standard grade craft & design revision materials

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Standard Grade Craft & Design Revision Materials Slide 2 Coping Saw Coping saws are used to remove complicated shapes and cut curves in wood and plastic. The blade is held in a frame and may be easily replaced if broken. The teeth of the blade point backwards towards the handle. The saw cuts on the pull stroke and not on the forward stroke. This is because the blade is too flexible to be pushed. The blade can be angled in the frame if the frame gets in the way when cutting larger sheet materials. Slide 3 Tenon Saw Tenon saws are used to make straight cuts in wood and occasionally some plastics. This type of saw has a stiff back and is suitable for detailed cuts. The saws without this type of stiff back are more flexible and are designed to cut large panels. The tenon saw is generally used to cut woodwork joints. The tenon saw is used in conjunction with the bench hook. The bench hook is used to support the piece of wood while it is being cut. It hooks onto the edge of a bench. The saw has 12-14 teeth every 25mm. Slide 4 Rip-Saw Large panels or sheets of materials, for example plywood or MDF, require larger ripsaws in order to cut them by hand. Sheets that are small enough may be held in the vice, but larger sheets may need to be supported on special types of portable carpenter's supports called trestles. Ripsaws are used to cut along the grain of large panels of real timber. Panel saws are shorter in length to ripsaws and have finer teeth, 10 teeth every 25mm. Ripsaws have 4-5 teeth every 25mm. Because of its finer teeth and shorter length, the panel saw is suited to thinner wood and sheets of manufactured boards. Slide 5 Sawing An Introduction Sawing is a way of separating the material that is not needed from the material that is. The cut or gap that is produced by the saw is called the kerf. The kerf is usually wider than the saw blade so that the blade does not get stuck when it is cutting through the material. Bending alternative teeth from left to right produces this gap. This bending of the teeth is called the set. Hacksaw blades are normally in the shape of a wavy cutting edge. It is important when cutting to always cut to the outside of the marked line. This side of the line is called the waste side. You must also leave enough room for filing and sanding. The choice of saw depends upon the type of material to be cut. Always use the correct saw. Wood saws like tenon and panel saws are not hard enough to cut through metal. Metal-working saws like hacksaws will cut through wood, but not very effectively. Plastics like acrylic and polystyrene may be cut with coping saws, but it is best to use a craft knife to slice the plastic along a straight line and snap it over a hard edge. Slide 6 Sawing Metal - Hacksaws Hacksaws and junior hacksaws produce straight cuts in metal. Both have replaceable blades held in tension in the saw frame. The teeth face away from the handle and cut on the forward stroke. This is the opposite effect to the coping saw, which cuts on the pull stroke. The lengths of hacksaw blades are between 250mm and 300mm. The saw frames can be adjusted to cater for both sizes. Like the coping saw, the blades can be turned through 90 in the frame. This allows the hacksaw to cut larger sheets of metal. Blades normally have 14, 18, 24 or 32 teeth every 25mm. This is called the pitch of the blade.This is more teeth per blade than the coping saw, tenon saw, panel saw and rip saw. Soft materials require a coarse pitch, less teeth, hard materials, a fine pitch, more teeth. Three teeth should be in contact with the materials at all times. A fine-pitched blade needs to be used for tubes and thin gauge materials. Sheet saws are like panel saws but with a hacksaw blade attached. These types of saws are used to cut sheet metals and plastics. They also cut corrugated sheet. Slide 7 Abrafiles The abrafile has a toothed, circular blade that fits into a frame. Abrafile blades can fit into a hacksaw frame using a pair of adaptors. Coarse, medium and fine grades are available. Abrafiles are used to cut out curves and rounded shapes from sheet metal. Abrafiles are very good at cutting wall tiles. This image shows an abrafile blade in a junior hacksaw frame. Slide 8 Sawing Wood By Machine An electric fret saw has a reciprocating blade built into a frame. This means that the blade moves up and down and is pushed against the material. This type of machine is ideal for fine, detailed shapes and cuts small pieces of flat, sheet materials. It is very good for making jigsaw puzzles. It does not cut thicker materials very well. It can be used to cut plastic; a useful tip is to cover the part to be cut with masking tape to stop the plastic's waste sticking in the cut behind the blade. Slide 9 Mitre Saws Mitre saws have a blade that can be adjusted to any angle. The saw has cramps that allow the material to be fixed to the frame while cutting. The mitre saw may be used to cut 45 corners for picture frames and mitre joints. The blade cuts on the backward stroke. It is possible to buy electrical mitre saws. These are called chopsaws. Slide 10 Jigsaws The image above is of a 'Dewalt' portable jigsaw. It is used to cut out complicated shapes from large sheet materials like plywood and MDF. The blades can be changed to deal with such materials as metal and plastics. This type of saw, like the fretsaw, has a reciprocating blade that moves up and down. Slide 11 Centre Lathe (Metals) When turning materials in a centre lathe: the material to be turned is held in a rotating chuck a cutting tool held in a tool post cuts the material the shape of the cut depends upon the path taken by the tool the material will either be cylindrical in shape or flat Slide 12 Casting Casting is a process where a metal is heated to such a high temperature, it turns to a liquid. We call this a molten state. The metal is poured into a mould, left to cool and removed (in a solid state). When the metal (or plastic) is in this molten state, we say that it has reached its melting point. The temperature depends upon the type of materials used. This is an essential feature in casting and welding. A company called Brambley Furniture produces aluminium cast furniture by traditional methods using sand-casting and hand-carved wooden patterns. Today, aluminium is used rather than iron and each piece is carefully finished in oven-hardened acrylic paint. The image above shows an example of a Brambley garden furniture set. The chairs have been sand-cast from aluminium and finished in an oven-hardened acrylic paint. Details are: Material: aluminium Composition: it is a pure metal Properties: light, soft and malleable. It conducts electricity and heat very easily and can be welded and soldered by a special process. Aluminium is a non-ferrous metal, meaning that it contains no iron and will not corrode and rust if left outside. This is very different from cast steel and iron, which rusts because they are both ferrous metals. Uses: to make boats, aircrafts, railway coaches and foil for packaging and cooking. It may also be used to make engine cylinder heads, pistons, cranks, window frames, saucepans and electrical cables. Slide 13 Manufactured (man Made) Boards Manufactured boards are made from natural timber. Sandwiching thin sheets of wood together called veneers can make manufactured boards. The veneers are glued together and compressed. Taking particles of wood, mixing them with glue, compressing them and applying heat can also make manufactured boards. Very wide boards of hardwoods or softwoods are expensive and in some case difficult to find. These sheets are also liable to warp. Joining narrow boards end-to-end is time-consuming to prepare and again liable to warp. Advantages of using manufactured boards Manufactured boards are available in large sheets, much wider than is possible to cut from a tree. The boards are stable (do not warp). Unlike timber, they do not absorb moisture, dry out according to the weather, twist and split. Manufactured boards may be sold in standard sheets of 1,525 x 1,525mm or 1,220 x 2,240mm in a variety of thicknesses. Slide 14 MDF Medium Density Fibreboard MDF is a type of hardboard, which is made from wood fibres glued under heat and pressure. There are a number of reasons why MDF may be used instead of plywood or chipboard: It is dense, flat, stiff, has no knots and is easily machined. It is made up of fine particles and does not have an easily recognisable surface grain. It can be painted to produce a smooth quality surface. Because MDF has no grain, it can be cut, drilled, machined and filed without damaging the surface. However, it can be dangerous to use if the correct safety precautions are not taken. MDF contains a substance called urea formaldehyde, which may be released from the material through cutting and sanding. Urea formaldehyde may cause irritation to the eyes and lungs. Proper ventilation is required when using it and facemasks are needed when sanding or cutting MDF with machinery. The dust produced when machining MDF is very dangerous. Masks and goggles should always be worn. Due to the fact that MDF contains a great deal of glue, the cutting edges of your tools will blunt very quickly. Slide 15 MDF (Continued) MDF can be fixed together with screws and nails but the material may split if care is not taken. If you are screwing, the screws should not be any further than 25mm in from the edge. When using screws, always use pilot holes. MDF may be dowelled together and traditional woodwork joints may even be cut. MDF may be glued together with PVA wood glue. Oil, water-based paints and varnishes may be used on MDF. Urea formaldehyde is always being slowly released from the surface of MDF. When painting, it is good idea to coat the whole of the product in order to seal in the urea formaldehyde. Veneers and laminates may also be used to finish MDF. Wax and oil finishes may be us