How far can a penny go these days?

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George Schmermund
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How far can a penny go these days?

Post by George Schmermund » Sun May 23, 2010 1:17 am

I decided to dust off the micro-cyclotron project today and thought I'd experiment with making some small parts (update report soon to follow). As usual, I got distracted and veered off course. A roll mill and precision saw can have some fun in them after a couple of beers. I realize that most of you here roll your own foils and cut your own thin sections, but for those who don't I offer the following as a practical demonstration.

The rolled penny appears to be mostly copper. As can be seen, the thickness at the tip is 19 microns. It levels off to about 50 microns in the rest of the rolled part. The coin was not annealed for any of this, so it would have gotten thinner through the whole rolled section if it had been annealed.

The penny that has been sectioned is newer and has a zinc core. The dime that has been cut in half is a newer one and has the copper core. The saw can also do thin sections with hard stuff that can't be rolled easily (like tungsten and sapphire) and will make slices down to foil thicknesses.

Never judge a coin by its exterior!
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penny roll.JPG
penny roll.JPG (31.83 KiB) Viewed 1820 times
Anything obvious in high vacuum is probably wrong.

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Doug Coulter
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Re: How far can a penny go these days?

Post by Doug Coulter » Sun May 23, 2010 4:10 pm

I don't recall the exact date where all pennies switched to zinc core to make them cost less than a penny to make (now they cost more than a penny even with that), but it was awhile back, only the pretty old ones are the copper alloy.

Another fun trick is to knick one with a file, and drop it in a beaker of HCL. Come back later and you have a nice perfect hollow penny shell. Cheap source of fairly good quality of zinc chloride too.
Why guess when you can know? Measure!

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Richard Hull
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Re: How far can a penny go these days?

Post by Richard Hull » Mon May 24, 2010 3:55 pm

1983 was the year we went completely from a bronze, (~95% copper), penny to a pure zinc, copper clad penny. The clading is thinner than a sheet of toilet tissue. the net result is a 97.5% zinc penny by weight. Note* in 1982 a production mix of the two types of coins is claimed. If so, then 1981 is the last year for a warranted, pure bronze penny.

In 1943 we had a single year of steel pennies that were zinc clad. From about 1944 to 1946 we used an oddball alloy of brass and copper, reclaiming shell casing metal from WWII expended ammunition.

Copper was cheap in 1938 at ~10cents/lb. However, for a brief moment, recently, it was over $4.00/lb! Now it hovers around $3.00/lb.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Doug Coulter
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Re: How far can a penny go these days?

Post by Doug Coulter » Mon May 24, 2010 4:34 pm

Thanks for the numismatics, they had slipped my mind, but I had my wife go though the penny jug last year and separate them all out for that reason. Still a goodly number of the old type around. Seems like people keep them forever, no point putting a burden on your pocket carrying them anymore.

Back when I was a kid and collecting coins, I remember there was a scam where people copper plated those steel war pennies and tried to pass them off as super rare. Easy to detect, of course, with a magnet.

I make my living mostly trading "the metal that has a PhD in economics" so copper is kind of something I keep up on, otherwise. It had been going up nicely with the "recovery" but really got "hammered" in this recent downturn....and went below $3 for a little bit. July copper is $3.13 at noon today, up a couple percent from last week. It'll probably fart around in that range for awhile, until something like a real recovery happens, or the worst does instead.

I once bought a few hundred pounds of copper flashing, and it's a premier prototype material around my shop for lots of things. Easy to form, to join, to make air and light tight, great thermal conductivity, electrical and all the good stuff. Not so much fun to machine the stuff in bulk though -
Why guess when you can know? Measure!

Jerry Biehler
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Re: How far can a penny go these days?

Post by Jerry Biehler » Mon May 24, 2010 8:51 pm

Many years ago I built a HF unit for tig welding. Needed two 1/2"-13 threaded copper studs for the secondary connection of the HF transformer. First I tried a die. Yeah right...

Ended up single pointing them on a lathe.

Milk make good cutting fluid for copper. Just make sure you clean up after.

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