Soldering Brass, Copper and Photo Etch

RESISTANCE SOLDERING

I’ll switch gears here and install the next fitting using resistance soldering methods. This could be done with the standard soldering iron and heat sinks, but I wanted to show one of the benefits of resistance soldering. Additionally, this U-shaped brace is going to be installed with solder paste instead of solder wire. Either would work, but again, I wanted to show you when you can really use the advantages of this medium. Added flux is optional in this instance since the solder paste has a large amount mixed in as the binder for the paste. Pic 44.

I installed a Blu Tack brace at the bottom of the U and made the joint by placing the tweezers on either side of the joint. The resistance caused by the joint itself causes the low voltage, high amperage current flowing through the two sides of the tweezers to generate heat at that joint and melt the solder. Since the heat is centered at the joint between the two pieces, the heating of the adjacent areas is less severe. The closely spaced joints are unaffected by our work and remain solid and shiny. Railroad modelers have used this system for years soldering their brass locomotives together. Pic 45.

Next I will install a small diameter cross brace using resistance soldering and solder paste. Tinning the parts is optional but cleaning is not. The solder paste can be used as an aid to locating the part. It will not secure the part until the solder is melted but it does help keep parts in the general position. This task could just as easily be done by tinning the two pieces, applying flux and heat sinking the surrounding joints to allow use of the conventional soldering iron. Pic 46.

I performed the same process on the both ends of the small crosspiece and got ready to solder the U-brace using solder paste and the conventional soldering iron. Since I could heat both joints on the brace at the same time, using the conventional iron means I have less chance of slipping and moving the joint. Before making the U brace joints, I installed heat sink clips on each side of the area to protect the outboard joints. Heat really only has one conductor to travel on in this instance since I will be touching the joint for less than a second and the clips isolate it well enough that wet Kimwipes are not needed. Pic 47

To demonstrate you can still solder large surfaces even after you have made very small joints, I have cleaned a piece of sheet copper, fluxed and tinned the corners and tinned the ends of the brass rod cross pieces for joining. The flux residue has not been cleaned from either of the pieces yet… Pic 48.

I heat sink each leg and use the resistance soldering hand piece to make each joint. The quick heating of each joint is a real benefit that makes this large surface job easy compared to using the conventional iron and the Kimwipes. Both can still be done, but nobody gets extra credit for doing things the hardest way possible. Pic 49.

I am going to show you how to solder flat surfaces in the next series of pictures. I have cleaned and folded a sheet of copper, applied flux and am about to solder the joint. Pic 50, 51, 52.
Here is the finished joint. Pic 53.
Here I have cleaned and tinned another piece of copper sheet in preparation for soldering the previous part in place. Pic 54.
Here is the soldering action with a clamp in place and using an orangewood stick to help maintain positioning. Pic 55.
Here is the completed joint. Notice the smooth bright fillet along the edge of the joint. Pic 56.
Here is the next folded piece going on. We will solder this on the larger surface and create another long joint. Pic 57.
Here is the tinned and cleaned part ready for install. Pic 58.
Here is the base piece tinned and ready for the next part with heat sinks in place. Pic 59.
Solder bridge in place, joint being made… Pic 60.
Here is the fininshed joint. Note the smooth fillet next to the solder bridge. Pic 61.
Here is the upper joint of the pyramid after being cleaned, fluxed and soldered closed. This was done again with the standard soldering iron. Pic 62.
And to show that small parts can still be added even on large areas with a standard soldering iron and solder paste… Pic 63.
Here is the finished assembly. Pic 64. There’s nothing to it!

Hopefully, this information will help you decide to attack some of those more challenging projects. It is not all inclusive, but it should provide a good foundation for anyone interested in soldering components to make them stronger, cleaner and more realistic.

Here are some of the assemblies I’ve done using these methods for an FT-17: Pic 65, 66, 67, 68, 69.