Comments on: How acurate is acurate? Digital calipers versus ‘old’ micrometers!

By: Bill

Bill — Thu, 12 Jan 2012 07:31:59 +0000

One other thing, the digital calipers you show in the picture all seem to be (no offense intended) the “bottom of the barrel” Chinese made calipers. There’s a reason people pay more for Mitituyo, Brown & Sharpe, etc. You would be much better off with a Mitituyo dial caliper (non-digital) than with the digital ones you are using. They can be picked up off Ebay pretty reasonably as they’re not as popular these days.

People often confuse “digital” with “accurate”, there’s no particular relationship between the two. Invest in some good quality equipment. Calipers are generally thought of as convenient but not particularly accurate. If you need accurate use micrometers. Once you have a good micrometer you can figure out whether your calipers are accurate or not, and if not what the error is and whether you can just correct for it.

Shop Ebay, don’t be in a hurry and you’ll be amazed at what you can buy. Last weekend I picked up some Brown & Sharpe #1 mikes, about as high quality as can be found, made by Etalon in Switzerland, for $25 each in like new condition. They’re probably $250 each new, well out of my price range. Invest in quality measuring tools, they’ll last the rest of your life and your kids’ if you take care of them.

By: Karl Fenn

Karl Fenn — Tue, 03 Jan 2012 00:05:44 +0000

The article on the digital calipers was interesting to me, l tried similar experiments
with electronic calipers and found identical results, l made sure all the instruments
were perfectly clean, and measurements all done under the same tempreture, as it
can effect measurement, l noted that in the main the measurements were o.o1 to o.o4
out on the same item being measured, l did not use cheap calipers mine where quiet
high quality, my older manual steel caliper was the most accurate, the moral or the
story must be, electronic calipers and micrometers still have room for improvement,
l must say l no longer use the electronic ones for crucial measurements.

By: Malachy Doyle

Malachy Doyle — Fri, 21 Oct 2011 20:24:14 +0000

As a time served Toolmaker involved in high precision presstools and injection moulds I would advise the purchase of a quality long travel dial indicator with a few different point attachments. It may take a while to feel comfortable with the indicator but it is worthwhile. My reasons for saying this is that the dial indicator eliminates operator-touch-and-feel errors, so accuracy is repeatable as opposed to hit and miss. In other words the readings will be precise with no ifs and buts.

By: Mike Freeman

Mike Freeman — Wed, 25 May 2011 13:21:06 +0000

Thanks Paul,

Good advice, from a hobbyist rather than a professionals view you can buy professional quality second hand equipment. I have bought micrometers of all types from Ebay and I would sooner use a second hand micrometer than a new (and often much dearer!) digital caliper. That said for many jobs (especially conversion between metric and imperial) then digital calipers have an important place. As the old saying goes its ….horses for courses…..

By: Paul

Paul — Wed, 25 May 2011 08:38:38 +0000

Just a few things,

I have been working in in the metal trade for 32yrs and I generaly work within tolorances of 0.001mm and have to use both micrometers and digital verniers,here is my veiw,

1-ALLWAYS use a micrometer if posable but check both min & max WITH A MIC GUAGE! If your mic is old and has been used more at one end than the other then there will be a slight diferance and ajust.

2-Digital calipers are great and easy to use BUT!!!!! It depends on who uses them and funny thing, on there mood!!
even the same person will get a variation of readings and that is with a new set.

3-With an old set of digital calipers there will be worn parts that have to be taken in to account- The out side jaws will be accurate at the base but will generaly be out any where from 0.001mm to 0.2mm at the tip depending on who has used them and how worn they are not how old, With the inside jaws the same aplies.

4-To summerise Use a micrometer if posable.
Digital verniers are good but use a mic guage to test or
set and use as a comparitor ie: set or test your calipers at the part of the jaws that you are going to use.

5-Invest in some good quality outside & inside Micrometers
and only use your verniers where these can’t be used and you can’t go wrong.

By: mark

mark — Tue, 02 Nov 2010 06:08:23 +0000

just my two cents
I have been a mackinits for 32 years and work onlarge parts now 500 to 2500 lbs holding tolerances between .0003 to .002 in daily we use mic’s for up to 15 -16 in but the cost of mics for up to 36 in in 1 inch increments was probhibitive (sp) I guess because we use old vernier calipers and some digitals the digitals will almost always read .001 to .002 smaller than the mics but you can set zero anywhere you want so if the are gauged to be small at all reading then just set them small at 0 but i question how oftenare you really holding .001 and at what dia’s if its under 1.0 or 2.0 inches i would suggest mics for the fin size and clipers for getting close before final sizing they are faster but not much can match a good set of mics.

By: Peter G. Shaw

Peter G. Shaw — Sat, 28 Nov 2009 21:55:15 +0000

Just another thought. In Mikes picture well above, he shows an Axminster digital caliper reading 0.597″ and which appears to be the lowest reading. Ironically, the design of the caliper, ie the display unit and the shaft or bar decoration is exactly the same as my Rolson which also reads low! Perhaps there is something here, possibly even made in the same factory etc.

Regards,

Peter G. Shaw

By: Peter G. Shaw

Peter G. Shaw — Sat, 28 Nov 2009 17:12:34 +0000

Just a further thought.

I have a friend who is a retired tool room engineer and who has a micrometer with a vernier scale thus reading to “tenths”. On comparing readings from my micrometers (no vernier scales) and estimating in between graduations, I was very gratified to discover that I could estimate almost as accurately as my friends “tenths” scale micrometer was reading. My friend said that this was quite normal in that the eye/brain combination is capable of splitting small divisions quite accurately.

Regards,

Peter G. Shaw.

By: Peter G. Shaw

Peter G. Shaw — Sat, 28 Nov 2009 17:03:23 +0000

Follow-up.

Oh dear, the formatting hasn’t worked!

Sorry, you’ll just have to transcribe them onto paper or a spreadsheet.

Regards,

Peter G. Shaw

By: Peter G. Shaw

Peter G. Shaw — Sat, 28 Nov 2009 17:01:37 +0000

I’ve now done my testing – see my posting two above.

As I said, the standards, accurate at 20°C, and the measuring instruments were left overnight in a warmish room and the tests done in the same room with a temperature of 20.9°C at the start and 20.7°C at the end. All tests were done at least twice. The measuring instruments are:

Imperial Micrometer, resolution 0.001″ – Mic 1
Metric micrometer, resolution 0.01mm – Mic 2
Vernier caliper, marked INOX (but this may just be another name for stainless steel), resolution 0.05mm – INOX
Draper dial caliper, resolution 0.02mm – Draper
Rolson digital caliper, resolution 0.01mm, accuracy 0.02mm
(0-100mm), 0.03 (100-150mm), repeatability 0.01mm – Rolson
Workzone digital caliper, resolution 0.01mm, – Workzone
Note the limited specification of the Workzone caliper.

The results are shown: Device name – reading 1/reading 2

Mic 1 – 0.9843/0.9843″ (Equivalent to 25.00122mm)
Mic 2 – 25.004/25.005
INOX – 25.00/25.00, 50.00/50.00, 75.00/75.00, 100.00/100.00, 125.00/125.05, 150.00/150.00
Draper – 25.045/25.045, 50.085/50.085, 75.087/75.082, 100.140/100.100, 125.095/125.085, 150.185/150.100
Rolson – 24.98/24.98, 49.98/49.98, 74.98/74.99, 99.99/99.98, 125.02/124.99, 149.99/150.05
Workzone – 25.03/25.04, 50.05/50.03, 75.08/75.05, 100.10/100.04, 125.00/125.00, 150.00/150.00

Comments:
The two micrometers and the Draper dial vernier were estimated by splitting the graduations.
The INOX vernier is difficult to determine which graduation to use. I suspect that some of these readings are actually between 0.00 to 0.05mm higher.
I suspect that the slight differences on the purely mechanical devices are down to varying pressure when measuring. I suspect the same will apply to the digital units, however the Rolson repeatability seems very good, albeit consistently low. Maybe I am applying too much pressure.
The Workzone device does not seem particularly consistent to me.

Well, after all that, I don’t know what to do. It does seem to me, that as an amateur making stuff for myself, that at any one time,I need to use one device only to the exclusion of the others. This does mean that the idea, as I originally intended, of using the Workzone caliper to make a digital height guage is a non-starter. This does also make me wonder just how accurate are all those lathes and milling machines fitted with digital readouts.

Regards,

Peter G. Shaw

ps. I’ve tried to set the readings as in a table. At the time of writing, I do not know how it will appear. If it’s a mess, well, sorry, I don’t know what else to do.