Joining metal

As with wood, there are many ways of joining metal permanently. The method used will depend on the function of the product, the strength needed and the quality of the product.

Brazing and soldering

Brazing is a way of bonding materials (usually metals) by melting a filler metal or alloy between the components you want to join. The filler metals used in brazing usually have melting points between 450°C and 1000°C, but must have a lower melting point than the material being joined. Brazing forms very strong, permanent joints.

Soldering is a type of brazing which works at lower temperatures. Soft soldering is used to make permanent joints between copper, brass, tinplate or light steelwork, and is the normal way of joining electronic circuit components. Soft solder melts at about 200°C. The solder flows into the heated metal along the joint, distributes itself by capillary action, and grips the two pieces together when it all cools. Hard solder melts at 625°C, and is used for stronger joints.

Welding

Welding is different from soldering in that the two pieces of metal are themselves melted along the joints, fusing together as they cool. In oxy-acetylene welding a very hot flame is used. In electric arc welding a spark is used to heat the metal. In both processes a filler rod may used as well to get a really strong joint.

Machine screws and rivets

Machine screws are special screws for joining metal components, which unlike wood screws do not have a tapering core (like bolts, but smaller). Machine screws have to go into a pre-drilled hole in the component which is the right size and which has the correct internal thread.

Rivets are components used for joining metal (and sometimes plastics and plywood). A hole is drilled through both pieces of work, the rivet placed through it, and its end beaten into a dome. A tool called a rivet set or rivet snap is used to to finish the joint off neatly. Some rivets are countersunk.

With most rivets you need to get at both sides of the work to make the joint. Pop rivets enable you to complete the joint while only having access to one side of the work. They are usually used for joining thin sheets together.