Hi,
No matter how you do it, you have two wires floating in a pool of solidified solder at the end of a solder job. It might make you feel better to mechanically twist things together, but it ain't much of a connection at the molecular level. Join two pieces of copper together, get out your soldering iron, get Tim the Tool-man to rewire your soldering iron so it puts out double the output, and let us know how long it takes to melt that copper together without solder. Then think how badly you damaged the structure of the copper trying to melt it together, like super-oxidation from prolonged heat, and uptake of impurites.
Got any idea of what the melting point of copper is?
1984.32 °F
Cheap soldering irons might go 700-800 degrees. So to make your electrically clean splice, you have to rely on a good solder connection. The mecahnical twisting you might be doing is just keeping the solder from penetrating well. Solder is your friend! Good solder is a good friend. More Silver in your Solder, the better the conductivity. The higher the Silver content, the harder the solder is to work with.
Hope this helps.
Ohh, you don't need to twist stuff together. You should be able to pick up things with your soldered wire once it's cooled. I always give mine a tug after they're done.
After all this I didn't answer your original question! Tinning does a lot of things. First the Flux flows from the solder and cleans the wire end. You should have mechanically cleaned it already, the rosin is a chemical etching of the surface. Then I tin the other end, if it's a surface pad on a PCB. Then make sure you have a tinned soldering iron tip, VERY IMPORTANT. So now you have three surfaces with solder on them already.
1) Soldering iron
2) Wire end
3) Other wire end, RCA Jack, PCB Pad, or whatever
So you touch the two wire end together, twist a little so they will hold together, not much though! Put iron to the joint, watch solder flow, and NOW bring in the solder. Once you get this down, you'll be surprised how fast it is, and how little heat you put into what is being soldered.
The prep work is where it all is in soldering. Mechanical cleaning, and tinning. Then the Solder job takes litterally 1-2 seconds of heat.