S2 Exam: Manufacturing The choice of materials and manufacturing processes plays a significant role in design of various products. In order to explore these fully the designer must be aware of the properties of the materials and the manufacturing processes, which may be used. It takes many years for some types of trees to grow. As the forests of the world are presently being used up, many of the slow growing hardwoods are becoming very scarce. Modern forestry methods use fast growing conifer trees, which can be harvested and replanted in a shorter space of time. With careful management it is possible to control the supply and demand of these softwood trees. Hardwoods Hardwood comes from deciduous trees, i.e. trees which loose their leaves. These trees typically have big, broad leaves and also tend to be slow growing which makes their wood more expensive. Hardwoods tend to be more durable than softwoods and offer a greater choice of texture and colour. The following examples detail some of the more widely used hardwoods: Name of Wood Characteristics Uses Beech Straight- grained wood. Fine even texture. Whitish brown, which turns Cabinet making, curved furniture, interior joinery, veneers and plywood. yellowish brown on exposure. Oak Straight grained. Course texture. Pinkish red in colour. Furniture, flooring, boat building, veneers. Ash Straight grained. Course texture. Whitish to pale brown in colour. Sport equipment, tool handles, cabinet making, veneer and furniture. Mahogany Straight or interlocking grain. Medium Interior panelling, boat planking, Teak Walnut Balsa Softwoods texture. Reddish brown to deep red. Straight or wavy grained. Course uneven texture with oily feel. Golden to darker brown. Very expensive. Straight to wavy grain. Grey brown with darker streaks. Open straight grain. Vary pale beige to pinkish colour. Softest and lightest commercial hardwood. carving, pianos, veneers. Interior and exterior joinery, garden furniture, veneers. Furniture, musical instruments, carving, veneers. Insulation, buoyancy aids, model- making, packaging. Softwood comes from coniferous trees. These trees never loose their leaves hence there are commonly known as evergreen trees. There leaves are thin and needle- like. These trees tend to grow quickly which makes their wood cheaper to use commercially. Softwoods are easily identified by their light colour and open grain pattern. The following examples detail some of the more widely used softwoods. Name of Wood Characteristics Uses Scots Pine Light coloured, usually white yellow to Furniture, construction work, joinery yellow brown. Red Cedar Relatively soft, aromatic timber. Reddish brown to silver grey (after Shingles, exterior cladding, greenhouses, sheds and beehives exposure to weather) Parana Pine Straight grain. Even texture. Light to Joinery, furniture, turnery. Spruce (white wood) Manufactured Boards dark brown with red streaks. Straight grain. Even texture. Almost white to pale brown. Construction, joinery, plywood, piano soundboards, violin bellies. Manufactured boards are being used more and more in both home and industry and they have several advantages over natural timbers. They have strength in all directions due to criss- crossing of grain in each layer, are more resistant to changes in temperature and humidity and board sizes are greatly increased. Manufactured boards roughly fall into three categories: laminated boards, fibreboards and particle boards.
Laminated Boards such as plywood s are constructed from thin sheets of wood bonded in layers to form a strong, stable board. The grain of each alternate sheet is laid at right angles to the next. This construction produces a stable and warp resisting board. Most plywood s have an odd number of veneers to give a balanced construction, the minimum being three. Plywood is available in a range of sizes. Blockboard differs from plywood given that the core is made from square blocks of wood laminated with a layer of ply on each side. Fibreboards are constructed from wood that has been reduced to a fibrous state and added to a bonding adhesive then compressed into boards. Boards of various density are produced depending on the pressure applied and bonding material used. Particle boards are constructed from flakes or chips of wood bonded together under pressure. Depending on the size of the wood particles various types of board are produced. Chipboard is most commonly used although it will swell if exposed to moisture and will not recover. Can be veneered for internal structures. Name of Wood Characteristics Uses M.D.F (medium density fibreboard) Two smooth surfaces. High strength. Furniture with intricately shaped parts Excellent edge quality. or large smooth surfaces. Carcass Plywood Block board Chipboard Hardboard Veneer An odd number of veneers are laid at 90 degrees to each other with the surface parallel to the grain. Timber strips are laid parallel with veneers glued either side with the grain running crosswise Wood chips are mixed with bonding mixture (glue) to create large flat boards. Surface strength depends on chip/ particle size Standard hardboard was one smooth surface and the other embossed. Thin sheets of wood cut from a log for constructional or decorative purposes. Wide variety available. Usually glued to one of the other types of board above before use. construction. Interior joinery, carcass construction. Decorative ply is mainly used for panelling. Shelving and worktops. Furniture, flooring, flat roof construction, kitchens and bathrooms. Walls and ceiling linings, panelling, partitions, shop fitting displays. Furniture restoration. Wall panelling, furniture making, violin backs.
Joining wood There are a large number of different woodworking joints that can be used to construct products. The type chosen will depend on various factors such as: The type of material being used The strength required The direction of the force applied The aesthetic look of the product The quantity to be produced Woodwork joints are typically split into two categories: frame or carcase. Each joint differs in strength and complexity, the more complex the joint, the stronger it will be. You should take your time and pay attention when marking out and cutting a woodworking joint. Accuracy is very important for a good fit and special tools have been developed to help you with this. Frame joints are typically used in items such as tables and chairs where as carcase joints are used when constructing products from sheet material such as kitchen units and wardrobes. Typical Frame Joints Rub (Butt) Joint Half Lap Dowel* Cross Halving
Mitre Finger Mortise & Tenon Typical Carcase Joints Rebate Through Housing Stopped Housing Dowel* *A dowel joint can be used as both a frame and carcase joint.
Planning for manufacture A working drawing is required to help you build your product. It should consist of several views (orthographic) showing dimensions and the details of all the individual parts of your product. A cutting list is a table showing which materials you are going to use and what size each part needs to be cut too before it is shaped and assembled.
Woodworking Tools Being able to measure and mark out accurately is essential to high quality manufacturing. There is a wide range of tools available for a variety of different materials. It is very important that you choose the correct tool for the task and use it properly. Steel Rule: used to measure lengths and has a zero end allowing you to measure from a corner or surface. All sizes are in millimetres (mm) Blade Thumbscrew Stem Stock Try Square: commonly used as a guide to allow a pencil line to be drawn at right angles (perpendicular) to an edge. Stock Spur Marking Gauge: used to mark a single line parallel to an edge of a piece of wood. Marking Knife: A marking knife is used to scribe a line to be followed by a hand saw or chisel when making woodworking joints Brass Back Blade Handle Bevelled Edge Chisel: the most common type of chisel, its bevelled sides allow it into tight corners making it ideal for cleaning up wood joints. Tenon Saw: Sometimes referred to as a back saw due to the distinctive steel or brass strip that runs across its length, designed to stiffen the thin blade. The tenon saw is used for general woodwork and best suited to cutting thin wood and wood joints. Sawing Board: Also known as a bench hook, these are used to hold wood while it is being cut. They can be placed in the vice or hung over the edge of the bench and prevent the wood from slipping. It also protects the bench during cutting. G- Clamp: Available in a variety of sizes and used to hold work to a bench or cramp small projects together. Use scrap wood to protect the surface of your material when the cramp is tightened. Flat File: this type of file is used for long, flat edges and outside curves. PVA Glue: Polyvinyl acetate is commonly referred to as wood glue, white glue, carpenter's glue, school glue or PVA glue. It is water- soluble meaning it dissolves in water and should therefore not be used where products may get wet (i.e. boat building, outdoor furniture)
Finishing Both natural timbers and man- made boards require some sort of finish. Finishes are typically applied to wood to improve the look of some cheaper timbers or man- made boards or to enhance the final look of more expensive woods. Finishes can also be used to provide a protective layer making your product more durable, safe and weather resistant. It is important to prepare the surface of the wood before applying your chosen finish. You should sand your product several times with various grades of glass paper (coarse, medium then fine) remembering to sand in the direction of the grain. You make also use a sanding (cork) block to help you as well as using a damp paper towel to wet the wood and raise the grain in- between sanding (natural timbers only). Glass Paper (Sometimes called Sand Paper) Cork Block The choice, application and preparation of the finish depend on: The material being used The purpose of the finish Where the product will be used Who will use the product How long the product is expected to last Polyurethane Varnish provides a clear surface coating which enhances the natural look of the product and provides a hardwearing, durable surface. To achieve a good finish you should varnish your product at least twice, sanding lightly in- between coats. You may also use paints, stains, oils and waxes to finish woods. All of these finishes are typically oil based therefore you must use white spirit to remove them from your hands/ clean your brushes after use.
Workshop Safety (Re- cap) Everyone has a responsibility to act safely in the workshop and make sure their actions do not put themselves or others in danger. DRESS SAFELY Take of your jacket, and always wear an apron to protect your clothes. If you have long hair it must be tied back. Jewellery should not be worn in the workshop to save you from being caught in tools and materials. You must wear sensible footwear to protect your feet. Wear safety goggles when using ALL machines and when advised by your Teacher. BEHAVE SAFELY Workshops are dangerous places, so never fool around. Never run or play in a workshop. You must never work alone or without permission in any workshop or practical area. Always work with safety in mind, remember that an accident can have serious effects on you or your friend. WORK SAFELY Make sure you follow your Teachers instructions on how to use any particular tool, never try shortcuts and if in doubt ASK! Take care when carrying tools or materials. Carry sharp tools close to your body with the blade facing downwards. Never misuse tools of any sort. Return all tools to the appropriate place after use. Keep your bench tidy Check your bench/ tools at the start of the period & report any broken or unsafe tools to your Teacher. MACHINE SAFETY Only use a machine when you have permission and the correct training on how to use it. If you don't know, don't use it! Always use Safety guards and the safety equipment provided. There must never be more than one person operating or near a machine at any one time. Know where the EMERGENCY STOP BUTTONS are located and use them only in an emergency, it can be dangerous to push them just for fun. Clean machines after use and report any damages or breakages to your Teacher so he/she can have them fixed. CLEANLINESS Always put your material in the proper container/cupboard and wash your hands before leaving the workshop.