Calipers - Dial v digital

Does anybody know where to get a small (less than 6" traditional vernier i.e., without the battery or the dial?

I bought a not so cheap digital version a few years ago and it went into the bin quite quickly - completely unreliable. I have exactly the same issue as Duncan i.e., trying to access a component under a milling machine.

My 40 year old Rabone and Chesterman is still going strong but it is just a little bit too long.

Phil H

Also useful if you can't see the display and need to move the jaws to get the caliper out - I've only had to do this a couple of times but very useful. Had to take a measurement in a blind spot so when calipers were 'on' the spot, press the zero button; you can then move the jaws as much as you like. When the caliper is out in a readable location, close the jaws together and the display will show the measurement, albeit with a leading minus sign. Just don't forget to re-zero properly before using again!

Dave

I have to say I've never thought of that one. Quick, send it in as a Tip you may get a prize out of Niel.

regards Martin

There's a bunch of factors that reduce accuracy and precision when you get into the detail. First you have to know what you have and compare like with like. For example:

• Dial types are typically ±0.02mm but many are ±0.05mm.
• Digitals are also typically ±0.02mm but some are ±0.01mm and a few ±0.005mm.

So any digital will outperform a ±0.05mm dial type, and the best digitals outperform the best dials. However, I bet most of us own calipers only good to ±0.02mm irrespective of whether it has a dial or a digital readout.

Awkward questions arise about any caliper's claim to accuracy as soon as you look at the detail. Do you ensure that the object and the caliper are both at the same temperature before taking measurements? Do you wear gloves when handling the caliper? Both digital and dial caliper are vulnerable to dirt, dial mechanisms particularly so: is the instrument clean? How repeatable are measurements? Is the instrument accurate over it's full scale or just in one place? Does it have an up-to-date Calibration certificate? If you don't have an up-to-date calibration certificate, a long list of problems may be hidden under the bonnet. Wear, bent jaws, loose gibs, skipping teeth, or other damage may be making the instrument untrustworthy.

Digital and analogue displays are both imperfect. A fault of the digital display on a ±0.02mm caliper is that it implies an accuracy of 0.01mm, which is a big fib. The faults of the dial display are that it's subject to mechanical and parallax errors plus a dial can be misread ± whole units at the revolution level, ie 10.05 read as 11.05mm

Worst of all is operator error. Not everyone is good at measuring! Getting the jaws aligned on the object isn't always easy. The pressure applied by the operator is both critical and difficult to judge. Too little and the reading will be low. Too much pressure and the caliper will bend.  Soft objects like plastics may deform.

One thing that makes me chuckle is chaps on YouTube 'proving' that their calipers are better than another make by checking a gauge block. The problem is operator bias. If you know the correct answer in advance, expect to get the answer you expected rather than the truth. As operator bias is usually subconscious rather than dishonest, nothing is proved by this type of testing. If you really want to know how good you and your instrument are, measure the dimensions of unknown objects handed to you randomly by a third party. Some who do this will be pleasantly surprised, most will be moderately disappointed, and a few horrified.

Like as not in the typical workshop both types are 'good enough' in the right hands. I say use whichever you prefer.

Dave

Edited By SillyOldDuffer on 26/10/2017 13:42:15

Oxford and Kennedy both do 5" mm/thou vernier calipers but things seem to get weirder as they get smaller.

Axminster list a 100mm Vernier caliper. Unfortunately, like their 100mm steel rule, it is metric only How much money does it actually save them to give it only one scale? **LINK** M&Ws 70mm caliper similarly is metric only. **LINK**

Farnell list a Hitec 100mm caliper, but the imperial side is in 1/128" - I'm not sure I could cope with that! **LINK**

Brian

If that fails it only takes a few minutes to dismantle the reading head and clean the PCB that slides on the scale. Small bits of swarf can get trapped between the tracks. I find a fibreglass pen brush ideal for such jobs.

Russell

Well, I checked the battery, almost full, adjusted the positive battery contact so it pushed harder against the battery, cleaned the bar with meths (or rather the French equivalent which doesn't have the blue dye in it) and adjusted the two 'gib strip' type wee screws on the top so it slides smoothly with next to no play.

Cheapo must have heard me threatening it with the bin because it's now behaving itself again, but I think I will take Peter's advice in time and get a good dial caliper too.

Peter makes a good point as to the accuracy of the digital calipers in general, I have noticed that there is often a wee bit of variance there compared to the reading on the mic and I tend to believe what the mic is telling me first, especially as whenever the zero is checked on the digital it is often 0.0005-0.001" out after a slide or two up and down the scale. But it was a cheapo!

Chris

+1 for cleaning a misbehaving digital calliper. Sometrimes just wiping the scale with a clean cloth will suffice, at worst a deeper strip down and wip;e has always sufficed. Mine is years old, from Lidl, and gets used more than either the M & W digital, or the Mitutoyo dial one. Resaon? Sheer idleness on my part.

But if it ain't broke, don't fix it!

Howard

Adjusting the gibs (all but the cheapest have a gib) can help with inconsistent zeroing.

> meths (or rather the French equivalent which doesn't have the blue dye in it)

Eau de vie?

Alcool à brûler from any supermarket in France. Keep the eau de vie for drinking

Russell

Non - c'est "Alcool à brûler".

Cheap as chips in most French supermarkets, about 7-8 euros for 5 litres, the winos over there can buy reasonable supermarket plonk for about 2 euros a bottle so presumably there is no need to make it unpleasant and dyed so winos won't drink it, not like over here!

Chris

Russel beat me to it!

Edited By ChrisH on 26/10/2017 19:05:25

Il semblait que 'ceci n'est pas une blague...'

My answer to the original question would be neither. I prefer to use micrometers, external, and internal, where possible. I have two vernier calipers, a 150mm Mitutoyo and a 600mm Fowler. As an aside neither will actually measure the headline number. I use the Mitutoyo mostly for quick measurement of parts when I am creating 3D CAD models. The Fowler gets used for larger parts, over 450mm where my micrometers run out, and a tape measure doesn't quite cut it. It might be a personal thing, but I don't find vernier calipers particularly easy to use. It is difficult to ensure that readings are taken perpendicular, especial for hole measurement.

Andrew

Neil - quite!

Andrew - I agree, much prefer to use micrometers myself, maybe it is an age thing (I was taught on micrometers in imperial not calipers in metric) but I also seem to find them more accurate, and always use them when I am chasing thous in preference to calipers; calipers just get used in the sequence tape measure - steel rule - calipers - micrometers as I get to final size, but thats just my way of working.

Chris

Not an age or metric thing. It's because micrometers are more accurate than calipers. They feature:

• A simple reliable working principle
• A highly accurate ground thread
• A stiff U frame that's difficult to bend whilst taking measurements
• Heat proof pads on the frame to minimise temperature changes due to handling. (Usually)
• A ratchet/torque mechanism to ensure that the user applies the right pressure
• Flat anvils that are easier to keep straight on the object being measured than knife jaws

The downside is that micrometers are far more specialised than a caliper, not a direct alternative. Although calipers are inherently less accurate than a micrometer, they can be used for a wider range of measuring tasks. A caliper can measure inside and outside diameters, and depths, and it does so over greater distances than a micrometer. The price paid for the caliper's extra utility is reduced accuracy. As you say, tape/rule/caliper/micrometer. Exactly right. Each has it's place and limitations. Buy all of 'em!

Dave

Micrometer comes into its own when you a making something to fit a precision part blind.

If I want a shaft to be a tight fit in a hole, I use the hole as a gauge if at all possible, and a vernier is good enough for creeping up on size. This especially true if I made the hole, as even using bore gauges or my bore micrometer I am not 100% confident of measuring the size spot on.

Neil

Edited By Neil Wyatt on 27/10/2017 16:49:45

Ah yes, but I've also got a depth micrometer covering 1" to 12" and internal micrometers from 1" to 32". The internal micrometers are not easy to use, but easier than calipers. You can never have too many micrometers; get with the groove (micrometer).

For hole/shaft combinations I usually make the parts separately, sometimes weeks or months apart, and expect them to fit together. Shafts are checked with a micrometer, and for holes I grind a plug gauge, where it is easy to tweak the odd tenth or two.

Andrew

Dave,

I was always taught (by more than one) to avoid using the ratchet/ torque mechanism on a micrometer because it was unreliable. In addition, it is very difficult to hold the micrometer properly and use the ratchet.

Phil H

Dial or digital - neither.

Quality vernier calipers. As long as your eyesight is still half decent....

Whereas I was told to always use the ratchet to ensure a repeatable torque....and I do so without any problems in use... but each to their own...

Regards,

IanT