START­ING OUT…

Model Rail (UK) - - Workbench -

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.”

Dave’s Ex­pert Tip “If you can, make grav­ity work for you. Try and solder ‘down­hill’ if you can - most solder has got lead in and lead will al­ways drop.” Dave’s Ex­pert Tip “Heat is the beauty of sol­der­ing. If you make a mis­take, add heat and you can cor­rect it. Can you do that with glue? No. You’d have to pull it all apart, clean it all up and start again. That is why sol­der­ing is so good.”

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