[jcgrillo]

With a decent set of vernier calipers (I have Brown and Sharpe ones) they're accurate to 0.001" (0.02mm) every time. But what's nice about analog measuring tools is you can actually reliably achieve better accuracy--like 0.0005" +/- 0.00025"--by "reading between the lines". I can reliably take finishing cuts accurately to a few ten thousandths of an inch using vernier calipers (confirmed by checking with a micrometer accurate to 0.0001").

The only application I've encountered where digital tools work better for me is having a DRO on a mill is extremely convenient.

[varjag]

You really want to use a mike on this kind of precision. Calipers can be repeatable in a certain range but even then a readout from vernier gives too much error. Measuring a tenth of mm is acceptable (tho I'd never trust a vernier caliper measurement beyond 0.2). A hundredth IMO is wishful thinking.

[jcgrillo]

Looking at my calipers now I noticed that the imperial side is twice as precise as the metric side. Graduations of 0.05mm vs 0.001". I wonder why that is.

[bagels]

Precision, maybe, but is it accurate to that degree?

[jcgrillo]

In my experience, yes. I've checked with micrometers that are an order of magnitude more precise. You have to be fairly experienced reading it, and it often helps to use a magnifying glass. Also you have to be very careful not to drag the jaws open when removing from the object you're measuring. Taking multiple measurements and averaging helps.

To be clear, for a measurement where accuracy to less than 0.001" actually matters use a micrometer! Otherwise you're likely to screw up the part. But the advertised precision of 0.001" is totally repeatable within 0.0005".

[genewitch]

tenths and hundredths of an inch "don't mean anything" because we don't divide inches that way in common use, but in subtractive manufacturing and the like they do use "thou" - and 0.001" is a thou.

Personally, i use microns instead of 0.001mm, too, when measuring that small. I forget the accuracy of my good calipers, but i could detect errors of around 2 microns if memory serves. It's been a long time since i cared about anything that accurate so i have two pairs of cheap plastic ones - scale and digital.

[varjag]

A typical metric micrometer is accurate to 0.01mm (tho you can find more precise ones at premium). It's really unlikely you'll get a micron precision from any calipers. Even an angry glance warms up the instrument enough to make this meaningless.

Microns are the domain of grinding and lapping, you rarely ever need to go there with cutting.

[genewitch]

you're right, the 3d printer i had was accurate to "within 20 microns" which is what my decent metal calipers can measure. 20mm = 20mm within 0.02mm.

I've already started calling the fab size of my processor as 80 angstroms (or whatever), so i probably back-propagated that.

[jcgrillo]

> tenths and hundredths of an inch "don't mean anything" because we don't divide inches that way in common use

Architectural rulers tend to divide inches into tenths for some reason. I have no idea why, because lumber comes in multiples of 12 (e.g. 8', 10', 12', 16') so if you design in multiples of 10 you're likely to waste a lot. If anyone knows I'd be curious to hear about it, mostly it makes drawing things to scale a pain in my ass..

[sokoloff]

Somewhat ironically, it's to make architects' jobs easier when they're drawing things to <architectural> scale.

If you're making a floor plan drawing at 1:100, a 240 inch wall becomes 2.4 inches on the drawing. The scales [of the drawings] and the scales [the tools] evolved together. (Similar to "why do computer people work in base 2 or base 16 so often?")

[jcgrillo]

Makes sense, I'll try to work in whole number scaled inches more (although tbh I'm just being picky, eyeballing the fractional part is usually good enough).

[_Microft]

> i use microns instead of 0.001mm

What "micron" are you referring to here? The "micron" I am familiar with is exactly that one (i.e. 1 micron = 1µm = 0.001mm).

[jcgrillo]

Yeah I only use calipers and micrometers for machining--I haven found any use for additive manufacturing--and never in metric units because all my tools are imperial. Just strange the calipers punish metric users by giving them only half the precision.

[Moru]

If you buy a tool in a country that is mainly using imperial, the markings on it might be more exact for the imperial measurement. Might be the opposite in a country with metric. Just guessing though but that is often how other things work out.

[Symbiote]

A Google image search for "caliper" shows several have 0.001in and 0.02mm accuracy, which is similar.

For 0.01mm there are only electronic or dial calipers.

[nuancebydefault]

I really cannot understand that you talk about micro meter (um) accuracy on a caliper. If you apply a tiny bit more pressure or it is under a tiny angle, the error is at least tens of um.

[jcgrillo]

Try it! You might surprise yourself.

EDIT: ah, I see your confusion. A "micrometer" is an aliased term. It means both "a millionth of a meter" and "a tool for measuring very precisely". I used the latter meaning above. Although in terms of order of magnitude precision they're identical--a micrometer accurate to 0.0001" is accurate to 2.54e-6m. It's possible to get within a handful of µm with decent calipers. Easier with a micrometer.

[rowanG077]

It depends what you are measuring. Some plastic piece? Of course this has a ton of flex. A solid steel shaft? No way you can flex it tens of um.

[nuancebydefault]

You don't need to flex the material you are measuring to get tens of microns difference. Simply both sides of the caliper will not stay parallel since there is always some dust or fluid between the sliding pieces. The dust will simply flex.

[rowanG077]

Of course. To get a good reading you have to clean both surfaces. I mean if you want to wring blocks together it won't work without clean surfaces either.