Metalwork - Assembly - Soldering

What is Soft Soldering ?

Soft Soldering is a method of filling gaps or Permanently joining metals that will undergo only light stresses, at relatively low temperatures. The metals we are concerned about are Copper and Brass and the temperatures involved in Soft Soldering are generally below 400°C. A Filler metal, based on Tin, with a melting temperature lower than the metal pieces to be joined, is melted and allowed to flow into the joint, which on cooling hardens. Soldering is a bit like gluing but it differs in that there is a small bit alloying between the metals to be joined and the solder at the surfaces that come into contact with eachother. When Soldering is done well it also provides a water and gas seal at the joint.

Other similar permantent joining methods are Brazing and Welding.

Brazing involves higher temperatures than Soft Soldering and is used where a much stronger joint is required. Brass is used as the basis of the filler material. In Metalwork it is genarally used to join Steel. Brazing temperatures require the use of an Oxy-Acetylene Torch. (Brazing will be covered on another page at a later date.)

Finally there is Welding. With Soft Soldering and Brazing there is no melting of the base metal. With Welding the base metal is melted and a filler metal may be used to add further strength to the joint. Welding is used where a high strength joint is required. (Welding is not on the Junior Cert. course).

Soft Soldering has two main purposes are far as you are concerned at this stage. To join pieces of sheet metal or to join electrical components. We only deal with Soldering of sheet metal here on this page and electrical soldering will be dealt with at a later stage on another page.

Health & Safety

As with a lot of processes in the Metalwork room, Health and Safety is very important. Soldering requires the use of heat up to 400°C and so heat / fire resistant gloves are a must to prevent accidental burning. If possible it would also be good to wear overalls of some description to protect your clothes.

The Soldering process also involves the use of a mild acid, called Flux. As a result you should also wear goggles to protect your eyes from accidental splashing. The gloves will protect your hands from the Flux and the overalls your clothes.

You may need to move hot pieces of metal as well so employ the use of tongs and be very careful of people around you. Also, and I really hope I don't have to say this, but ..... , hot metals and wood / paper do not go well together so please be very careful where you put down your metal pieces while Soldering.


Main Tools

There are many different ways to solder, depending on what you are trying to join and how you like to go about it. Below are some of the main tools you will probably use.

Soldering Irons

Soldering Irons are used to store and apply heat. They may be heated in a Soldering Stove or using a Gas Torch. The Bit is made from copper as it is such a good conductor of heat and the handle is usually made from wood as it is a good insulator. The soldering iron on top, to the left is called a Straight Bit Soldering Iron and below it is a Hatchet Bit Soldering Iron. The Straight Bit Soldering Iron is the most commonly used and the Hatchet Bit Soldering Iron is used in awkward to reach areas. Both come in a variety of sizes depending on the work being done. Larger soldering irons will store more heat.

Soldering Stove

The Soldering Stove is used to heat Soldering Irons and to keep them heated between uses. It can hold multiple Soldering Irons at the one time allowing for continuous soldering without having to wait for an Iron to heat up. They use gas to heat the Soldering Irons.

Gas Torch

The Gas Torch can also be used in Soldering, either as the heater of the Soldering Irons above or as the actual applier of heat to the parts to be soldered together.

If the Gas Torch is to be used to heat the Soldering Iron care should be taken to get the right temperature. You can tell the soldering Iron has reached the right temperature when the flame just turns a light green.

Using the Gas Torch without the Soldering Irons takes a bit of skill to get the temperatures of the parts to be soldered right. Don't heat the joint first, rather heat away from the joint so that the part holds some of the heat.

When soldering a Lap Joint, (more below), a Gas Torch comes in very handy as it is an easier method to get the heat to the solder than using Soldering Irons.

Remember, when lighting a Gas Torch make sure it is pointing away from you or anyone else. Fire treated without respect can lead to you having a bad day.

Eelectric Soldering Irons

In this day and age, Electric Soldering Irons have taken over from normal old style Soldering Irons to a large extent. Their ease of use and wide range of power make them very suitable for the job. The bit is also replaceable with new bits or different shaped bits.

They are very similar to the Soldering Irons used in electronics works but they are a lot larger and more powerful, usually in the 100s of Watts range.

What tools you use when soldering will be determined by the work you are doing and your own style. Each has advantages over the other types depending on the situation and your skill. With practice, effort and thinking you should become quite good at using all types.


mechanical / chemical
emery paper / wire brush
flux active / passive


made from / lead removed
shape / type - bars/ingots wire
melting point

Soldering Process

step by step

Types of Joint