Question for designers...



Yeah, I'm sure the same thing would happen in the US. It would only be the younger generation that would adopt it. But until it's forced, the younger generations keep getting addicted to the Imperial system and become one more generation that will never change. Even though they are all now taught the metric system in school at the same time they learn the Imperial system, because they don't use it in their day to day lives they never really learn to think in metric terms. Gasoline, milk, and water is sold by the gallon, everything is sized in inches, temperature is reported in fahrenheit, distance is in miles and speed limits are in MPH. Until all these day to day things are forced to be converted to metric, the younger generations will keep growing up to be one more generation that will refuse to convert.
Even though the advantage of metric is small, and the conversion cost very large, there's an on going cost associated with supporting the dual system that is time and money wasted every year you put off he conversation. Mechanics have to have two complete sets of tools, children are taught two systems in school, manufactures that try to support multiple markets have to produce produces that are compatible with multiple standards (from rulers to printers, to paper sizes to mechanical standards etc).
I think it's inevitable that the metric system will be the world standard (and it already is in many fields like science and medicine) and all of us still in the dark ages will have to convert at some point, so the longer we put off the conversion, the more time and money we are wasting supporting the dual systems, and the more we continue to isolate ourselves from the rest of the world.
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Curt Welch http://CurtWelch.Com /
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On Aug 27, 12:02 pm, snipped-for-privacy@kcwc.com (Curt Welch) wrote:

Yes I can see that. I guess there are political reasons why reason doesn't prevail on the metric issue in America.
-- jc
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It's because reason for the most part doesn't prevail in America. We allow personal emotions to rule over reason. We use fancy words like freedom to allow us to be stupid. Most people only care about how much of a pain in the ass it would be for them to have to learn a new system and since they don't see any personal gain in it for themselves, they reject the idea of converting. The fact that it would make the nation stronger as a whole in a increasingly international economy is something the average guy on the street refuses to care about. They bitch about jobs being lost to international markets but then refuse to do anything hard to actually become more competitive in those markets.
I don't see this attitude changing anytime soon. Maybe the increased international awareness the Internet is creating for Americans will make them start to think about these issues a bit more?
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Just rambling here... but my Machinery's Handbook has 2512 pages of very small print formulas for everything from the proportional formula, through trig and everything you ever wanted to know about screw threads, tapers, and proven mechanical wizardry in the inch/pound/hp world. Also enough on the SI to keep me awake at night. My Mechanical Engineering manual is just as prolific. I would hate to think of the mess we world be in if forced to convert all of that experience into something that really does not make that much sense...
I'm probably mistaken, but I believe the metric system was determined to be our national standard as far back as when Washington was our president. But it just is not that good to cause a national referendum on an apparently needless change. We are the world leader in technology. Let the rest of the world catch up to us by converting to imperial!
I was brought up with the metric system in my school, drafting, geometry and all that stuff. I started serious design work in the metric system and ended up pulling my hair out at the total confusion of that damned decimal point and where to put it. So I took up feet, inches, pounds and fractions. In my shop I have my little block with a quarter twenty tap and number seven drill along with my other fractional taps and either fractional drills or numbered drills or metric.
I think we should be able to use both systems. The metric system seems to do very well in the lab where really small stuff is measured and mixed. One cc is one gram and a thousand grams is a kilo. I can buy that. But in the shop... all of my machine tools are dialed in inches, my gears ratioed to cut threads per inch, and for me to scrap all of that just to buy something that does the same only in metric is really pushing it. So I have a set of wrenches in metric and another in inches. That's ok.
Wayne
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This seems very odd to me. You find it easier to multiply and divide by numbers like 12, 16, and 144 than numbers like 10, 100, and 1000?

Indeed, I'd say we have to, in the U.S. at least. I tried to keep my tooling metric, and that lasted about a day, before I ran into something where I had to use imperial units, either to work with some part I had, or because the local hardware store only had an imperial part near the size I needed.
I don't have to like it, but until somebody passes a law banning all that imperial stuff, I have to live with it.
Best, - Joe
--
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Joe Strout wrote:

A half inch is 1/2"; a quarter inch is 1/4"; a sixteenth of an inch is 1/16"; three times that is 3/16"... A half centimeter is 5mm; a quarter centimeter is 2.5mm; a sixteenth of a centimeter is 0.625mm. What's three times that? Plus your metric set probably only contains multiples of powers of 10... so most of these sizes aren't available...
Unit conversion usually only happens in higher-level design tasks such as "how long are 50 Xs" -- at which point the unit conversion only incidentally hinders an otherwise complex operation. Hence "scientists prefer" metric while "laymen prefer" English units. Besides, is 32.17 slugs/pound really harder to remember than 6.022*10^23 atoms per mole?
Decimal is a horrible base for practical use. The ancient Babylonians had it right - base 60 contains all the small primes, making all common fractions readily available.
But pi is the optimal base from a theoretical perspective -- it optimizes the tradeoff between how many symbols exist and how many symbols are needed to express a given value -- but nobody uses it since its difficult to represent integers... And binary is natural on computers...
- Daniel
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wrote:

geometry and

ended
point
Awesome response Doctor Daniel! I must put this in my reference material for sure. Makes sense to me!
Wayne
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Or 1/2 cm.

OR 1/4 cm.

or 1/16 cm.

3/16 cm.

If the sizes you need aren't available, you bought the wrong tools. I don't really get your point.

I don't buy it.
The only laymen that prefer Imperial units are the ones that never learned to work in metric units.
The fraction system used with inches is a base two system so you can only divide easily by powers of two. Decimal metric units at least makes it easy to divide by 5's as well. What's 1/5 of a cm? 2 mm. But what is 1/5 of an inch? Can't really do it easily.
The bottom line is that both systems have special cases that are easier than the other systems, but that in real life, not much happens in those special cases. You have something 6 3/16" or 15.7 cm and you want to divide it in 4ths and it's not trivial in either system. But at lest, with the metric system, you can pick up in $5 calculator and do the math directly since all our calculators work in decimals. But in imperial units, you have to play all games to figure it out like converting to decimal, then doing the math, and then trying to convert back to fractions, or dividing the inches and the fractions separately and adding the results.

The only thing worse is the mixed-base system of Imperial units. Base 12 for inches, base 2 for fractions of an inch, base 10 for feet.
Metric units are better because there is no conversions required since we do all our math in the decimal system already. Or the only conversion is learning where to put the decimal point instead of remembering what to divide by (12, or 4, or 8, etc).
If all you have to do is measure something, any system would work fine. You could put random marks on a tape and label them TOM, DICK, and JANE, then make it the standard and it would work fine. You just tell people the desk is 3 marks past JANE wide. But when you have to do math, like adding two numbers, or subtracting, or dividing a length into equal parts, then metric is a clear win because it's directly compatible with the decimal system we use for doing math with.
In most shop work, we learn how to do the math problems without doing math. Instead of measuring the width and subtracting another width, we just use the work piece like a slide rule and measure the first dimension in one direction, and the second dimension in the other direction so we don't have to do the math. As long as all work can be done that way, then we could just as easily use the TOM, DICK, and JANE ruler. But the minute you have to do math, Imperial sucks, and metric wins big time.

Base 60 would suck big time. You would have 60 symbols to memorize and the multiplication table and addition table you would have to memorize would have 3600 locations in it. The kids might get it all memorized and learn how to add by 6th grade if you were lucky.
Base 12 would probably be better than base 10, but again, the cost of converting the world to a base 12 system would be a real bitch.

I wasn't as impressed with the logic.

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Like 3/16, for instance?

I think you mean e (base of the naperian logarithms). When I lived in Seattle around 1980, there was a group in town advocating the use of base e for all numeric representations. I was never able to tell from their literature whether they were the most batsh*t crazy loons in town (which in Seattle would be saying a lot), or one of the most long-lived, best-done parodies I've ever come across.
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wrote:

and
ended
point
work.
<http://www.strout.net/info/science/polywell/>
The public opinion that the metric system is easier to use because you just move a decimal here and there is totally unrepresentative of the nature of the beast.
The metric system has, from day one, forced one form of traditional measurement into a kind of decimal equivalent that requires a long stream of unwhole numbers (unholly?) for it to even resemble the original.
I find it necessary to imagine the end result of my calculations as viewed in the real world. Thus, when my end result for a shaft on the drive from a stepper to the wheel and my calculation shows ten inches, I can visualize ten inches. I can't visualize the hundreds of millimeters required to do the same in the metric system. I really can't visualize five ft. two and eyes of blue in centimeters, nor one hundred and ten pounds in kilograms.
So yes, to me it's much easier to tap for a quarter twenty screw into a piece of metal after drilling a number seven hole.
If there had been a solid reason to go metric, this country would have been the first to do so.
As we were in getting into the computer mania.
Wayne
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Whether you work in 746 Watts or 1 Horsepower, the behaviour of your robot is not in the least affected.
The importance is the design and not the units of measurement which can be freely converted to and fro, 2.54mm being exactly an inch.
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wrote:

I have used both. I prefer metric, but usually use inches because here in the USA metric components are much more expensive. It is silly to design in metric if all your screws, shafts, bearings, etc. are in inches. The dials on my lathe and mill are also in inches.

I think a major factor was Napoleon's decision to invade Russia in 1812. That led to a diminishment of French influence.
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I've got a feeling that the inch is _defined_ as 25.4 mm. The previous definition was something vague like the length of three barleycorns, or something.
In what way are amp(ere)s not metric?
Deep.
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    --FWIW I prefer inch, because most of the parts I'll want to tack onto any beastie I build will be listed in catalogs with FPS, rather than CGS dimensions. If you're not in an "imperial" country you'll probably want to stick with metric.
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Inches.
It's what I'm used to, and what my rulers are marked in (I've got pretty extensive tool sets in both metric and SAE since I do a lot of car repair as a hobby. But you don't do much measuring when working on cars, so my rulers are all SAE).

While any sane person will recognize that the metric system works better, it's not anywhere as crushingly superior as they told us when I was in school. It's real advantage in europe wasn't that it was better than the old system there, it's that there wasn't a continent-wide system in place: every town would have its own notion of the length of an inch, and there might well be units that were only in use in particular localities. As transportation got better, there was a need for a system of units that was consistent over a wide area. That was the real advantage there.
In the US, there was a nearly continent-wide system in place from the beginning, and there hasn't been a compelling reason to change. As we have more and more international trade, the pressure to change gets stronger and stronger for exactly the same reason as in europe, only on a larger scale.
Of course, tremendous amounts of industry have changed, for exactly that reason. I don't thing there's an SAE fastener on any of the three American cars I've bought that were built in 1995 and later. By contrast, I don't think there's a single metric fastener on my 1978 Newport.
Just by the way, you do realize that amps are a metric unit, don't you?
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writes:

centimeters,
the
---- Right. As I recall it was one of the first conversions from the standard HP, Watt and Volt.
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Wayne Lundberg wrote:

The U.S. already has a well established, and powerful metric system.
It's called the Dollar!
Don...
--
Don McKenzie

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It's getting there indeed. The stock exchanges have switched from fractional share value (as in 2 7/128) to decimal dollar amounts a few years back.
Metric is not necessary in everyday's life, and the US is hugely invested in the imperial system. However, in time, I trust metric will be adopted, just like stock exchanges have broken with a century long tradition of using fractions.
Serge

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I do it in metric.

Because it's easier, and I'd rather focus on designing my robot than on multiplying and dividing by weird numbers like 12 (inches/foot) and 16 (oz/lb) and so on.

Because competent engineers can learn to deal with any units, especially with the help of computers, and it really doesn't matter that much (apart from the occasional lost billion-dollar space probe).
--
"Polywell" fusion -- an approach to nuclear fusion that might actually work.
Learn more and discuss via: <http://www.strout.net/info/science/polywell/>
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Wayne,
France IS the leader in technology (if you ask the French, that is). ;^)
Jeff.
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