 10 times is a lot more accurate on straight diameters and using a rule or tape measure to get the total line length.

Neil

[Michael GilliganParticipant @michaelgilligan61133]

Posted by SillyOldDuffer on 27/09/2016 21:07:45:

Are there any Mitutoyo owners out there prepared to test their Caliper as I have and share the results?

.

Dave,

I have a Mitutoyo CD-6"B which is quite old, but well-cared-for.

I also have a set of 025.10000 Tesa optical flats **LINK**

http://www.tesatechnology.com/en-gb/products/optical-flats-with-two-parallel-faces-p111.htm?redirect=1&c=fr#.V-uSvet4WrU

No.1 in this set is specified at 12mm [ish]

The calliper consistently reads 12.00mm

Q.E.D.

MichaelG.

[Neil WyattModerator @neilwyatt]

Suffice to say for now that the Mitutoyo Absolute reads 25.00 consistently on my test bar.

Neil

[AjohnwParticipant @ajohnw51620]

I think Mitutoyo specify repeatability and accuracy. From memory accuracy is +/- 0.02 and repeatability 0.01mm. The repeatability is probably the usual digital +/- 1 count which is unavoidable. The 0.02 will in part relate to the length of the scale / accuracy of the encoder.

Really in that respect that's little different to good vernier calliper, they read to 0.001 and can roughly indicate over and under.

From 10 to 30C the over all length change of a 200mm calliper is around 40um / 1 part in 5000 but they may use some alloy that has a lower coefficient than that.

Temperature in old money circa  0.0016".

John

–

Edited By Ajohnw on 28/09/2016 13:18:18

[AjohnwParticipant @ajohnw51620]

It's interesting to see the anthropic principle applied to measurement again. It's easy to read an imperial vernier scale. King Henry's thumb again and a mm being too small.

Parallax? I read them square on – when I used to use them. I have switched back a vernier height gauge now so will be using them more. It lacks a flip over magnifier but a loupe or glass is easy to use.

John

–

[Howard LewisParticipant @howardlewis46836]

Interesting reading.

Total agreement with controlling temperature of "standard" and of the measuring device, and the importance of consistency in pressure applied /feel.

(Otherwise, why do large companies spend a lot of money on temperature and humidity controlled rooms for checking the accuracy of their measuring instruments?)

My practice with any measuring device is to wipe the jaws/anvils and check that Zero IS the reading, before taking each measurement. With callipers, I try to measure away from the tip, to minimise any effect of deflection. (My measuring kit, even the cheap LIDL digital calliper, is probably more accurate than my handiwork). I just look for consistency, and expect more from a dial or vernier calliper, and a reputable micrometer than from a DRO.

Strangely, this week, the DRO on the tailstock of my lathe began behaving erratically. Removing the battey and refitting after a delay did not work. Stripping and cleaning the slideways was no more effective, especially when it "froze"on 000.0. Having nothing to lose, I plucked up courage and removed the PCB and the Buttons. On the Zero area of the PCB was one speck of dirt. Once wiped off, and with everything reassembled, it seems to work satisfactorily, again.

Being a fully paid up Luddite, DROs are convenient, but mechanical devices inspire more confidence!

Howard

[SillyOldDufferModerator @sillyoldduffer]

Posted by Michael Gilligan on 28/09/2016 11:07:56:

Posted by SillyOldDuffer on 27/09/2016 21:07:45:

Are there any Mitutoyo owners out there prepared to test their Caliper as I have and share the results?

.

Dave,

I have a Mitutoyo CD-6"B which is quite old, but well-cared-for.

I also have a set of 025.10000 Tesa optical flats **LINK**

http://www.tesatechnology.com/en-gb/products/optical-flats-with-two-parallel-faces-p111.htm?redirect=1&c=fr#.V-uSvet4WrU

No.1 in this set is specified at 12mm [ish]

The calliper consistently reads 12.00mm

Q.E.D.

MichaelG.

QED? Certainly not. I'm afraid you'll have to lend me your Mitutoyo and Optical Flats so that I can re-run the tests under the same experimental conditions in my secret underground laboratory.

Obviously you can trust me to return your desirable goodies. Eventually …

Dave

[Michael GilliganParticipant @michaelgilligan61133]

Posted by SillyOldDuffer on 28/09/2016 16:54:26:

QED? Certainly not. I'm afraid you'll have to lend me your Mitutoyo and Optical Flats so that I can re-run the tests under the same experimental conditions in my secret underground laboratory.

Obviously you can trust me to return your desirable goodies. Eventually …

Dave

.

Nice try, Dave

MichaelG.

[3dtech techParticipant @3dtechtech23360]

thanks for this information.

3d printing india

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