82 deg vs 90 deg chamfer
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    Default 82 deg vs 90 deg chamfer

    The new machines we installed this year have metric fasteners. So I ordered a 90 Chamfering bit set for the metric flat heads.
    Got me wondering what the advantage either angle has or just 100 year old tradition.

    Dave

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    Don't know, but metric bolts also have a proportionally larger head too..

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    Who the hell came up with 82? Why not 81 or 87?

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    Quote Originally Posted by Gobo View Post
    Who the hell came up with 82? Why not 81 or 87?
    My guess would be like all great advances it was a mistake that worked. The first company to really make and sell them messed up their first batch and just ran with it. They were successful so everyone copied them.

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    The reason for this is quite neat, screws are 82 degrees, because they were
    meant to replace the nail. The old square nails once used as well were
    not 90 degrees but were indeed on average 82 degrees, and the manufacturer
    of screws wanted to fill the same hole and as such maintained the angle.
    Now why were nails 82 well that comes from how they were made, they were
    cut pieces of metal cut with a chisel and placed in an anvil (for making
    nails) and the top was hammered to give us the flat nail, and mushroom
    head. The Anvil had an 82 degree inpression for this, although not all
    nails followed this convention, just the majority. Now why did the
    anvil have that angle, this goes back to the ancient greeks, who when
    making chariots and eventially banding the wheels, were avid smokers, at
    that time, there were no ashtrays, so the original blacksmiths in those
    days drilled their anvil and placed an angle on to it to hold there
    cigarette. In shops where many blacksmitchs worked many holes had to be
    drilled with and angle to keep the cigarette tilted, so they made a neat
    little drill bit which we call a counter sink. Eventually they the tool
    wore with time and the hole got smaller. In time the hole no longer held
    a cigarette, and was then used to drill anvils for making nails. So there
    you have it, the screw angle is based on the angle required to hold a
    cigarette. By the way I have some swamp land to sell, very high quality.
    Google Groups

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    Quote Originally Posted by winger View Post
    The new machines we installed this year have metric fasteners. So I ordered a 90 Chamfering bit set for the metric flat heads.
    Got me wondering what the advantage either angle has or just 100 year old tradition.

    Dave
    Just know that Metric uses both 90 and 82, but it depends on the size of the screw.
    If I remember correctly, larger than 20MM use an 82 deg.

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    Quote Originally Posted by winger View Post
    The new machines we installed this year have metric fasteners. So I ordered a 90 Chamfering bit set for the metric flat heads.
    Got me wondering what the advantage either angle has or just 100 year old tradition.

    Dave
    Very interesting question! And it begs the question, "Why does metric use 360 degrees?" Why not 100 or 1000?

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    Quote Originally Posted by Yan Wo View Post
    Very interesting question! And it begs the question, "Why does metric use 360 degrees?" Why not 100 or 1000?
    They tried, but it didn't catch on.

    Gradian - Wikipedia

    In the 18th century, the metre was defined as the forty-millionth part of a meridian. Thus, one grad of arc along the Earth's surface corresponded to 100 kilometres of distance at the equator

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    I do not know the true answer, but I have a observation. Multiply the diameter of a 82 deg flathead screw by .6 and you get a countersink depth that places the screw head just below flush.

    The same logic applies to the 118 deg drill point. Multiplying a drill diameter by .3 give the theoretical length of the drill point.

    I am guessing that someone used these angles to make machining calculations easier.

    I just realized that .5 times a 90 deg flathead does the same thing.
    My theory is probably wrong.
    Last edited by jcoehlo; 11-01-2019 at 03:10 PM. Reason: better idea

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    so if the metric system is so great, why don't we have metric time?

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    Quote Originally Posted by Larry Dickman View Post
    so if the metric system is so great, why don't we have metric time?
    That was tried too.

    Decimal time - Wikipedia

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    I am not an expert at this, but I will take a SEWAG at it (Somewhat Educated Wild Ass Guess).

    First, 360 degrees is not a metric thing. Both English and metric measure use it. And there are other units for measuring angles: 400 Grads, 2 pi radians, mils (the angle that subtends 1 m at 1 Km), NATO mill, milliradians, etc.

    Early philosophers (that's scientists in today's lingo) sometimes had a need to measure short internals of time. But the hour glass was ill suited to this task. Some of them noticed that their pulse was somewhat constant and always available so they used it. Now, back then, things like hours, minutes, and seconds were not firmly defined. The day was, for some reason (that's another discussion) thought of in terms of 24 hours, but a summer day had longer hours because that was 12 hours from sunrise to sunset. And the summer, night hours were shorter. And winter reversed that with it's shorter days and longer nights Minutes were probably not even thought of early on in this process.

    But if the beat of the philosopher's heart was to become one second, then there were around 3600 heart beats in an average hour. Not that anyone thought of it that way at first, but still, that number was about right. So when those philosophers and tinkers started to make clocks, they already had the variable sized hours and the human pulse for the second. Now 3600 is an awful large number to display on a clock face, so it needed to be divided into smaller unit(s). 3600 = 60 X 60: That's real even and bingo, the minute was born. This had several advantages. First, clocks needed gears and you can divide the seconds by 60 twice with the SAME pair of gears. That appeals to anyone who is making the parts. And 60 is also a number with a lot of prime factors: 60 = 2 x 2 x 3 x 5. So it is easy to work with when further subdividing the time interval. You can easily get halves, thirds, fourths, fifths, sixths, tenths, etc. No other relatively small (less than 100) number of divisions has all of the first six integers (1 to 6) as it's factors. So 60 minutes to an hour and 60 seconds to a minute is a reasonable choice.

    OK, but we were talking about angles, not time.

    The earth is a sphere, well pretty close anyway. And it revolves in 24 hours (above). One revolution and one circle are about the same thing. So we have 24 hours x 60 minutes x 60 seconds in time measure for the Earth's single rotation. And again, those philosophers liked to use numbers that could be divided by a lot of factors so 60 would have a lot of appeal to them. The hexacontade, which had 60 divisions, is a unit used by Eratosthenes. However, 60 divisions is a bit on the coarse side and the guys who were surveying land or hurling stones at castle walls from catapults or steering ships on the ocean would want something finer. Why they did not use 24 x 60 = 1440, I can't say. Perhaps that was still a bit too many. Perhaps some did, I don't know. But 6 x 60 = 360 seems to have caught on. 360 divisions were probably around the level of accuracy that ancient devices could measure and/or use for aiming things. And that added two more simple factors to the list of prime factors: 2 and 3. It's prime factors are 2 x 2 x 2 x 3 x 3 x 5 and it can be evenly divided by: 2, 3, 4, 5, 6, 8, 9, 10, 12, 15, 18, 20, 24, 30, 36, 40, 45, 60, 72, 90, 120, 180, and of course, 360. They loved it.



    Anyway, just like the spacing of our railroad tracks can be traced back to the ancient Roman cart makers, I suspect that 360 degrees in a circle can be traced back to ancient philosophers using their heart beat for a measure of short time intervals.

    And also for their love of numbers that can be evenly divided by a lot of factors. This is one drawback of the metric system, which is based on the human hands having ten fingers (thumbs included). But 10 has fewer factors than numbers like 12. So 10 of anything can only be divided by 2 or 5 while 12 can be divided by 2, 3, 4, and 6. Put that in your metric pipe and smoke it. Incidentally the Grad, which is 1/400th of a circle was an attempt at creating a metric unit of angle. It has 100 Grads in a right angle. And no one whom I have ever met has ever used it. There really is some sense to the older, more divisible English units.




    Quote Originally Posted by Yan Wo View Post
    Very interesting question! And it begs the question, "Why does metric use 360 degrees?" Why not 100 or 1000?

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    Quote Originally Posted by Larry Dickman View Post
    so if the metric system is so great, why don't we have metric time?

    There are two types of countries in the world.

    1) Those that use the metric system.
    2) those that went to the moon.

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    Well this got interesting. thanks for the replys

    Dave

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    I have wondered about flare fittings being 82° & 90°. 82° is used on airplanes that use aluminum tubing. I don't KNOW the reason, but it sounds reasonable that the 82° flare would be less likely to cause cracking when making a flare on the end of a piece of tubing than a 90° flare. Just my guess.

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    Quote Originally Posted by steve45 View Post
    I have wondered about flare fittings being 82° & 90°. 82° is used on airplanes that use aluminum tubing. I don't KNOW the reason, but it sounds reasonable that the 82° flare would be less likely to cause cracking when making a flare on the end of a piece of tubing than a 90° flare. Just my guess.
    Are you sure? Please explain the 37 degree angle of JIC/AN fittings?

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    Lots of 37 degree jic/an fittings on the airplane parts we make.

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    Quote Originally Posted by as9100d View Post
    Lots of 37 degree jic/an fittings on the airplane parts we make.
    Exactly, that is my point.

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    I once read that the 37 deg angle was derived as a result of testing by the military engineers to determine the best mix of sealing ability, assembly/disassembly, and some other factors I've forgotten. After all, a long, skinny taper would seal like crazy but you'd never get it apart. No taper would come apart easily but wouldn't seal worth a durn.

    As for the metric system, it is a soul-less conundrum of units that serve only to confuse and abrade the human mind. Who is good with the metric system? Robots. The robots that will someday take over the Earth.

    What kind of man would sidle up to his friends and tell them in quiet confidence that the night prior he gave his woman "all 254 millimeters"? The kind of man who would rather see less football and more figure skating on TV during the cold months, that's who.

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    Pure poetry, Greg.

    May there be a pox on the metric system.

    Sent from my SM-G973U using Tapatalk

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