Soldering Technique

[Jim Kottkamp]

I wanted to share my techniques on soldering.  This will bring a few grins; I have a high tech adjustable soldering iron that I use mostly for electrical connections, but, 95% of all my soldering is accomplished using an old Benzomatic plumbing torch (I also have a small mini torch for job requiring intense heat in a small area).  The lighter next to the torch ran out of gas 4 years ago but the spark generator still works and that's all you need to light the torch.  I can turn the flame down on the torch to a whisper for really small items to prevent overheating.  I use Silver Solder and liquid flux purchased from Micro-Mark.  It is strong enough to withstand stresses in most modeling applications.

Soldering is all about controlling where the solder goes and how much is needed – no more, no less.
 
The technique is to align the cleaned parts being soldered, apply the liquid solder flux, cut a small bit of solder, placing it next to the joint to be soldered and then apply heat.  If you get too much flux on the part it will bubble and the tiny bit of solder will fly off.  To prevent this from happening, tear off a small piece of paper towel and dab it on the joint to absorb excess flux.  The solder will melt and flow right into the joint.  This controls the amount of solder in the joint and prevents problems with excessive solder needing to be sanded or filed off later.  If more solder is needed, I cut off another small bit of solder and re-heat.

Let me define a "small bit" of solder.  The Micro-Mark solder is 3/32 in diameter (1.2mm).  For small parts I will cut off a 3/32 or 1/16 thick piece of solder with a #11 blade.  For really small parts this gets cut in half or 1/4 –sized pieces.

You also need to think about the sequence of soldered items.  In the below piping example, I started with the union, and short piece of pipe, and then added the elbow.
If piping needs to be added to a finished boiler, you can solder in place as long as you have wet paper towels in place.

Please see the next posting for more photos...

[Jim Kottkamp]

With complex jobs, copious amounts of wet paper towels can be used to prevent other solder joints from melting.  I've attached a few photos to show how this works.
 
There is one photo which shows a steam engine boiler repair.  The engine was dropped and the bottom boiler seam split open.  This required both a lot of wet paper towels and considerable bracing to hold the curved support on the inside of the boiler seam.  A lot of heat was required for this repair, but the seam has held nicely and only minor repainting was required after the heat was applied.

The boiler support sequence shows the 2 stages required to complete the installation.  First a brass support was soldered to the original frame.  Then the fabricated boiler support was soldered to the above brass support to complete the job.

One final photo shows soldering a valve in place on a pipe.

[Ray Dunakin]

Very helpful and interesting!

[Lawton Maner]

One trick to contain the solder where you want it to stay is to apply an anti-flux on either side of the part being soldered.  I have used yellow ochre for years.  It comes as a powder and is mixed into a paste with either water or methanol and applied (I use a flat toothpick) to contain solder flow.  Another use is as a weathering powder representing old rust.