STARTING OUT…
Before we reached for the iron and flux, Dave went through a little bit of soldering theory: “When we come to soldering bits of brass together, most people will put a bit of solder here [see Fig 1]. If you press against the upright there [see Fig 2] it will fall apart because there’s no solder there. “We want it to have solder down both sides [see Fig 3]. The material either side of the joint will break before the solder does [see Fig 4].” Dave handed me a pair of pliers and I tried to pull a newly soldered joint apart. As he predicted, the brass snapped above the joint – but the joint remained completely intact.
TINNING
Tinning also works when building kits. The process is simple: flux both pieces, “splosh” solder over the sides and the ends, hold the pieces together and then add heat. The solder will melt, fixing both parts together. Except that it wasn’t working. There wasn’t enough heat at the tip of my iron. Dave suggested using the side of the tip to transfer more heat but it still wasn’t enough. “The solder’s spreading,” Dave observed, “but the iron is sticking to the metal. “What’s happening is that the brass is sucking the heat out of the solder; it’s taking all the heat away. It’s not melting the solder so it’s not flowing.” Dave used a Weller soldering station (see p51), which is able to transfer much more heat. Having re-fluxed the components, I was able to spread a thin layer of solder over both components, before using more flux and reapplying the iron. Said Dave, “Can you see the little meniscus develop between the edge of the tip and the joint? “If you’ve got that meniscus, go back and touch the metal and draw it all the way along the joint and just keep going. When you cut off the end there should only be a little tiny bit of solder. Go around the other side to have a look at it, to see if it’s almost gone through. “Now, it’s worth doing this again but on the other side. A little bit of flux and, just very slowly, start at one end.” Result: I joined two bits of brass together!
WHY TINNING IS GOOD
“Because you tin both parts separately,” Dave explained, “you don’t place as much stress on them. Parts will always expand because of the heat, so each part will expand and cool down before you try to put them together. “If you try to solder fine parts together straight away and, for example, a bit of the solder sticks and the other bit doesn’t, it could distort or kink a part.”
FLUXING THE JOINT
You can, however, save time by soldering two pieces of brass together without tinning. “This time, we’ll add flux to both parts - fluxing the joint so to speak - and solder the two together,” said Dave. “Hold the two pieces together, add flux and then gently introduce the soldering iron. Allow [the joint] to heat up and then gently draw the iron across. Work slowly. You may need to top up just a bit more solder, start halfway down and go forward and backwards so that it keeps the flow going. You’ll end up with just a smear of solder so there’s nothing much to clear away.”