After reading this, maybe this is why so many people have problems getting a good solder joint. 60/40 solder? Why would you use that on anything but a physically solid non-movable joint? Larry even mentions the advantage of 63/37 - it’s eutectic, meaning is goes directly from melted to frozen withoout an intermediate stage. Movement befoore the solder freezes is the primary cause of a ‘cold’ joint where contact can be poor even though it looks ok at casual inspection. Since 60/40 has a short in-between phase, it’s easier for this to happen.
It used to be very obvious - with leaded solder, either 60/40 or 63/37, if the joint is good, it tends to be very shiny. A dull looking solder fillet indicates a cold joint. With lead-free solders, they ALL tend to look dull.
The kicker is where he says that 60/40 is the most common solder in model railroading. Is it truly, even today? If all you’ve ever used is 60/40, try some 63/37. I think you’ll like it. 60/40 is fine for plumbing - you heat up the pipe with your torch, flow on the solder, and let it cool. It doesn’t get moved because, who’s going to touch the pipe right after you took the torch of fit? And the fittings generally go together relatively snuggly. But hooking up some small wires, where even a breeze can cause movement, not to mention being less than 100% steady with the hand holding the wire in place - 63/37 will make a big difference in ease of soldering.
That’s my story and I’m sticking to it…
–Randy