Wednesday, December 30, 2009

Copper key fobs

I found some scraps of 12/2 and 14/2 electrical wire while cleaning out the attic, and thought I'd try to make use of it. Short scraps are useless for house wiring.

First need to strip off the plastic insulation.

The grounding wire is bare copper. It's what I will use. Pretty, huh.

A piece of aluminum makes a mandrel, chucked in my cordless drill. I clamped it in my vice and spun it on low speed. I keep tension on the wire using a gloved hand.

Next I use a dremel to cut the rings while they are still on the mandrel. A jeweler's saw would work better since it has a thinner kerf. The kerf with the dremel is wide so when opened or closed the rings do not make perfect circles, but no matter. The copper is too soft for aviation snips, but wire cutter probably would have worked.

The rings have a 3/8" inner diameter (ID). 12 AWG is .081", so I want to calculate the aspect ratio. AR = ID / WD = .375/.081 = 4.6. Full Persian requires at least 5.5, which explains why I was having trouble with the first fob - its practically rigid!

The 14-gauge rings have an AR of 5.9 so work fine in Full Persian. I enjoy working with these copper rings because they are dead soft, similar to silver. Titanium and stainless steel do not share this characteristic.


benthomasson said...

Can copper be heat treated to increase hardness?

Digital Twilight said...

Copper will harden through cold working. This means if it is repeatedly bent, hammered, etc, it will get harder. The easiest way to make ti harder would be to wind and unwind it on a spool several times, or between two spools several times. This will make it significantly harder.

Heating the rings to red hot and quenching in water will anneal them, to make them harder you would need to heat them to red hot and let them cool very slowly. The only problem with this is in the presence of oxygen the copper will develop a layer of scale. This would be difficult to remove from the finished rings.