How To Solder Copper
Note: Don't solder copper strips if you will be doing a flame coloration on them later. The heat of the flame will make all your solder joints come apart. You must braze these strips instead.
Soldering is similar to brazing and welding but at much lower temperatures. Brazing is usually in the 1050 – 1150 F range. Soldering is usually in the 350-550 F range.
Soldering uses plumbing solder, which is usually a tin-antimony alloy with a little silver added to it for better wetting, adhesion and rigidity. I buy it in the plumbing section at Lowe's or Home Depot.
Soldering also uses a flux, which cleans the metal, and creates a gas that shields the metal from oxygen while you are soldering. Oxygen is the enemy of effective soldering. You will notice that the solder won’t stick to unfluxed copper. Flux is essential to effective soldering. We prefer to use Sterling flux because it is water-soluble, easy to wash off and cleans the metal better than the vaseline-based flux, such as Oatey Flux. You can glob on this flux – more seems to work better and cleans the metal better.
You’ll need the Meco Torch with a #2 tip for soldering copper strips together. A Harris torch is also fine - just heavier.
To solder a copper weaving to copper pipe you will need a #3 or #4 tip with most of the heat going on to the pipe and only a very little going onto the copper weaving.
Set the Acetylene regulator at about 2 psi, the oxygen regulator at about 5 psi
Adjust the torch so that it is quiet, with no whistle, and about a 1” cone. Soldering works best with a minimum of oxygen. You don't want a tiny hot flame.
I am right-handed so my right hand is my 'smart' hand. When I am soldering, I usually hold the torch in my left hand. In my right fist I hold a 9" copper pipe for pressing on the soldered join, and between my right thumb and forefinger I am holding the spool of solder with 6-12" of solder sticking out. I am wearing leather work gloves.
With copper strips, you need to put the heat on the junction for 1-2 seconds at most. With copper pipe, it may take 3-5 seconds to get it hot enough.
Don’t use the torch to melt the solder – the hot metal has to melt the solder. Put the torch near the copper for 1-2 seconds, then pull it away 10-12" while you touch the solder to the heated metal.
If the metal isn’t hot enough to melt the solder, it won’t bond with the solder. Pull the solder away, go back in close for another second or so, then pull away the torch again and touch the solder to the heated area.
Longer times heating the copper strips doesn’t work – you’ll burn off the flux, the copper will warp, the solder will run everywhere and not stick and it will look bad.
Touch the solder exactly on the junction - presumably it melts. Then reheat the junction briefly – for about ½ second. You want the solder to get sucked under the join. Then remove the heat and immediately put the copper pipe (in your right fist) on the join and compress it. Continue pressing down on the join for a few seconds with the copper pipe - or you can use a heavy steel weight or a brick. To cool it faster, you can blow on it. You want to keep the join compressed until you see the molten solder 'freeze'. It will actually change color slightly.
If you remove the weight from the join too soon, before it has ‘frozen’, it will gap open slightly, weakening the join. You will have to go back and resolder the join. Hold it down until it has ‘frozen’.
Test your solder joins with a knife to see if you can get the blade under the join, or pry it up.
A good solder join is small, flat, silvery in color and the two metal parts it joins should be as close together as possible. If it is dull gray and appears, under the magnifying glass, to have tiny holes in it (porosity) then you have overheated the solder. It will probably hold, but try and avoid doing this.
After all the soldering is completed, wash off the flux with Dawn and a scrub brush, rinse and let dry.
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