Digital callipers.

[Inspector]

Hi Gerry
Can you explain why that is so please?
I thought resolution referred to the the smallest step that could be resolved which for these is per the 0.1mm graduations on the dial as the instrument measures continually (i.e. the dial doesn’t jump in 0.4mm increments)
I think in the link RS quote 0.4mm accuracy, although in practice they (or the ones I have at any rate) are very much better than that, I wonder if it should be 0.04mm.

Like everything in industry there are standards you do things to. Part of our job as inspectors in the aerospace machining plant was to calibrate the measuring tools used to make and inspect the parts with. We had our own procedures for calibration and the acceptance/rejection criteria was part of that. At one time some of it was based on an old US military specification which was superseded but the vernier calipers were acceptable (forgive me if I am off a touch as it has been a couple decades since reading it) if they read within +/- 0.001" for the first inch and were allowed an additional 0.003" total for up to 6" and then 0.001" for each inch of length after. So a 6" caliper could read 0.004" and still be within calibration and acceptable. You have to also understand that calipers are considered a coarse measuring tool in a machine shop and only used for rough or loosely tolerance work. If you were at the upper or lower end of the readings you went to better tools for acceptance or rejection. Micrometers are used when accuracy is demanded. What you shouldn't confuse is the resolution on the instrument as being the accuracy. The digital readout may be capable of displaying to 3 or more decimal places but that doesn't mean it is accurately measuring it. For pretty much everything you are going to do in a home wood shop they are more than good enough so don't loose sleep over it.

Pete

 

[Spectric]

If you now add in temperature and humidity then the wood may change dimensionally more than the accuracy you think you want.

 

[Jacob]

.......What you shouldn't confuse is the resolution on the instrument as being the accuracy. The digital readout may be capable of displaying to 3 or more decimal places but that doesn't mean it is accurately measuring it. For pretty much everything you are going to do in a home wood shop they are more than good enough so don't loose sleep over it.

Well yes and in any case it's most likely that a woodworker would be concerned about things showing the same rather than an accurate measurement (e.g. after passing through a thicknesser) they could all be out by 0.5 mm but fine as long as they are all coming out the same.

 

[HamsterJam]

Like everything in industry there are standards you do things to. Part of our job as inspectors in the aerospace machining plant was to calibrate the measuring tools used to make and inspect the parts with. We had our own procedures for calibration and the acceptance/rejection criteria was part of that. At one time some of it was based on an old US military specification which was superseded but the vernier calipers were acceptable (forgive me if I am off a touch as it has been a couple decades since reading it) if they read within +/- 0.001" for the first inch and were allowed an additional 0.003" total for up to 6" and then 0.001" for each inch of length after. So a 6" caliper could read 0.004" and still be within calibration and acceptable. You have to also understand that calipers are considered a coarse measuring tool in a machine shop and only used for rough or loosely tolerance work. If you were at the upper or lower end of the readings you went to better tools for acceptance or rejection. Micrometers are used when accuracy is demanded. What you shouldn't confuse is the resolution on the instrument as being the accuracy. The digital readout may be capable of displaying to 3 or more decimal places but that doesn't mean it is accurately measuring it. For pretty much everything you are going to do in a home wood shop they are more than good enough so don't loose sleep over it.

Pete

thanks Inspector.
on reflection RS are quoting 0.4mm accuracy but rather naughtily don’t qualify it.
If it is 0.4mm per mm then that’s a 40% error (or maybe 20% if it is read as plus/minus 0.2mm). Either way the instrument would not be very good.
However if it is out by 0.4mm over the max 150mm range, then thats 0.27% error which is really very good and more than I’d expect for £15, even better if it is plus minus 0.2mm in 150mm As that’s only 0.133% error.
Unfortunately, I don’t have access to a suitable set of standards to check it against So I guess we’ll never know.
What I do know is they are good enough for what I do and I have never suffered flat batteries

 

[Gerry]

The resolution or accuracy as you call it is at any point in the instruments measuring range. So if you measure something at 33.5mm on the dial it should be within the range 33.1 - 33.9mm. Usually it's well within the resolution. Other factors that need to be taken into consideration are repeatability and precision but that's a whole other ***** storm.

Gerry

 

[Fergie 307]

You know what they say, If the price seems too good to be true, it probably is and yes there are a lot of fakes out, infact there are now fakes of almost everything but surely no one is going to think they are getting the real Mitutoyo callipers for £35 or are people becoming that gullable, do these ebay sellers actually sell them? When you look at all the adverts around then you can only come to one conclusion, the human race is becoming either more stupid or living in a fantasy world.

I ordered a cheap finger type dti quite recently, no name on the dial in the pictures on e bay. I think it was about £20. When it turned up I was surprised to see the dial had Mitutoyo on it, in a quite passable imitation of the real thing. It is actually pretty accurate, but nothing like as well made or finished as the real one I have. If you want to be sure then for new ones just go to their website and find an authorised dealer. Second hand is more difficult, but look for the original paperwork, calibration certificate etc, and case. These are often absent from the fakes, or very poorly done.

 

[Fergie 307]

If you now add in temperature and humidity then the wood may change dimensionally more than the accuracy you think you want.

Also applies to metal. If you take your measurement straight after the cut when the piece is still hot from machining, then it's going to be smaller when it cools back to normal temperature. Enough to mess up if you are looking for a really accurate size. I tend to use the caliper to get down to within a tenth of a mm, then switch to a micrometer if it needs to be more accurate than that. A great example was Guy Martin's Spitfire programme. He was so proud of the precision ground pins he had made for the wings he went round showing them to everyone. Then found they wouldn't fit in the holes. The reason was that they were such a precise fit that simply holding them in his hand had caused them to heat up and expand oversize. A cup of tea while they cooled on the bench and in they went.

 

[Fergie 307]

Why use battery operated callipers at all. I've had a cheap Draper vernier calliper for about 40 years which is spot on accurate every time. It measures down to 0.1mm or 1/128 inches.
Have a posher version which is more precise which I tend not to use, not needing "thous" etc.
Maybe people don't know how to use the vernier scale? It's certainly not obvious if someone hasn't shown you how to do it.

Couldn't agree more, I use mine all the time. Often just lock them at the relevant size and use as a pass/no pass when on the lathe. I think you are right though in that a lot of people don't know, and sadly don't seem to be taught, how to read the scales. I don't tend to use them to their proper potential anymore, but only because my eyesight is no longer what it was and the digi ones are easier to read.

 

[Spectric]

Also applies to metal.

But if you buy a length of 40mm box section that is 2 metres long it may change length very slightly with temperature and rust due to humidity but at least it will not twist or warp on it's own accord ! This has been one of my biggest headaches when dealing with wood having always been into metalwork before.

 

[HamsterJam]

Just a thought for those with digital callipers and poor battery life…
Are you actually switching them off after use?
Poor battery life of the Trend DAR was discussed on here a few months ago. The display turns off after a few mins or if you briefly press the off button. If left like this they eat batteries. Pressing and holding the off button down for a few seconds turns them off proper and in this mode the batteries last ages.

 

[Richard_C]

I used the vernier type for years, but with ageing eyesight/varifocal wearing I got myself a cheapo digital calliper from Maplin (remember them?) a few years ago. Plenty accurate enough for woodworking and teh other diy things I do. The display comes to life whan you start to use them regardless of the on/off button which made me think there is always something running in background - I take the battery out when I put them away and it lasts a lot better.

Having read the post above, I will try the press-and-hold on the oiff button. Good thought.

Anyway, I seem to have upset them by measuring the thickness of some very powrful magnets so was looking around for a new set. I came accross some on ebay for £2 something - wouldn't buy them but the blurb described them as "the perfect gift for your lover, friends or family". It seems likely that English isn't the author's first language, but I hope I never have a lover who feels the need to check any part of me with a digital calliper

 

[Jonm]

I bought some very cheap 150mm digital callipers about 4 months ago, basically because I wanted something I could read easily without putting my glasses on. Cost was £4.95 inc vat and postage, from eBay, uk seller, arrived within a few days.

Jaws were not completely parallel, could see light in places between them when they were touching, so I carefully filed the plastic a bit, got them better but not perfect. Had to do a bit of filing on the depth measuring part as well.

I have checked it for accuracy using drill bits up to 12mm diameter. It is accurate to between 0.0mm and -0.2mm. In other words if I measure a drill bit between 3.3mm and 3.5mm then it is a 3.5mm drill. Unless I have picked up an imperial one.

I am very pleased with it, measuring timber dimensions and sizing drill bits it is a lot more accurate than a tape measure and easier to use especially if I do not have my glasses on. I normally work without my glasses on and only use them for close up when I need them.

Edit - I had another look at accuracy. Measured some feeler gauges 0.1mm to 0.5 mm in 0.1mm steps. Callipers measured them all spot on. Then tried a piece of metal, digital calliper 49.5mm, Rabone and Chesterman, traditional vernier calliper measure 49.44mm. So it appears that the callipers are more accurate than I stated above. The gap in the jaws I mentioned above is less than 0.05mm. The digital readout is to one decimal place.

 

[ey_tony]

Am I just unlucky or am I buying to cheap.
I will soon be in the market to have to buy my third set of digital callipers. I’ve spent between 20 and 30 pounds at different times. I’ve had the last set for about 2 years.. looked after them and returned to their cases after use. On both set they will not hold the readings. Have eliminated battery connection problems, new batteries etc. They just give wrong or different readings. In short I just dont Trust them.
Do I need to spend more money or just buy cheap and don’t expect longevity?View attachment 112022

I can only speak as I find.
I have set of Workzone (ALDI ) in front of me now which cost less than a tenner and I've been using them regularly for the past 5 year and I still trust their accuracy or at least trust them as much as I would with any other similar set of calipers.

I've tested their accuracy with two sets of decent engineering quality micrometers which I own and they read pretty close, certainly close enough to rely upon their accuracy in most situations. If I was perhaps an engineer working ot tolerances of thousandths of an inch or the likes where every thou was critical then my views might change but for everyday work, they are more than accurate and adequate for what I need.

I'm always using them wherever I can as these days they are more precise than my eyes and a rule and in the time I've owned them, I've only replaced the battery twice I believe.

 

[Paddy Roxburgh]

FWIW I always use dial calipers. I find the vernier scale hard to read without my glasses (and lord knows where I put them down), and unlike digi ones, the battery never goes flat.
I have a mitutoyo pair, but tbh a cheaper pair would probably be fine.

 

[stuart little]

I've been using Workzone digi. calipers for years, I take out the battery when not in use & they last for ages. I keep one in my workshop & one indoors in my hobby desk. The only problem is of my own making, managing to drip CA glue on the display cover which eventually obscures the readout. I've just bought a couple of 'carbon fibre' ones off ebay for £3.99 & 4.95 with bats.! Good enough for model shipbuilding. I use a M & W for more accurate work. The PCBs for digital calipers are probably all made in the same factory in China. Just like TV's, all circuit boards (mother boards?) made in one factory then distributed to the 'manufacturer' to be built into THEIR own carcases & fittings. I was passed this info by a very experienced TV engineer who cut his teeth when TV's WERE repairable, or worth repairing.
Unless someone knows better.

 

[REN]

Thank you all for your thoughts, experiences with digital callipers. Most useful. Both high and cheaper prices seem to have merit. One thing I will take away and err to in the future is to take batteries out after a woodworking sesh. Often thought in the past that my batteries always seemed to need replacing. Always bought cheap replacement types. I will try pukka silver oxide types as well. As I often shop at Lidl I might give them a try. Any extra cash saved I will spend at British Hardwoods on maybe a nice piece of walnut.

 

[Renoman]

I can only speak as I find.
I have set of Workzone (ALDI ) in front of me now which cost less than a tenner and I've been using them regularly for the past 5 year and I still trust their accuracy or at least trust them as much as I would with any other similar set of calipers.

I've tested their accuracy with two sets of decent engineering quality micrometers which I own and they read pretty close, certainly close enough to rely upon their accuracy in most situations. If I was perhaps an engineer working ot tolerances of thousandths of an inch or the likes where every thou was critical then my views might change but for everyday work, they are more than accurate and adequate for what I need.

I'm always using them wherever I can as these days they are more precise than my eyes and a rule and in the time I've owned them, I've only replaced the battery twice I believe.

I have the same. Very pleased with them. I do however remove the battery when stored.

 

[pe2dave]

Sharing a concern mentioned: A recent addition to my 'toolkit'. A 6x magnification glass, right in front of the workbench, i.e. in easy reach. Most essential. ;-)

 

[ey_tony]

I have the same. Very pleased with them. I do however remove the battery when stored.

You really can't go wrong with a set of those. As long as they are checked on occasions with a known measurement via micrometer or the likes just to be sure they're still reading accurately, they're a really good investment. I do the same with the battery, take it out and put in that little pocket but they do naturally fade over time.

In the same vein I also have a Powerfix (LIDL) digital angle gauge which I use very regularly which together with a sliding bevel, accurate angles are a doddle. It's good for both internal and external angles and a little tool I wouldn't choose to be without.

 

[MorrisWoodman12]

I bought a pair of DML calipers a couple of years ago. Seem to be OK but I have to watch out for the battery running low especially in cold weather as the reading becomes inaccuract. The other thing is that although you can turn them off you only have to nudge them and it turns back on so I have to clamp them when I turn them off. Just tried the hold the off button trick mentioned above: it doesn't work for me.