Precision measuring

with regards to digital over analog and vice-versa, they are both accurate to a tolerance of +/-0.01mm. The price of any caliper normally reflects the quality of the craftsmanship so, in this case, the more expensive the better.

As you've mention Mitotoyo, this company provides highly accurate, good quality measuring equipment throughout all of their price ranges (digital). When closing their digital calipers it is of utmost importance to make sure that there is no debris or filings between the datum surfaces. If these surfaces are always clean you will find that you will very rarely have to zero the caliper (i suggest cleaning with a dry cotton rag). If debris is present when you zero the caliper you will obviously be offsetting the tolerance with an additional increment equivalent to the size of the debris present. another important factor is that the caliper should not be press shut to aggressively on the object being measured as any excessive pressure may cause inaccuracies in the spring-loaded sliding mechanism. This also goes for analog calipers.

Analog calipers do not lose their zero positions which is a great advantage but they are a pain in the a** to read, slowing down productivity while dial gauges are extremely accurate but extremely delicate as well and will require regular calibration to keep them within acceptable tolerance.

Overall, as far as which is the best caliper, them all have their pros and their cons so it's pretty much up to the individual that will be using the said instrument.

Hi ronseto,

Have you taken measurements of the same things with both your vernier and digital calipers? Comparing the two values will give you an idea of how accurate the digital version is. Concerning your digital calipers: "you get what you pay for". There are very accurate digital instruments out there; how their prices compare with like-accuracy/quality vernier instruments may be worth looking into.

Mike

A frend gave me a cheapo digital caliper. It was only something like 18$, so I wuznt expecting much. But I'v had it for 8 yirz & its alwayz been rite on.

I'v had a Starret digital caliper for 25 yirz that meajures in tenths with little barz that stack up next to the digits. It meajurez perfect with the main jawz, but haz alwayz been under by a few thouzandths with the inside & depth bar unless you set it by them.

Calibrating mikes and calipers

Ronseto -- You are likely already aware of what I'm writing below; but for some other readers the info may be helpful.

Check your measuring instruments against known standard bars or gauge blocks over their whole range. Most people use shop grade gauge blocks (grade B or the new AS-2) for micrometers and calipers. The tolerances on these gauge blocks are in the range of +/- 25-75 millionths (micro inches) in length and a lot closer in flatness and parallelism.

Keep in mind that the gauge block(s) and caliper should be at the same temperature. So you won't get a good check on a mike that you've been carrying around in your hot little hands for a while.

Chinese made shop grade gauge blocks are not all that expensive these days and are perfectly good for this purpose. If you have a contact in the machining trade it should be relatively easy to get your mikes and verniers checked for accuracy for your hobby purposes against a commercial machine shop's gauge block sets.

One way to come up with your own standards for checking your measuring tools is to get hold of old ball bearings that aren't rusty. The outside diameters and widths of the outer races are made to very close tolerances of flatness and roundness as the case might be. If you can get someone to measure the exact size for you to maybe 100 micro inches accuracy you've got a good standard. Steel dowel pins and hydraulic valve lifters are also ground to close diameter roundness tolerances as are the shanks of end mills and drills. These can be good standards for under 1 inch diameter.

Another possibility is offered by a good quality set of small machinist's 90 degree squares. These particular tools have a myriad of uses in the workshop. The widths and lengths of the arms are normally ground to close tolerances of flatness and parallelism although the lengths are not ground to special dimensions. If you have these tools in your shop and can get someone to determine the dimensions accurately then you will have a good set of standards for checking calipers especially at the large openings. Ideally chemically etch the actual dimensions as verified right on the surface of the square. If you can only do the etching mechanically use a light touch lest you distort the tool unnecessarily.

It's important to be aware of temperature effects when you are dealing with precise dimensions. You can do an instructive experiment. Once you have a good standard for a length of a few inches leave the tool and the standard together in the same place for a few hours so that they will be the same temperature. Take a measurement and write it down. Now go set either one in the sun, on a warm surface or maybe in a pocket close to your shin for a while, redo the measurement and compare it with the first measurement. Repeat the experiment with your now properly calibrated caliper and a piece of aluminum which is warmed. You may be surprised by the results.

Ed Weldon

Great idea about using ball bearings as reference standards. I have always bought the best tools, especially when it came to absolute accuracy. Unfortunately, retirement has forced me into economizing on my tool purchases. I'm buying tools from China more and more; more than I like, but the quality precision tools I still have are taken good care of. They give me great security when I need accuracy in my projects (home machinist).

Lots of good posts here, I found them all very interesting, many thanks Guys.

I have two cheap electronic verniers, one was a present, the other I bought.

I have not had a "jumping" problem with either, but there again I do not move it that quickly either.

For the accuracy achieved they were REALLY REALLY cheap!!! I have compared them against my (normal) micrometer and vernier.....no differences worth noting found!!!

They agree with each other exactly, but both need (I feel) to be zeroed before use....I do it automatically each time as I have found that removing the batteries, stops the batteries being empty when I need it!! Its the old problem of the touch sensitive contacts against real switches for on/off....if you are using it daily, its not a problem.

I also brought an electronic depth gauge (appears visually to be the same manufacturer as one of my verniers) for setting up the table of my CNC machines, so that they are exactly flat, that way the tool (kept at a constant height) cuts the same depth anywhere on the table....

It was simply too fiddly to use one of the verniers backwards for the same job......

With it I am able to set up the table to an accuracy of about 0.02mm (slightly less than 0.008"), which is the approximate limit of the flatness/roughness of the heavy duty plastic coated chipboard that I use.

Happy new year!

1. Don't ever buy cheap tools.

2. If precision is your game have one, two or more standards.

3. Don't be (like myself) an old bugger that can't adjust . The times are a changing...

Wangito

Ron, regardless of the display method used, all beam calipers must pass the same standard for repeatability and precision. The basic rule is that all caliper types must be accurate to +/-0.001" within 6". For absolute longevity the Vernier type definitely wins hands-down. The only disadvantage is its higher cost and it is not easy to read at an angle. I will add that I had cataract surgery this spring, and until I did I went through a mild version of hell each time I used them during the previous four years.

I have all types that I collected over the years. What do I prefer? For larger (say 12"/300mm) types I prefer the Vernier with the 50-division scale as it is quite easy to read. For the smaller (say 6"/150mm) type I prefer the digital type. What I like most about these units is the ability to quickly switch between inch and metric.

Also, when using a digital unit - if one has to take a measurement in an area where one cannot see the display, the measurement can be made and the caliper zeroed with the button. When the caliper is extracted so that the display is visible it can be closed and the dimension read in its negative form. Perhaps that is the best feature of these units and sometimes a lifesaver.

The vernier units can become quite dirty and still function, and be cleaned without much grief. The same can be said about the digital units; provided they do not become soaked with a conductive liquid. The dial caliper must be stored face down when working near flying chips - even if it has the rack cover. Even when they were a novelty thirty years ago I did not like them. It was too easy to damage the gear rack with a tiny chip.

I have an old 12" Helios dial with the standard deep jaws and the slender "pinching" jaws on the top. They are handy for reaching into narrow channels and I keep them as a reminder of days gone by. For my daily use I have a Mitutoyo inch/metric 12" long-jaw Vernier unit and a Starrett 6" digital unit kept near my desk - these are my workhorses. I do keep a cheap Fowler 6" digital caliper in my computer satchel.

If I intended to purchase a type that I could absolutely trust for the remains of my days - it would be the Vernier type with adjustable Vernier scales. The jaws can be repaired should they wear a bit, but with careful use mine are still quite accurate after thirty years of continuous use.

Best Regards,

Ing. Robert Forbus

Good answer! Thanks for the great tip about using the zero button to preserve a reading. ....Ed Weldon

I use several digital calipers (mostly Mitutoyo) and have them calibrated by an outside source every year for about $60.00 (SPECIAL ACCREDITED 17025 WITH UNCERTAINTIES). I have one that is nearly 30 years old, and it still reads accurately to 0.0005" (0.0125 mm) over the whole range.

They all have the problem you describe of slipping when you move them too fast, but this generally only happens when you first turn them on. As a result I always zero it twice, and then open and close the jaws a few times to be sure it always returns to a zero reading before using it.

The statement that these calipers are all accurate to +/- 0.01 mm is a bit misleading: they are generally readable to 0.01 mm, but the rated accuracy (for Mitutoyo) is +/- 0.025 mm (0.0010").

I never had to replace the battery on my vernier calipers.