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Measurement confusion


#1

I have to admit that although I learnt the Imperial System of
measurements at Primary School I entered the trade after this
country went metric, but I cannot for the life of me understand why
the jewellery trade in countries where the authorities have not
taken the giant leap into “the world of tens” have not taken it upon
themselves to do so. It has to be so much easier.

We deal every day in small weights and measures - going metric
eliminates confusion of “How many x’s are there in a y?” - it is
always going to be 10 (or 100 if dealing in the larger measures).

It is not as if you haven’t gone part way already! How do you
explain the origin of the diamond carat? Five carats to the gram.
Easy. It isn’t 151.xx carats to the avoirdupois ounce!! (Yeah… I
know someone is going to pipe up and point out that the system is
blown already with this being 5 and that the actual orign has to do
with the weight of carob beans).

Confusion reigns with so many alternatives B&S gauge vs. thousandths
of an inch, troy ounces vs avoirdpois.

If nothing else this should get some discussion going with many
probably wanting to stick with the old ways.

See ya! Roger


#2
but I cannot for the life of me understand why the jewellery trade
in countries where the authorities have not taken the giant leap
into "the world of tens" have not taken it upon themselves to do
so. It has to be so much easier. 

I’m with you here Roger. It always bugs me a bit when our American
compatriots talk in “gauges” of silver. If I really want to know what
actual measurements they are talking about I have to drag out “Oppi”
(which is too darn heavy) to check the conversion charts which never
match perfectly to our beautiful and practical millimeter
measurements anyway.

Ah well…
Cheers, Renate


#3
Confusion reigns with so many alternatives B&S gauge vs.
thousandths of an inch, troy ounces vs avoirdpois.

Dunno, Roger, as far as I know the jewelry industry has been almost
entirely metric all along. Here in the states we still use inches and
feet for larger distances - chain length… Gauges are traditional
(i.e. everybody understands them), but I don’t use them anyway, I use
millimeters… Certainly weights are metric everywhere, all gemstones
are measured in metric, on and on… Talk about tradition, though -
we use pennyweights instead of grams, because a dwt. is exactly 1/20
of a troy ounce, instead of 31.1 grams…


#4

Hello

Jewelry is almost always in metric terms but many websites will give
you a handy desktop converter to install free if you need one…Hoover
and Strong is one source for instance, Cooksons, and I think Kitco,
and calculator.com all have free converting calculators to use on and
off line…rer

[edit]

Check out Ganoksin’s own collection of unit’s conversion
calculators.

[/edit]


#5

Metric measurement for small items is generally easier but it does
have its drawbacks. For instance, what precision do you work to - do
you work to the nearest 1/10th mm (about 4 thou) or to 1/100mm (an
impracticably small unit for machining purposes)? Threads are also
something of a problem - there is no variety suited to different
purposes just ‘standard pitches for different sizes’. A great deal of
work was done by the likes of Whitworth and his contemporaries in the
19th century on finding the ideal thread pitch and form to achieve
maximum strength and holding power for screw threads in different
materials - the metric system ignores all this and has just the one
’universal’ thread form which, like most ‘universal’ systems, falls
short of every ideal. In the UK it is interesting that since we had
the metric system forced upon us in the 1970’s, it has never been
completely accepted. For instance, DIY stores will sell 2x1 timber in
1.8metre lengths (the old 6 foot) and the size of many items are now
listed as the direct metric conversion of their original imperial
size - a standard brick is 215 102.5 65mm ( I wonder who checks
that.5mm dimension). Most people, even the youngsters, still think of
their weight in terms of stones and pounds instead of kilograms and
hospitals will routinely note down a patients weight in kilos but
tell the patient in stones and pounds… All highway speed limits
are still in miles-per-hour rather than kilometers-per-hour and
distances on signs are still in miles. One of the biggest
difficulties with metric measurement is in visualising the sizes.
With Imperial we carry around with us a set of approximate measures -
and inch being the length of the thumb end ( or, in my case, its
width), 4 inches being the width of the palm ( a ‘hand’ in horse
measure), a foot is obvious, a yard from the nose to the tip of an
outstretched arm or a decent sized pace and 6 feet the total span
over outstretched arms. Finding similar approximations for metric
measures is difficult. The system is further complicated by
inconsistent education - young children are taught about centimetres
as the fundamental unit because that is a size they can see and
handle conveniently but, in the ‘real world’, centimetres are hardly
ever encountered. Finally, everyone has to have a working knowledge
of both metric and Imperial units as so much historical information
is still relevant whether that be in the form of property deeds or
granny’s cookbook.

As a watchmaker I suppose I am more exposed to different measurement
systems than most as I have to use not only metric and Imperial. but
also old French inches (which are different to Imperial inches) in
the form of Douziemes (1/12th French inch) and Dixiemes (1/10th
French inch). 1/8ths of French inches were also used and, just to
complicate matters further some watch glasses were sized in
millimetres and eighths!!

Best wishes
Ian
Ian W. Wright
Sheffield UK


#6

Hi Renate,

If I really want to know what actual measurements they are talking
about I have to drag out "Oppi" (which is too darn heavy) to check
the conversion charts which never match perfectly to our beautiful
and practical millimeter measurements anyway. 

Why not get out 'The Complete Metalsmith" by Tim McCreight? It’s
alot lighter in weight & if you spill something on it or in any
other way damage a page, you haven’t ruined an expensive tome. It’s
got all the conversions in it that I’ve ever needed.

Dave


#7

Hi Renate,

I'm with you here Roger. It always bugs me a bit when our American
compatriots talk in "gauges" of silver. If I really want to know
what actual measurements they are talking about I have to drag out
"Oppi" (which is too darn heavy) to check the conversion charts
which never match perfectly to our beautiful and practical
millimeter measurements anyway. 

Would there be any value to using gauges as a convenient measurement
system if one wants to know how much wire can be made from a
particular volume of metal?

If my calculations are correct, by reducing a piece of 16 ga. wire
to 19 ga. the length will double. A handy thing to know if
manufacturing or for calculating certain design costs, but I do know
what you mean about the nuisance of having to convert. I’m still
waiting for the decimal day to be adopted worldwide. We’d finally get
those extra hours in the day we’ve all been wanting for so long.

All the best,

J Collier
Metalsmith
http://jlcollier.com


#8
Metric measurement for small items is generally easier but it does
have its drawbacks. For instance, what precision do you work to -
do you work to the nearest 1/10th mm 

The level of precision within mm is personal and/or dependant on the
application, and very easily done using mm down to however many
decimal points you need. Or you can use use 0.5mm divisions.

A friend of mine likes to spurn the.5 half-measure preferring the
…2.4.6.8mm divisions within a mm - a fairly simple level of
precision.

What is practical and so useful about metrics is you can safely
multiply and divide the numbers and reach mathematically
understandable results. For eg, making hinge pin wire that’s 90% of a
given hole diameter. Divisions or multiplications of the gauge system
is not very intuitive to me at all… unless they’re committed to
memory.

And can you make half-gauge or third-gauge measurements if you really
needed them? That’s always puzzled me.

A great deal of work was done by the likes of Whitworth and his
contemporaries... 

That’s an interesting point. Might we assume that Whitworth threads
could as easily have been originally metric. So the current metric
thread set could be expanded to those that more closely conform to
Whitworth.

Brian
Auckland NEW ZEALAND


#9

Hi All:

Speaking as a yank who’s been trained in England, (London: The Cass)
the way I normally do things is to pick a system and run with it
until I need to change. Very rarely do I convert between them.
Because in addition to all the fun with various gages, (of which
there are several), number drills have been sadly neglected in this
tale of woe. At least over here in the States, most of our smaller
drills come in ‘number’ sizes. Zero through about 80, getting finer
as they go up. (about.120" to bloody fine. ?.005"?) I think the
numbers relate to Stubbs wire gage, but I could be wrong. They most
definitely don’t have anything to do with B&S, which is what we use
for precious metals. Just in case you think it’s that simple, there’s
also another gage system (ASW) that’s used for ferris metals. No,
of course B&S and ASW don’t match up. They’re offset by about 2
numbers, IIRC. But that’s not as much fun as the day I walked into
Blundels my first week in London to buy some sterling sheet. Planning
on doing some raising, I asked for a 6" square of 16 gage. It
arrived, slightly thicker than I thought it should have been, but not
too far off. Turns out the Brits use Birmingham gage for precious
metals, and that runs backwards of the American gages. (0 is very
thin, and 30 is very thick.) Luckily, the crossing point is right
around 16 gage.

Are we having fun yet??

In practice, what I do, and what I suspect most other folks do is to
work with gage for thickness of sheet, unless I need to do something
quantitative with it, at which point I pull out the digital
calipers, and figure out how thick it really is, in decimal inches.
(.0015" resolution.) Alternately, if it’s a rock or something, I’ll
work in decimal millimeters. All it takes is a push of the button on
the calipers to flip between the two systems. What I don’t do is
worry about doing anything with the other systems except calling for
something by name. If I need to match a wire, I mike it, and then go
fishing for a drillbit to match, as measured by the calipers,
regardless of what the ‘number’ says it should be.

I’ve given up on ounces for weighing things at school. Everything’s
in grams, and we don’t worry about troy, imperial or avoirdupois
ounces, or the variations thereof. Besides, you never have to ask “Is
that a liquid gram or a solid gram??”…

Sigh… Just give me decimal somethings. Fractions are tools of the
devil.

Brian.


#10

The wonderful thing about standards is that there are so many to
choose from.

Regards, Gary Wooding


#11

Hi Brian,

A great deal of work was done by the likes of Whitworth and his
contemporaries…

That's an interesting point. Might we assume that Whitworth threads
could as easily have been originally metric. So the current metric
thread set could be expanded to those that more closely conform to
Whitworth. 

The point here was that a lot of work, over a long period of time,
was carried out to find the best possible pitch and thread form for
each particular material. Whitworth was mainly looking for a thread
which would hold best in cast iron and mild steel and chose a thread
with an included angle of 55 degrees with a fairly coarse pitch and
with rounded roots and crests to the threads to relieve stress. At
about the same time, Sellers in the US developed a ‘standard’ thread
which had a 60 degree included angle but had flat tops and roots to
the threads which made it a bit weaker. This thread was variously
known as the ‘Franklin Standard’, the ‘Sellers Standard’ or the
’United States Standard Thread’. This, despite its drawbacks, became
the model for the current metric threads. Prior to, and while
Whitworth was developing his standard thread, however, it was
recognised that a thread which held well in cast iron wouldn’t
perform as well in a softer metal like brass or silver and that the
thread would either tear or bind onto the screw and so many other
threads were in common use. The ‘British Association’ thread ( BA )
was designed principally for small brass fittings such as electrical
connectors and had an included angle of 47 1/2 degrees and a fine
pitch - there was a close relationship between this thread and some
of the metric threads then in use in Europe for watch and clock
making etc. If you look at my table of screw threads at

http://tinyurl.com/plygdx

you might get some idea of the diversity.

One of the main drawbacks to standardisation on the metric standard
from an engineering point of view is that suppliers very quickly
take advantage of the opportunity to reduce their range of available
nuts and bolts to just the metric range and, in the UK, it is now
almost impossible to obtain new supplies to replace damaged nuts and
bolts on old machinery. ( Before people jump in - I know that they
are available if you search the 'net but obtaining them is not as
quick and convenient as formerly and costs much more ).

Best wishes,

Ian
Ian W Wright
Sheffield UK


#12

One of the first jobs I had when leaving the Marines in 1979 was as
a mechanical drafter for a company that made screw products. What an
eye opener! I knew there were different threads. Metric vs non
metric, coarse vs fine, but I had no idea there were so many more.

I learned that each has its most appropriate application. Since
there are myriad applications, and more coming along as time passes,
there will be modifications to current thread forms, thereby creating
no ones. This doesn’t include the variations you can get by varying
the tolerances, manufacturing for a loose, standard, or force fit,
etc.

In some ways it’s like the thread regarding languages we recently
had; it evolves to meet current needs of the users. The only constant
is change.

Mike DeBurgh, GJG
Henderson, NV