We have been approached on several occasions regarding how to carry out the successful soldering of structural components i.e. undercarriages & cabane structures from piano wire or other solder-able metals. We have set out to explain what basically happens to create a successful soldered joint as we feel that if you understand what is happening & why, you will very likely make a more successful job of soldering.

There are 3 main rules to be observed when undertaking soldering tasks; 1) the pieces to be soldered must be completely clean & free from corrosion, oil or grease. 2) a good quality flux must be used for that type of metal to be joined. 3) the job, or parts to be soldered, must become as hot as the melting point of the solder BUT NO HOTTER in order to obtain the correct adhesion of the solder to the metal.

Below is a simple diagram to give a basic idea of what a soldered joint is.

Try to imagine the atomic surface structure of the metal being soldered and that of the solder itself.

The structures here in blue represent the atoms in the solder, while those in black represent the metal to be soldered. You will notice that the orbits of the electrons  in the blue atoms are actually interlocked with those of the black atoms in an apparent chain link formation. This is because unlike welding, these are two dissimilar metals that will not intermix, but they will in many cases contaminate each other at the surface by this atomic interlocking.

The heating process not only melts the solder, it also causes the molecular and atomic structure to leap about "so to speak" within the metal. This becomes more pronounced at the metal's surface, both of the solder and the metal being soldered which now means that the fluidity of the solder can now readily & easily intermingle its atomic structure with its new host.

When joining piano wire components, they must always be bound together neatly & tightly with copper wire at the joint (after cleaning) and then flux applied prior to heating up with a blow torch or a LARGE soldering iron. When using a blowtorch, only use the tip of the flame as this has no more oxygen in it as well as being the hottest part of the flame. Do not overheat the joint, push the solder into or onto the joint (the temperature of the joint itself should be melting the solder, not the direct heat of the blowtorch). If the joint becomes discolored i.e. blackening occurs, it is very likely that the solder will not take to it as this joint has been over heated. The only way to resolve this is to strip the joint down, clean it up thoroughly and start again. Overheating causes the surface of the metal to become oxidized and burned rendering adhesion impossible without cleaning. No amount of  flux on a blackened joint will result in a good joint.

A good quality flux for soldering steel components is Bakers soldering fluid (available from good hardware stores or plumbers merchants) wash the parts well with soapy water after soldering, DO NOT use this fluid on electrical joints as it is very corrosive. If this is not available, us a good quality plumbers flux.

Happy soldering & we hope this info is of help!!!

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