Wood screws are used to join metal or plastic components to wood, or to join two pieces of wood to make a strong joint.

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1 Página 19 de 236 Components and adhesives The components of a product are the smaller elements or parts which make it up. Examples of components are the nails, screws, hinges or catches that hold the product together. Adhesives are used to join materials together by gluing. Different types of materials and different situations require different adhesives. It's important you learn the type of adhesive, rather than the brand name. Components: Resistant materials components are usually bought ready-made. The most common components you need to know about are nails, screws, hinges and catches. The main types of component are: threaded fastenings, including wood screws, machine screws, nuts and bolts, and self-tapping screws rivets, including hammered rivets and pop rivets hinges, catches and locks knockdown fittings Nails are generally used where appearance is not important, or where a quick job is needed. Panel pins and veneer pins are used to fix backs onto cupboards and bottoms onto boxes. Veneer pins are finer (or thinner) than panel pins. Nails and pins are usually made of mild steel. Wood screws are used to join metal or plastic components to wood, or to join two pieces of wood to make a strong joint. Machine screws have a screw thread to fit into a threaded hole or a hexagonal nut. They can be used to join two or more pieces of metal or plastic. Bolts have a screw thread which fits into a threaded hole or a hexagonal nut, and are normally used to join two or more pieces of metal or plastic. A bolt is only threaded for part of its length. Bolts normally have hexagonal heads.

2 Página 20 de 236 Set screws have a screw thread along the whole or most of their length, and normally have hexagonal heads. Nuts and bolts Bolts are used to join pieces together either permanently or temporarily. Many steel structures, including buildings, are simply bolted together. For example, the Eiffel Tower in Paris was originally a temporary structure and after twenty years it was to be dismantled. For this reason most of the steel components were bolted together. However, the tower has lasted well over a hundred years. Much of the structure of the Empire State Building in the USA is also bolted together. Nuts and bolts can also be used to fix together small structures such as furniture. Nuts and bolts come in many different types and sizes and some are shown below. TYPICAL COACH BOLT The coach bolt has a square collar under the domed head and this locks into the wood when the nut is tightened. A washer is normally placed before the nut to stop it sinking into the wood as it is turned. Two spanners are needed to tighten this nut and bolt. The first spanner fits round the hexagonal head of the bolt and a second spanner is used to tighten the hexagonal nut. ACTIVITY 1. Sketch an hexagonal nut and bolt. Your diagram should show a practical way of using them. 2. Explain why a washer is sometimes used The countersunk machine screw fits level with the surface of the wood/metal/plastic. A screwdriver is used to keep the bolt still whilst the wing nut is tightened by hand.

3 Página 21 de 236 A plain washer prevents the nut sinking into the surface of the wood/plastic/metal If there is a need to prevent A nut and bolt loosening a spring washer is used. Components: Hammered rivets are used to join metal, but are sometimes used on products such as kitchen knives, where a wooden or plastic handle may be riveted to the blade. The soft metal shaft of the rivet is passed through a hole drilled in the material to be fixed. Then, while the head is held tightly in place on the other side, the shaft is hammered flat to form a secure joint. Pop rivets were originally designed for use in the aircraft industry but are now used in many different products. They are often used where there is only access to one side of the material - e.g. fixing to a metal tube. The body of the rivet is inserted into a hole drilled into the material to be fixed, and when the pin is gripped and pulled by a special tool it pulls and expands the body to form a solid joint on both sides of the hole. Pop riveting is a technique that is used to join thin pieces of metal and it can also be used to join plastic sheet. The rivet has two parts; the pin and the rivet. The pop rivet pliers are used to pull the pin through the rivet and as this happens the rivet is deformed slightly so that it joins the metal or plastic pieces. This is explained in detail below. This technique is used where the metal or plastic is thin and where the joint does not have to be very strong. It is ideal for joining aluminium or even thin sheet plastic. 1. The two pieces of plastic or aluminium are drilled to a size slightly larger 2. The pop rivet is passed through both holes in the sheet plastic / aluminium.than the rivet 3. The rivet pliers are pushed on to the pin of the rivet and the handles are pulled together. As this happens the pin head is pulled into the rivet and the end of the rivet is

4 Página 22 de 236 expanded. Eventually the pin will break off leaving the rivet permanently fixed in position holding the two pieces of plastic / aluminium together. Knock down (KD) fittings are used where something has to be taken apart often, or which is designed for assembly by the user, such as kitchen units or self-assembly furniture. They are often plastic fittings which can be joined with one screw or bolt. SMART MATERIALS POLYMORPH SHAPING BY HAND Polymorph is a thermoplastic material that can be shaped and reshaped any number of times. it is normally supplied as granules that look like small plastic beads. In the classroom it can be heated in hot water and when it reaches 62 degrees centigrade the granules form a mass of clear material. When removed from the hot water it can be shaped into almost any form and on cooling it becomes as solid as a material such as nylon. Although expensive, polymorph is suitable for 3D modelling as it can be shaped by hand or pressed into a shape through the use of a mould. Smart materials polymorph - Using a mould A mould can be made by hand by a skilled craftsperson. However, a piece of CAD software such as pro/desktop can be used to design a mould and a CNC machine can then be used to cut / mill the shape. However, polymorph is a material suited to fast prototyping rather than the lengthy use of CAD software and CNC machines. Polymorph is useful because it can be shaped by hand very easily. The advantage of using CAD / CAM is that a more accurate prototype can be made.

5 Página 23 de 236 Adhesives Adhesives are used to join materials by gluing. Different types of adhesives are used for different materials - for example, if a product is to be used outside, then waterproof adhesives should be used. In the exam you should use the name of the type of adhesive, rather than the product name - e.g. PVA glue, not Evostick Resin W. Rules for making a well-glued joint the surfaces to be joined must be clean and free of dust and grease the joints must fit closely together if the adhesive needs to be mixed, this must be done in the correct proportions, and With most adhesives, the joint should be held together by clamps or weights until the glue has dried. Adhesive types The main types of adhesive are PVA (polyvinyl acetate), synthetic resin, epoxy resin, contact adhesive and acrylic cement. The table outlines the different uses of these adhesives Joints Joints between materials can be either temporary or permanent, and may be formed with adhesives, with frame joints 31, brazed or welded joints, or with fastening components such as nails, screws, bolts, and rivets Joints in wood can be with screws, nails, glues and knock-down 32 components, or with frame joints - e.g. butt joints, halving joints, mortice-and-tenon, dovetail, and box joints. Joints in metal can be made with brazing 33, soldering 34, welding 35 or rivets. Joints in plastics can be made with plastic adhesive, rivets, bolts or machine screws. 31 Frame joints: joins in which the components meet al right-angles and fit tightly with each other. 32 Knock-down: joint made up with separate components which are designed to be easily assembled and disassembled. 33 Brazing: joining two metal objects by melting a third metal with a lower melting point between them fusing the two surfaces or edges together. Originally used brass as the filler metal. 34 Soldering: joining two metal objects by melting a softer metal with a lower melting point between them thus fusing the two surfaces or edges together. Soldering is a form of brazing.

6 Página 24 de Types of joint 2. Joining wood 1: screws, nails, glues and knock-downs 3. Joining wood 2: frame joints 4. Joining metal 5. Joining plastics Types of joint: Most products are made from more than one piece of material, so when the product is assembled or fabricated the pieces need to be joined. Joints can be either permanent or temporary, and there are many different types. 35 Welding: joining metals by melting and fusing the adjoining edges or surfaces.