The study visit and joining methods

Methods of joining parts fall into two groups depending on whether the item can be taken apart. Separable joints (screw, bolt and nut, wood screw) can be taken apart without damage, while non-separable joints (rivet, welding, soldering, gluing) are damaged when separated. By mobility a joint can be fixed (the parts do not shift against each other, for example a tightened bolt), movable (the parts rotate or slide freely, for example a wheel axle) or semi-movable (movement limited to a certain angle or distance, for example a door hinge whose opening is limited). The choice of method takes into account the item’s purpose, the type of material, the load, whether it must be taken apart, and cost. A rivet is set with a hammer and a special tool; in welding the edges of the parts are melted and fuse together; in soldering the parts themselves do not melt — a solder (a tin-lead or tin-based alloy) that melts at a much lower temperature than they do is run between them. For gluing, the type of glue is chosen to suit the material and the room is ventilated, because the vapour of many glues is harmful. Welding and soldering are done only under the supervision of the teacher or a qualified master, with a protective mask, gloves and ventilation; looking straight at the welding arc damages the eyes, and a soldering iron stays hot and burns. Such work must never be done alone at home.