How to Solder: Great Tips on Soldering for Beginners

Learn the basics of soldering to help with projects around the farm.

| November 15, 2012

  • Siphoned Soldering Heat
    Whenever an electronic component looks as if it might be cooked, grab its leads with pliers to siphon off soldering heat.  
    Photo Courtesy Fox Chapel Publishing
  • Farm And Workshop Welding By Andrew Pearce
    “Farm and Workshop Welding” by Andrew Pearce instructs the novice metal worker on how to weld, cut or shape metal — a practical guide to have around a homestead. 
    Cover Courtesy Fox Chapel Publishing
  • Clean Bit
    No matter how the bit is heated, it must be kept clean. The dirty-looking, oxide-covered specimen won’t transfer heat properly and brings contamination to the joint. File it or wire brush it, then keep it wholesome during work by wiping it on a damp cloth.  Any bit must be tinned before use: fluxed, covered with a thin coat of fresh solder and refluxed to leave it shining silver (next photo).  
    Photo Courtesy Fox Chapel Publishing
  • Soldering Irons
    Traditional soldering irons hold the bit in a steel shaft. Heat comes from a separate flame.  
    Photo Courtesy Fox Chapel Publishing
  • Refluxed Bit
    No matter how the bit is heated, it must be kept clean. The dirty-looking, oxide-covered specimen (previous photo) won’t transfer heat properly and brings contamination to the joint. File it or wire brush it, then keep it wholesome during work by wiping it on a damp cloth.  Any bit must be tinned before use: fluxed, covered with a thin coat of fresh solder and refluxed to leave it shining silver. 
    Photo Courtesy Fox Chapel Publishing
  • Three Soldering Irons
    Three types of electrically heated soldering iron. The 20W miniature variety (right) is, naturally, for small jobs. The much bigger version (center) has a jumbo-sized tip, giving a good heat reservoir for big work. The 100W instant heat gun (left) is a good all-round tool, coming quickly to temperature and usually taking interchangeable tips.  
    Photo Courtesy Fox Chapel Publishing
  • Self-Contained Gas Iron
    Modern self-contained gas irons are ideal for jobs in the cab. A good brand like this Antex generates plenty of heat. Kit’s attachments extend usefulness into jobs like cutting/sealing polyprop rope. Liquid butane is held in the handle/reservoir.  
    Photo Courtesy Fox Chapel Publishing
  • Using Metal As Glue
    Soldering uses soft metal alloy as a glue. Glued joints are weak when peeled (A); think of pulling off a sticking plaster. Joints loaded in shear are much stronger (B). So a lasting soldered joint is one with a big surface area which will only have to cope with straight pulling loads.  
    Illustration Courtesy Fox Chapel Publishing
  • Soldering Tools
    Peripherals for soldering. Resin flux and cored solder (center) are primarily for electrical work. Acid flux (left) scours surfaces and will corrode if not washed off: it’s generally used with plain solder (right and front) on plumbing and sheet work. The gas blowtorch (top) has replaced the blowlamp for heating traditional irons. 
    Photo Courtesy Fox Chapel Publishing

  • Siphoned Soldering Heat
  • Farm And Workshop Welding By Andrew Pearce
  • Clean Bit
  • Soldering Irons
  • Refluxed Bit
  • Three Soldering Irons
  • Self-Contained Gas Iron
  • Using Metal As Glue
  • Soldering Tools

Almost anyone can learn the craft of welding, Andrew Pearce argues in his straightforward and handy guide to do-it-yourself metal work, Farm and Workshop Welding (Fox Chapel Publishing, 2012). In this excerpt from chapter 7, Pearce gives detailed instructions on how to get started in soldering, complete with tips on how to overcome common problems with welding techniques. 

Buy this book from the MOTHER EARTH NEWS store: Farm and Workshop Welding.

Soldering is a lower-temperature version of bronze brazing, using filler alloys that are less physically strong and melt at lower temperatures. As with bronze work, the bond between metals is not made by fusion. Instead it’s formed partly by the filler hooking into the tiny hills and valleys of the joint metal surfaces, but mainly from the solder dissolving (not melting) into a very shallow surface layer of the joint. So for soldering to work, it must have free access to ultra-clean parent metals. For this reason flux is always used as a chemical backup to mechanical surface cleaning.

Silver soldering suits dissimilar metals and is generally used with capillary joints, leaving little or no external build-up of filler. The filler itself is a fairly expensive mix of copper, zinc and silver which, being tougher than soft solder yet still electrically conductive, is useful where a joint must stand moderate heat and vibration. Electrical heating elements are often silver-soldered. The temperatures needed for silver soldering can only be achieved by a flame (or arc), not an iron. If the work is not too big it can be laid on a firebrick hearth and heated with a small butane torch.



How to Solder: About Solder Flux

Buy the flux when you buy the silver solder. Take great care over preparation. Pre-flux the joint, then dip the rod in flux. Work quickly so the flame does not tarnish the cleaned surfaces. Let the silver solder melt with the heat of the joint metal, not directly by the flame. After soldering the flux residue can be washed off with hot water. 

Soft soldering is the much more common form, used on heat-sensitive items or on joints that don’t need much mechanical strength. Filler metal melts at 482ºF (250ºC) or below, so the necessary heat can be transferred from an iron. The alloy is a lead-tin mix, often spiced with antimony. Soft-soldered joints are everywhere — in vehicle wiring, radiator header tanks, plumbing joints in copper pipe. Different metals can be joined too, like copper to steel.






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