Tool accuracy

[rosinante]

Theres a lot of talk about digital accuracy,measuring to 0.01 mm etc,i suspect this is cos its easy with a numeric display,however there is a difference between accuracy and scale definition,a digital scale can display 0.01 mm but have an accuracy of +/- 10 % ,I would not imagine that a digital caliper from Aldi or the like will be calibrated with traceability.If however the comparison of a mortice size to a tenon is made easier for those of us with old eyes [my mum was right about going blind] go for it, my steel rule says "standard at 20C" so I had best not use in the winter,most woodwork is judged on its appearance when finished ,cant see acustomer saying it six thou too long.
Just my twopenneth
Chris

 

[Jacob]

Agree.
I don't like digital measuring much because you can never know for sure what error is involved, even if you were to calibrate it every time. It could blow a fuse (?) and be miles out. Whereas a simple conventional vernier caliper reading to say 0.1mm to is easy to read and any errors over the 0.1mm are instantly obvious.

 

[Rhossydd]

Theres a lot of talk about digital accuracy,measuring to 0.01 mm etc,i suspect this is cos its easy with a numeric display,however there is a difference between accuracy and scale definition,a digital scale can display 0.01 mm but have an accuracy of +/- 10 % ,

You make a good point that it's important to consider the accuracy of these budget tools. +/-10% of 0.01mm is probably wildly optimistic. +/- 0.01mm is probably closer to the mark, but would test the skill of the user for repeatability anyway.
The great aspect of digital measuring tools like this is that they are very easy to read, so making multiple reading is quick and simple and helps gather an appreciation of measurement error, both from user error and the inherent repeatability of the instrument.
In comparison trying to read vernier scales is much more error prone in itself.
Digital instruments usually also have a zeroing capability at any point, so you can use them just to measure variation, rather than absolute distance. Ideal for checking how well, say, a thicknesser is actually performing.

I would not imagine that a digital caliper from Aldi or the like will be calibrated with traceabilitys

No they won't have been calibrated against a world standard reference, but saying they may not be absolutely correct doesn't exclude the option that they might still be very accurate indeed. Test and check. My eBay cheapie compares very well to other vernier callipers I have around, so I've no reason not to trust it.

 

[Rhossydd]

It could blow a fuse (?) and be miles out.

'Blow a fuse' ?? joke or troll.

I don't like digital measuring much because you can never know for sure what error is involved, even if you were to calibrate it every time.

That doesn't make any sense.

 

[nanscombe]

Are digital calipers engineered to the same standards as dial callipers?

My digital calliper has a zero button on it so I probably end up zeroing (as opposed to calibrating) it every time that I, infrequently, use it. That's if the battery hasn't gone flat.

 

[bugbear]

No they won't have been calibrated against a world standard reference, but saying they may not be absolutely correct doesn't exclude the option that they might still be very accurate indeed.

Whilst proper gauge standards are expensive, an old amateur engineer's trick is use a ball bearing. Since ball bearings need to be very similar to each so that each takes an equal load they are manufactured to quite amazing tolerances, but due to the miracles of soul-less industrial mass production, they're very cheap.

http://en.wikipedia.org/wiki/Ball_%28bearing%29

They're not (technically) gauges, but they work just like one for most practical purposes.

BugBear

 

[Jacob]

It could blow a fuse (?) and be miles out.

'Blow a fuse' ?? joke or troll.

I did put an ironic question mark but you weren't sharp enough to notice so I'll explain it simply - when digital readouts go wrong they go very wrong (e.g. when batteries go flat) - not just a small percentage difference

I don't like digital measuring much because you can never know for sure what error is involved, even if you were to calibrate it every time.

That doesn't make any sense.

To you maybe not, but one can't spend all day explaining things to simpletons! :lol:

 

[Racers]

The best thing about digital gauges is they are easy to read, no chance of misreading, a far more common error than a "blown fuse"

Pete

 

[Jacob]

The best thing about digital gauges is they are easy to read, no chance of misreading, a far more common error than a "blown fuse"

Pete

Easy to read yes, but an ordinary scale also gives you a visible representation of the measure and indicates "scale of magnitude" in a simple way.

 

[Rhossydd]

when digital readouts go wrong they go very wrong (e.g. when batteries go flat)

Which is one of their strengths. You don't get mislead if there's no measurement at all.

 

[Racers]

Digital callipers also have a ordinary scale on them, so where is the problem?

I think I know...

Pete

 

[Jacob]

when digital readouts go wrong they go very wrong (e.g. when batteries go flat)

Which is one of their strengths. You don't get mislead if there's no measurement at all.

erewego explaining again! Waste of time.
When a digital readout is faulty, or the battery is nearly flat, it can give erratic readings. You don't get erratic readings with a scale, unless your hand shakes or you have double vision etc.

 

[Jacob]

Digital callipers also have a ordinary scale on them, so where is the problem?

I think I know...

Pete

The vernier part of the scale is replaced by the digital mechanism. There isn't a problem, I just prefer the direct reading from a scale, rather than the third party digital reading. You can see where you are with a scale.

 

[Rhossydd]

an ordinary scale also gives you a visible representation of the measure and indicates "scale of magnitude" in a simple way.

The discussion here is about tool accuracy, very small tolerances. There's few tools that offer an 'ordinary scale' for this sort of application. Dial gauges might fit the bill, but need more care and can be to difficult set up.

 

[Racers]

All these digital callipers have a scale on so where is the problem?

https://www.google.co.uk/search?q=digit ... 8#imgdii=_


Pete

 

[Jacob]

If you look closely Pete you will see that the vernier part is replaced by the digital component. Maybe you don't understand how a vernier caliper works. Here's a picture

 

[Racers]

If you look closely they have a scale on so you can see where you are with the scale, and read the accurate measurement of the display.

I can't see the problem Jacob, it must be all in your head.

Pete

 

[bugbear]

All these digital callipers have a scale on so where is the problem?

https://www.google.co.uk/search?q=digit ... 8#imgdii=_


Pete

Helpful diagram:

BugBear

 

[DTR]

No they won't have been calibrated against a world standard reference, but saying they may not be absolutely correct doesn't exclude the option that they might still be very accurate indeed.

Whilst proper gauge standards are expensive, an old amateur engineer's trick is use a ball bearing. Since ball bearings need to be very similar to each so that each takes an equal load they are manufactured to quite amazing tolerances, but due to the miracles of soul-less industrial mass production, they're very cheap.

http://en.wikipedia.org/wiki/Ball_%28bearing%29

They're not (technically) gauges, but they work just like one for most practical purposes.

BugBear

That's a useful tip, thanks for the info.

Disclaimer: this has no relevance to my woodbashing where I seldom measure anything, let alone work to a tolerance. It may, however, prove very useful in my engineering pursuits

 

[Jacob]

an ordinary scale also gives you a visible representation of the measure and indicates "scale of magnitude" in a simple way.

The discussion here is about tool accuracy, very small tolerances. There's few tools that offer an 'ordinary scale' for this sort of application. Dial gauges might fit the bill, but need more care and can be to difficult set up.

Ordinary non digital vernier calipers fit the bill too. The one I pictured above measures to 0.05mm. Mine does 0.02mm which is too fine for woodwork machines. I've also got a cheap Draper vernier which does to 0.1mm which is good enough, easy to read, easy to use, reliable.
Judging from some of the posts above I wonder if some people don't know how to use a vernier?
Handy gauge standard for woodwork purposes is an allen key. I just measured one - 4mm exactly to the nearest 0.02mm. They often have their size etched on, unlike a ball bearing, which you'd have to measure, leaving you with a chicken and egg dilemma!