How Accurate Are Low Cost Digital Calliper Micrometers?

In a cave .

Don't knock fractions, not all engineering needs 0.001mm. Try building a bridge without using fractions. Engineering is not just about machined components.

Seriously, the system of measurement should fit the need of the component. An extreme example I saw recently was a motor mount which was dimensioned as 3.4375" overall length. This implies extreme accuracy whereas a fractional dimension of 4 7/16" would have been accurate enough as it is not a critical dimension. Horses for courses.

Regards

T

They only exist in Imperial measurement. 1/2 a metre isn't a technical term.

Whilst knocking the use of fractions, why don't we jibe at number and letter drills ? For us IMPERIAL lot, did any one see drill and reamer sizes in decimal increments - Oh yes please, can I have a 0.35" dia drill. Fractions, letters and numbers are the bread and butter of many of our old drawings as too are milimeters for newer drawings - so don't knock it when us traditional enginers use a bit of modern metrology to connect with the past.

Hmmmm, what a vulgar discussion, let us hope it stays rational and proper, and doesn't veer into the improper.

Regards,

Andrew

I has some old plan of model engines and steam engines, there is still imperial fractions as main measurements. To make precision work by imperial fraction measured by digital caliper is not precise as the caliber without digital. I learned out there is a gap when i moved the movable jaw a little bit at digital caliber while the digits of imperial fraction is still unchanged. Best to use the old caliber and micrometer or for digital freaks: use 1/1000" decimal instead imperial fraction when we are talking about exactly fit between two parts.

John Stevenson, we has gone out of imperial measure in wood work about 1975-1980 in Norway, all wood materials is dimensioned in centimetre and metre. For smaller wood to example hobby use is measured in millimetre.

Following the Norwegian connection - What do metricated carpenters do for measuring 19.2 iches? A bit of metric rounding could put the whole job out and leave you with a leaking roof.

Engineers use millimetres and metres.

Only the BBC and dressmakers use centimetres.

John S.

Bazyle, we are using metricated material in old house who is builded in imperial measure to example exterior wall cladding when we are replacing 2-3 the rotten old planks in 6" with new 16 cm planks at wall cladding and we are using router to adjust right measure in 6" at oversized plank 16 cm before we dress the new adjusted planks on wall. No problem

Unfortunately so do Maths teachers and the French!   Fortuntely the decimetre seems to have disappeared

Regards

T

Edited By Terryd on 26/04/2012 07:26:24

I quite agree John but there are still those who insist on using the so called imperial system. Btw I have been campaigning for the abolition of the centimetre for years.

Regards

T

I don't mind cm or thou' - but what I can never get is the 0.0001mm. Or is that .00001mm ?

Why not use micrometres in a similar way to the electronic fratenity who use microamps, volts or farads ?? No getting the magnifiying glass out to see how many noughts there are or where the decimal point is !.

So 2.5 micrometres is 1 thou. That seems a lot easier to read than 0.025mm !

W.

Errrr, I make 1 thou equal to 25.4µm - Andrew

A thou is one thousandth of an inch or 0.001 (to state the obvious). therefore it is quite logical to talk about a hundredth of a millimetre or 0.01 (approx 4/10ths of a thou'! ) and forget imperial. It is the mixing of terms as you do that causes any confusion.  Not many folks in engineering would work to 0.001mm (approx 4 hundredths of a thou or 0.00004" - now there's a lot of noughts!) let alone 0.0001mm.

And if you find 0.01mm difficult to read how do you manage with proper engineering drawings? Now that thought I find confusing.

T

Edited By Terryd on 26/04/2012 16:21:59

Can anyone explain why americans refer to thou's as mils?

Martin.

Actually, American engineers don't, generally.

I assume mils comes from the prefix "milli-". Another example of mixing systems?

re: mils.

I used to work for BT and it's predecessors as a technician, and we always used to refer to relay distance adjustments as "mils". Interestingly, relay springs were tensioned in "g's" for grams leading to this sentence in my Telephony Vol.1, originally written in 1947 but I assume updated and corrected before I bought my copy in 1959:

"When a relay is fitted with 12 mil springs, tensions (c) & (e) are reduced to 11-15g and 21g minimum respectively, and the relay is given a green label."

To the best of my knowledge, "mils" was the same as "thous".

A possible reason for it may be due to the same logic whereby litres, metres, ohms, volts and a host of other measurements have always used prefixes such as milli- to indicate values which are one thousandth of the base value, hence if the inch is considered to be a base value, then "milli-inch" would be the thousandth part. Custom & practice, and human laziness, would soon ensure that milli-inch quickly became "mil"

Regards,

Peter G. Shaw

Something rarely admitted is the way that fractional meaurements can make design a lot easier.

Imagine you have a stack of different bits, flanges, shoulders etc. that all need to add up to a particular total dimension, but their individual sizes aren't critical.

It's surprising how much easier it is in fractions.

Think of a steam cylinder with a flange each end, 1" long. 1/8" flanges and 3/4" for the body -will that do?

Neil

ARC for one is doing these at £8.00 a pair and to be honest at this price they are consumables.

dunno if im going blind or stupid - poss both, can anyone give me a link to the arc website, im finding nothing to do with tools on google ??

Mike,

http://www.arceurotrade.co.uk

This one?

Pekka