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  • J Tiers
    replied
    Originally posted by ulav8r View Post
    The main reason to know that you will receive material at the low end of the tolerance range is for design and for strength calculations. If you "need" material at the mid to upper range of the tolerance, you will have to acquire thicker material and cut it down to the thickness you "need". So far as strength goes, everything should be designed with a safety factor well above the next size up. IOW, if 12 gage is just barely strong enough at the upper end of the tolerance, you should be using at least 10 gage material.
    That's the point, isn;t it?

    Calculate strengths at the low end of thickness, and calculate worst case fit-ups at both low and high ends of thickness.

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  • ulav8r
    replied
    The main reason to know that you will receive material at the low end of the tolerance range is for design and for strength calculations. If you "need" material at the mid to upper range of the tolerance, you will have to acquire thicker material and cut it down to the thickness you "need". So far as strength goes, everything should be designed with a safety factor well above the next size up. IOW, if 12 gage is just barely strong enough at the upper end of the tolerance, you should be using at least 10 gage material.

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  • Ian B
    replied
    I knew an old woodworker who lost 3 fingers on a planer / thicknesser. I asked him what the hardest thing was about having lost them.

    He said "counting in base 7..."

    Ian

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  • Paul Alciatore
    replied
    Why do we have gauges for sheet metal. I believe the reason goes something like this. Sheet metal was made before we had good measuring instruments like Vernier calipers and micrometers. It was not easy to measure the actual thickness of the sheet metal. But they had to have some way of measuring it. Scales for weighing things have been with us since antiquity, probably to measure the amounts of gold and silver and other valuable things. So a piece of sheet metal could be weighed with some accuracy. Once a sample of the correct weight was made, then a simple gauge could be made to just fit that sample and we had a standard gauge that could be used on the manufacturing plant as well as the point of sale and in the shops that used it. No mike or caliper was needed, just the GAUGE.

    But why are the sizes in such an odd succession? Well, those manufacturers probably determined that certain thicknesses, certain weights per square foot, were good for various things. They developed a succession of these weights that produced a range of thicknesses that were useful for different purposes. So they standardized on that set of numbers. It should not be any surprise that those numbers do not form any simple or linear relationship with each other. Many things in our world need to increase by unequal amounts to produce similar changes. Sounds are measured in Bells and deciBells which comprise a logarithmic scale, not a linear one. This is because the intensity of the sound and it's apparent loudness to our ears are not directly proportional. Likewise for many other things, including the usefulness of sheet metal of different thicknesses.

    So the gauge system was based weight, which, in days of old, could be easily measured (1 NECESSITY). And the odd distribution of sizes was probably due to the variety of uses for sheet metal (2 PRACTICALITY). Once the system was established, it became hard to change it (3 MOMENTUM/TRADITION). "But I always use 18 gauge. If you don't have 18 gauge I will find someone who does and buy it there." It does not take much of that to convince a manufacturer that he really should make sheet metal by gauges.

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  • Paul Alciatore
    replied
    I believe that number was based on getting maximum fuel economy in the most cars. This was back a few decades ago and we still had gas hogs.

    But this is getting into politics and we are not allowed to discuss that here so I will stop now.



    Originally posted by Doc Nickel View Post
    Well, we once 'standardized'- sort of- on a 55MPH speed limit. Why such an arbitrary number? It doesn't relate to anything, since the distance you travel on average is rarely exactly 55 miles or lasts exactly an hour. It's no even multiple of car lengths, or distances between destinations.

    So clearly we should "metricify" it, call it "Speed Ten". In residential areas, it might be Speed Five. Out on the highway, raise it to Speed Fifteen.

    See how much more clear and obvious that would be? You could use it to rate everything from racehorses ("Speed 200") to bullet trains ("Speed 2200".)

    Clearly it's obviously a better solution- "better" in this case meaning we actually based the new unit on a common constant- the average speed limit. SO much better than using random, arbitrary numbers...



    Doc.

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  • Paul Alciatore
    replied
    Rats, you beat me to it.



    Originally posted by Toolguy View Post
    Yes - it's the thickest steel a 12 ga. shotgun can punch through.

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  • J Tiers
    replied
    Originally posted by greystone View Post
    "Gage" for any measurement is a horrible system.
    It indicates a size, in a particular place for a particular item, with no known reference to location, historical date, material, use, etc.

    And it does *not* scale up conveniently for mass, length, volume, area, etc....
    You are of course correct. But you are seeing the wrong end of it.

    Think of yourself being in the 1600s, not having any clue about micrometers, etc, where the length measurements are suitable for measuring cloth, etc.

    You find that a particular thickness of "something" was just perfect, and since you make this fairly often, you want to be able to repeat that thickness. So, you whittle, file, or otherwise make a gage that fits that thickness. Now you can repeat that thickness at some later time, since you just need the gage to fit over it snugly to know it is right.

    Later, you need another, and pretty soon you have a bunch of them, which you proceed to number in general order of size.

    You do not NEED any of the reference to location, date, etc. All you want is to be able to make the thing again with the same material thickness.

    That is how gages start. Sometime in the far future, someone may still be using old Johannes' gage system, but they don't know where it came from. And they dont have the actual measuring gage Johannes made, but they know what size fits gage #18.... that is "18 gauge" material.

    Now in today's world, there may be cases where you need to know the thickness, but usually you can just call for 18 ga. When you do, you get material that would fit old Johannes' gage number 18.

    What your commprehension issue is, relates to demanding numbers as the "name" of the thing. It is exactly the same thing if you call it by a different "name", like 16 ga, 18 ga, or the like. And you do not NEED the numbers to use it even.

    Things are labeled as good for #10 to #16 wire, and that is what you need to know. If you are an electrician, that instantly tells you if that device is suitable for a 40A circuit (no, it is not, at least not all in one wire).

    Does an EU electrician know the same things from the "number" type name? Of course. Potato, potahto, pomme de terre.

    The number and letter etc drills is a different story. Those are hard to justify, but are traditional, entrenched in tables and handbooks, and somewhat effective. And they link up with threading, clearance holes, etc for "imperial" threads. If they were really unworkable, they would have been done away with long ago.

    Personally, I think they are silly, but I can work with them.

    But, I do not quite understand the demand by so many that others should use the particular system that they (the many) happen to think is best. People are practical, and will use what they need to. No reason to force the use of what you personally think is "obviously better".

    I also think some EU stuff is awfully silly, particularly electrical.

    Switches etc are rated to be "just barely good enough" to fit one of the 40 or so "categories of usage". And, to last just long enough. A slight overload, and the unit must be replaced. As if a tiny bit more material would break the bank.... Instead of that, US folks make switches to cover a known defined range, and let it go. If a switch or contactor is a bit "too good" for a usage, that is OK to avoid having so many categories and decisions on what is just good enough to cover the situation.
    Last edited by J Tiers; 10-28-2017, 05:37 PM.

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  • greystone
    replied
    "Gage" for any measurement is a horrible system.
    It indicates a size, in a particular place for a particular item, with no known reference to location, historical date, material, use, etc.

    And it does *not* scale up conveniently for mass, length, volume, area, etc.

    A railroad of gage "x" is not defined - afaik - as different countries used different gages, and at different times.

    Similar applies to "barrels" since they might be for anything from wheat to oil to...
    Or ounces used in many things, liquids, labs, metals, others..28 / 31 g, 28 / 29 ml, etc ..

    Wire of 1.5 mm sq2, 4, 6 are exact definitions of various household wiring per power required per voltage.

    Letter or number drills .. I have zero idea what they are.

    Every specified hole in inches n.nnn is an exact size and I can convert it to mm if I need to.
    Mostly I don´t need to, but can, very easily.
    With +/- tolerances or a size range if appropriate.

    I don´t *mind* working with inches, feet, miles, mph etc.
    And for old-school engineering in metal, "thou" and 0.001" units were/are actually extremely convenient.
    0.001" is just right for fits, sizes, feel, good/bad, old gages in go/no-go etc.

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  • Illinoyance
    replied
    ed_h
    Not sure about rolling steel sheet. In an aluminum rolling mill the largest mill stand had hydraulic cylinders to actually bow the rolls to compensate for deflection. I understand now the rolls are contoured in a subtle curve kind of resembling coke bottles. Upper and lower rolls have their curvatures facing the opposite way. The rolls are shifted endwise to tighten or loosen the distance between the rolls in the middle.

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  • Ridgerunner
    replied
    I'll take a baker's dozen of doughnuts and put them in a poke please.

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  • ed_h
    replied
    Originally posted by ulav8r View Post
    Another thing to know about buying by gage #, there is a tolerance limit and the material you get will most likely be a the very bottom of the limit.
    According to Wikipedia, the tolerance is necessary because the rollers used to size sheet metal will bow slightly in the middle, causing the edges of the sheets to be a little thinner.



    Originally posted by MattiJ View Post
    Cool. Would be interesting brain-twister if we had another half of population using base-12 for everything.
    It has quite potential but the base-12 measurement units in base-10 math is just crazy
    There are a good number of people around the world, including me and some others here, I'm sure, who are very comfortable working in base 16.

    Ed

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  • Illinoyance
    replied
    The definition of the mile as 5280 feet, I believe, was established by Queen Elizabeth I to make the mile an even number of furlongs. Prior to that it was a mille passus, a thousand paces which is how the Romans defined their mile.

    Then there is the Gunter's chain of 66 ft., consisting of 100 links. There were 80 chains to the mile. 10 square chains comprised one acre.

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  • MattiJ
    replied
    Originally posted by danlb View Post
    Yep. Let's see... the diameter of a wire with a cross section of .05 sq mm. That would be the (square root of (.05 / Pi ) ) * 2. yeah. I'm going to do that without a calculator or google. Right.
    No, the math savant part was if you actually remember the formulas or conversion factors for the 40 different gages

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  • JRouche
    replied
    Originally posted by J Tiers View Post
    That's actually no problem.

    If the gauge is OK for your application, ,
    Ha,, Yeah, I have to agree with this one. I am a Tech. It seems like most of you are Engineers. I know, too many socks. JR

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  • danlb
    replied
    Originally posted by MattiJ View Post
    Difference is that from 0.5 mm2 you can quite easily calculate the wire diameter without being math savant or having 500 pages of conversion tables.
    Yep. Let's see... the diameter of a wire with a cross section of .05 sq mm. That would be the (square root of (.05 / Pi ) ) * 2. yeah. I'm going to do that without a calculator or google. Right.

    Leave a comment:

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