Soldering 8 Gauge Copper Wire

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I'm in a bit of a situation with a art sculpture I'm trying to make.

I'm making a sulpture of a ferris wheel out of 8 and 12 gauge enamel-coated solid core copper wire, the kind used for winding large transformers. I'm having a real hard time soldering it though. I don't want to damage too much of the enamel so I can't very well solder it with a blowtorch, and I've tried using silver solder and lead-free tinning flux, but nothing will let me solder with any amount of strength. At best I can get some solder adhering to one side of the copper but not bridging the two together. My Iron at 850 degrees F seems to have a hard time melting the silver solder. The only part that liquifies is about 1mm around the tip, thats it. It instantly solidifies if I remove the iron.

Anyone have any ideas about what I'm doing wrong?
 
My 100W Weller iron will solder 14 gauge stranded using 70-30 lead-tin (I know, not EF) I can solder this to plugs & connectors etc. no problem.

Under 10 gauge solid copper is a real heatsink and will suck the life out of a wimpy iron. Using fancy solder with higher melting point won't help. You need a powerful iron to deliver enough heat to do the joint quickly and prevent damage.

Anyone here in the power industry can advise? Is it better to use crimps? Or is it more like welding?
 
I'm not sure if I read anywhere that you are REMOVING the enamel for a sufficient length along the wire. I usually do this with a Dremel and the appropriate grinding attachment. Another option is a solder pot. The insulation will fail at 500-600degrees F. Even if you choose to mechanically remove the coating first, the solder pot will gracefully coat or "tin" the desired joint surface (don't forget to use flux on the wire first, and use good ventilation). Tinning is an alloying process between the native copper of the wire and the chosen solder formulation. It usually occurs at a significantly higher temperature than the melting point of the solder. This is one reason you are using an 800F iron on solder that melts below 400F. Another is the dynamic thermal reservoir that starts at a higher point if you idle your iron hot. Always be sure to add solder to your iron to make a liquid bump (not so much it wants to fall off!) before applying it to the work; this helps make a larger contact patch initially to transfer heat at a greater rate than a point contact.

It helps to imagine the heat flowing into your work as a three dimensional figure, like a mushroom growing in reverse below the surface. Once your iron contacts the copper, a bloom starts at that point into the material. Picture putting a coke bottle full of dye into a tub of water. The dye leaves the bottle gradually as a hemisphere, and the water replaces the coke. Use a puny iron vs. a large chunk of metal and you get uneven heating. I have the best success using two normal 30-50W irons on opposite ends of the desired joint, so the twin hot spots can meet in the middle, as a figure eight. This reduces the thermal gradient through the work piece, and allows surface temperatures to climb high enough to promote tinning without prior pre-tinning. It sounds like a 3-handed process, but with practice you can feed both solder and hold an iron with one hand, and "pinch" the work from the other side or with the 2nd iron in the other hand.

A new solder pot can set you back over $300 bones, but check eBay, I've seen ‘em for $50 and it will really be your friend for multiple wire preparation.
 
Check out the Weller Marksman soldering irons. I have the SP-80 and it does 10 ga with no problems. They go to higher wattages which is more important than temperature for your application. They are inexpensive. I got mine in the plumbing section of the local hardware store.

http://www.cooperhandtools.com/brands/weller/index.cfm?model_list=1&att_id=WEL002&att1=Soldering%20Irons%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20&att2=Consumer%20Soldering%20Iron%20Kits%20%20
 
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