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  1. #11
    KustomsbyKent's Avatar
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    For much of the design work that I do, I prefer to work in the metric system. Once you're in CAD, it is just a number, the system you're using, imperial or Metric doesn't mean much.
    For engineering calculations involving force, distance, torque, thermal units, etc, it is far easier to use the Metric system. I can remember in engineering school having complex problems in the imperial system. We would convert the inputs to the metric system (easy conversion), do the problem in metric, and then convert the answer back to imperial.
    About the only "advantage" for the imperial system is when working with 2x lumber in the house building sector.... outside of that, I prefer the metric system.

  2. #12

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    Most US manufacturing companies switched to the metric system years ago, most noticeably the auto industry. It's only the die hard knuckle heads who insist on using the antiquated Imperial/American system. One reality is our stubbornness to resist the change to metric costs US industry untold millions of dollars each & every year. Do you really think a European or Asian company will purchase equipment that will require special odd ball (fractional) tools? Come on, simple deductive reasoning answers that question.

    BTW, if you make any electrical/electronic calculations you are using the metric system.

    If you serve or have served in the US Military during or after Vietnam you most likely used the metric system. The "NATO" 155 round that replaced the 5" Naval & other guns is: wait for it is 155mm in diameter. If you have used or heard the term kilcks, that's a kilometer.

    So Marv, I'm a supporter of doing away with this ridiculous inch, feet, gallons, etc system. Quick tell me a gallon of water weighs _______. No cheating by Googling the answer. On the other hand a liter of water has a mass of one kilogram. Which would be easier? Calculating the pressure of a column of water in the American/Imperial system or the metric system? Do you need to ask? If you have a given volume of a liquid, just look up the density and very quickly you can calculate the mass of the liquid.

    On a trip to a German University a professor born in England told me the weather men were immense help in teaching the populous the metric system. Initially the weather was given using both systems and gradually phased out the Imperial system. It could also happen here.
    Last edited by Dr Stan; 06-03-2017 at 03:36 PM.

  3. #13
    [email protected] tonyfoale's Avatar
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    Quote Originally Posted by mklotz View Post
    The main advantage of the metric system is NOT just that its units are based on powers of ten. Briefly, the key advantages are:

    Only one unit used to measure each fundamental or derived physical quantity.

    Just because something uses a powers of ten sequence does not automatically make it metric. Your inch micrometer has markings for tenths and thousandths of inches but it isn't metric. Most money is subdivided into a hundred "pence" of some sort but it isn't metric.

    The fact that something is expressed in metric units does not make it part of the METRIC MEASUREMENT SYSTEM. .
    Marv,
    Yes, yes and yes. I could have written that, I agree completely.
    I would like to add that there are only 3 fundamental units in either of the two systems. viz; length, mass and time. All other units are derived from those. In the metric system there have been several sets of metric "base units" used, often depending on the physical scale of the problem under consideration. e.g. the main system now is MKS or metres, kilograms and seconds, a system, now largely out of fashion, is the CGS or cms, grams and seconds. One big problem with the imperial system is not so much the system itself but the general widespread MISUSE of the system which has lead to many engineering failures of one sort or another.
    The principal base units in the imperial system are the foot, lb and seconds. the misuse stems from the almost universal use of the lb. to also describe force, putting an "f" after as in lbf. does little but pay lip service to the confusion caused by this practice. As Marv pointed out, force is a derived unit which stems from one of Newton's laws and usually expressed as F=MA, in other words force is not the same as mass, it is a function of mass and any acceleration that it is subject to. In the foot, lb and second system the correct unit of force is the poundal not lbf. There are 32.2 poundals to 1 lbf. In the MKS metric system the correct unit of force is the newton or N. not kgf. There are 9.807 N in a kgf.
    Not the fault of either imperial or metric systems but in engineering and scientific circles the metric system is not generally misused. That is Kg is used for mass and N for force, or decade multiples of those. however, even in those technical circles it is common for practicioners to use lbf and lb. in the same calculations.
    So what's the problem? Let's revisit F=MA and imagine accelerating a 1 lb. mass at 32.2 ft/sec^2, then MA = 1 x 32.2 = 32.2 poundals not lbf. so how do we turn that into lbf.? We have to divide by g. (approx. 32.2 ft/sec^2) so MA now = 1 x 32.2/g = 1 lbf. That seems pretty simple, but when calculations get more complex the people developing the calculations often struggle with the notion of "do we divide by g or multiply by it", because that will vary with each calculation. This has lead to several engineering catastrophies. I have never known anyone use the poundal in practice due to laziness, ignorance or misinformation. The aircraft industry which deals with high forces got around this problem by introducing a new unit for mass - the slug. The slug is 32.2 times a 1 lb. mass, so now the correct unit of force becomes the lbf.
    This confusion and misuse of units is not the fault of the imperial system but the way in which it is most often used. When compatible units are used in either system there just simply is NEVER any need to remember to include g in any force/mass calculations.
    This just one example of the problems that is connected to the imperial system, the need for conversion units is almost built in because units which are in common use do not fit with the foot, lb, second standard. take pressure as another example. p.s.i is the common unit but the compatible unit should be poundal/sq. ft. so we need a conversion factor if we are using pressure in other calculations with other units. This conversion factor would be g/12^2. What an absolute mess? In the metric system the principal unit of pressure is the pascal which simply equals 1N/m^2 no weird conversion factors needed as the units are compatible with the base units of m, kg and seconds..
    Little wonder that I embrace the metric system with simple compatible units. The difference is much more profound than what type of vernier caliper you use.

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  5. #14
    mklotz mklotz's Avatar
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    Quote Originally Posted by Dr Stan View Post
    So Marv, I'm a supporter of doing away with this ridiculous inch, feet, gallons, etc system. Quick tell me a gallon of water weighs _______. No cheating by Googling the answer. On the other hand a liter of water has a mass of one kilogram. Which would be easier? Calculating the pressure of a column of water in the American/Imperial system or the metric system? Do you need to ask? If you have a given volume of a liquid, just look up the density and very quickly you can calculate the mass of the liquid.
    Along those lines, to highlight the ugliness of inferial I often pose this problem to its advocates - especially those who think the only difference between systems is the difference between inches and millimeters.

    Without using references or a calculator, compute the number of gallons in an acre-foot of water.

    Note that this problem only involves common inferial units - gallons, feet and acres are encountered frequently. There's no need to introduce the weird units, e.g. furlongs and jeroboams, to create a difficult problem.

    The equivalent metric problem - number of liters in a hectare-meter of water - can be done in one's head.

    Another problem along the same lines goes like this...

    In the world of firearms, muzzle energy is calculated in ft-lb from muzzle velocity in ft/sec and bullet weight in grains. This leads to an equation that is usually written like this...

    Energy (ft-lb) = (muzzle velocity (ft/sec))^2 * bullet weight (grains) / K

    where 'K' is a constant. Calculate the value of K without using any references (a calculator may be used).

    In keeping with Tony's post, your first task is to puzzle out what is meant by the 'lb' shown in the equation.
    ---
    Regards, Marv


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  6. #15

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    It's probably three decades ago when I wrote a letter to the editor of Popular Mechanics responding to a slur regarding the metric system. The heat I took was absolutely ridiculous. My patriotism was questioned along with my education (had a Masters at the time and taught machining at a vo-tech). Even the editor took issue simply saying "I don't like the metric system" or words to that effect. I had a lot of trouble understanding just how "educated" people could be so ignorant, and still do.

    Here we are 30 or so years later and the same issue is still around. All I can say is What The ____? Just how hard is it to stomp out ignorance?

  7. #16

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    Hi and WOW! ... I have spent most of my life working in the scientific area .... metric was kinda adapted by Henry Ford way back .... the bolts had "us" threads , but the head of the bolt was / is metric ...AND as far as I know, the congress of the US adopted the metric system as our "official"standard over a hundred years ago ... but the schools never taught the metric measurement system til lately.so we are at a great disadvantage in the world in some things , but many companies are using the metric system.

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    Just to add a bit of confusion; I (try to) build plastic models; on the subject of car models, you have plenty of scales, but I noticed that a lot of them are in 1/24 (everybody knows Airifx from Great Britain, whose main production was 1/72 : 1 inch on the model is 1 foot on the real plane, so you can imagine that 1/24 scale come from this way of measuring with feet and inches) but most of the car models made in USA are in ... 1/25 scale

  9. #18

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    I still like 12in=1foot, cause i can look down and see something to relate to in size. what the heck does 304.8mm relate to in the real world. 1/3 of of 1 millionth of the equator to North pole.
    Yes I use metric,don't have to like it, didn't grow up with it, it wasn't even mentioned in high school.
    Are we sure it isn't a French conspiracy?
    Marv your dissertation would be relevant had the terminology been correct. "inferial" really?Rather snobbish.

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  11. #19
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    The main use of my machine shop is repair. If I'm fixing something that was designed and manufactured metric, that's the measurement system, vise versa SAE for items designed in that system.

    My engineer training in the late 70s, the physics department was all S.I., but mechanical department classes were a mix of SI and SAE in the text book (e.g. thermo dynamics). The civil engr'ng department was SAE only. Strength of materials was the main class (from my memory), where beams were all SAE (probably because of antiquated text book). But if you have to design a beam today, in the USA, structural steel is rated in KSI (max stress), and building officials only deal in live and dead loads in lbs/sqft.

    I worked on avionics, as an EE (but also did mechanical packaging of PWBs in the boxes). The physical dimensions of everything was SAE. With world wide customers, we always put the SI in parenthesis on all drawings and docs (they were all conversions from SAE, except electrical parameters). ARINC (Avionics Radio Incorporated) captured standard equipment dimensions, and mounting trays. Also connector pinout definitions for interoperability for use of avionics boxes from different vendors. I don't see this changing from SAE....EVER. Even AIRBUS uses ARINC specs, I bet it frustrates the heck out of their engineers. For electrical connectors 0.1inch centers works out well for robust line mechanic mating (e.g. ARINC 600). The DIN 1mm connectors were OK for internal interconnect, but not robust enough for an aircraft level connector. I really don't like seeing connector dimensions of 2.54mm centers. But that's what they are.

    To me, the management was old school (50s through 60s when I started work), and they held on to SAE measurements, so the designs were "phase locked" in SAE. And even with new blood, the 'inertia' to change just never happens.
    The one funny I still recall was the ME group head, had a sign up in his office "Old age and treachery beat youth and skill every time".

    Steve

  12. #20
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    I'll weigh in with this, ALL ancient weights and measures were derived from observations of natural objects and occurrences. They are easy to ratio and work with in fractions. I have a friend who has studied this and ancient archeology for over a 1/4 of a century and his conclusion is that a small error was deliberately introduced into the original measure of a meter. Off topic but if anyone has an interest in how 'codes' were built into various structures around the globe [I]before[I] recorded history as we know it began here's a link. Ancient Celtic New Zealand
    He has some interesting observations about the Cahokia Mounds in Illinois and has just posted about the Druidic Dodecahedrons.

    Back to topic, NZ went metricery in 1969 which was a pain as I had to do my trade in both metricery and Imperial. I happily use both for small distance but use miles for travel. A kilogram is a little over 2.2lb A BTU means something to me but a joule? I keep looking for a jewlers. Metricery also has multiple measures for torque while good old Imperial has lbs/ft a the most basic.
    Now man could not build any of the great pyramids today and guess what? They are built using a measurement system directly compatible with today's Imperial standards, metricery don't work. One point that irks me is that the American system of Imperial measurement is the true Imperial measurement system, the British had theirs corrupted by the Catholic Church and those blasted French.
    There is also the fact that so much of what engineers have built in the world today is based on Imperial measure. I also find working in fractions with Imperial measure is a doodle unlike metricery.
    So I am forced to use metricery and like it for some things but freely swap to Imperial whenever I need to or feel it is the better system for what I am doing.
    Lets keep both OR slightly modify the metrick system to make it better relate directly to the ancient and beautiful Imperial system.

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