Measuring and marking out

Whether you are measuring wood, metal or plastics, you will always use the same measuring tools:

• a steel rule for measuring lengths
• outside calipers for measuring round rods
• inside calipers for measuring holes

Always measure from a baseline [baseline: horizontal line marking a point of origin from which all vertical measurements are made ] or datum surface [datum surface: common horizontal surface from which all vertical measurements are taken ].

• A datum surface is flat and straight. A lot of tasks require two datum surfaces at right angles to each other. Smoothing off will turn a rough, newly-sawn edge into a datum surface.
• To create a datum surface on wood, use a plane.
• To create a datum surface on metal and plastics, use a flat file or hand file.
• Use a steel rule or straight edge to check that a surface is flat. Then check that a surface is at right angles to another surface with a try square.

Marking out

'Marking out' means the transfer of shapes and lines onto the material, as guides for cutting, bending or shaping them. Accurate marking out is essential if the different parts of the product are to fit together properly.

The correct marking-out tools for different materials

Whenever you are cutting and shaping resistant materials, undertake the the following tasks in order:

• Mark out where the material should be cut
• Cut the material, leaving some spare material for finishing to a smooth surface
• Smooth the material to the lines marked out
• Cut any joints
• Final smooth off
• Apply a suitable finish

Shaping by wasting

Shaping by wasting simply means cutting away material to leave the desired shape. It gets its name because the material which is removed, such as shavings or sawdust, is usually thrown away. Shaping by wasting can be done on any type of material.

Shaping by wasting which can be done by hand

Machine wasting

Cutting timber on a circular saw bench

Almost any wasting technique can be mechanised. For health and safety reasons, some of these processes should only be done by a teacher.

Common machines used for shaping by wasting

Shaping machines may also be controlled by computers - an example of computer-aided manufacturing [computer-aided manufacturing: use of computers to assist in any of the phases of manufacturing a product. CAM for short ]. Computer control means the work is more accurate and the task can be more frequently and quickly repeated without any deviation from the standard.

Shaping by deforming: woods and metals

Deforming

Deforming is a method of shaping materials by either bending in a straight line or by creating a bowl or dish shape. The key methods for deforming materials in a straight line or in two dimensions are described below:

Bending

Metals can be bent in a vice or in folding bars. Thin metal may be bent whilst cold, while thicker metal may need heating or annealing [annealing: heating a metal to toughen it, so it will not break when bent. Some metals like copper will go red when hot. With those that don't glow like aluminium, put soap on them first, it will be hot enough when the soap goes black. ]. Larger pieces of metal may also need to be heated first.

The material is marked where it is to be bent, and clamped to the line in the vice or folding bars. To prevent damaging the material as you hit it with the mallet, place a piece of wood next to it and hit that instead.

Laminating

Wood is usually bent by laminating. This is done by cutting thin strips of wood, putting glue on the strips and clamping them into a mould [mould: a hollow form into which a softened material is placed. The material hardens and the mould is then removed to produce a product of the desired shape ].

Three-dimensional deforming

Hollowing and press moulding are both ways of three-dimensional deforming it is important to remember that wood will not deform in three dimensions.

Hollowing

Hollowing is a way of deforming thin sheet metal to produce a bowl shape. The metal is first annealed [annealed: (of metals) heated to make it tougher ] then cooled in cold water. Next it is placed on a leather sand bag and shaped using a bossing mallet. Finally it is placed on a hollowed wooden block and shaped it with a blocking hammer.

Press moulding

Press moulding can be used to force sheet metal into 3D shapes. The metal is placed between two moulds which are then squeezed together until the metal takes on the shape of the moulds.

Shaping by deforming: plastics

Bending

Thermoplastics cannot be bent when cold. They are bent using a strip heater or line bender which will heat the plastic in a straight line, so it can be bent by hand, as shown below.

Sheet of thermoplastic held in a strip heater. Heater bars heat the thermoplastic in a straight line, prior to bending.

Press or compression moulding

A mould is made in two halves - top and bottom. Sheet plastic is placed between the two halves, which are then heated and pressure applied. The heat from the mould causes a chemical reaction in the plastic which enables it to assume the new shape. Press moulding is used to make electrical fittings, handles, and many other products. It can only be used with thermosetting plastics [thermosetting plastics: types of plastic that can only be melted once, and then become very hard ] such as phenol and melamine formaldehyde.

Blow moulding

Blow moulding is used to shape plastics - mainly for making bottles, plastic buckets and similar shapes. A tube of softened plastic called a parison is extruded [extruded: shaped by being forced through an opening ] into a mould, which then clamps one end closed. Air is then blown under pressure into the interior of the parison, which expands to fill the mould and create the desired shape. PVC, polythene and polypropylene are commonly used in blow-moulding.

Vacuum forming

This process uses a wooden mould [mould: a hollow form into which a softened material is placed. The material hardens and the mould is then removed to produce a product of the desired shape ] or formform: A style of poem, with a particular pattern of rhythm, rhyme pattern or regular line length (eg sonnet, couplets or ballad).. A sheet of thermoplastic is heated, then shaped by creating a vacuum [vacuum: A volume that contains no matter - space is almost a vacuum. ] underneath it. Air pressure then forces the plastic over the mould. Vacuum forming is used to for food and confectionary packaging, trays, shop fittings and baths. Suitable thermoplastics include acrylic, polystyrene and PVC.

Shaping by fabrication

Fabrication involves joining separate pieces of material by cutting joints or by using other components [components: The different elements that make up a system or device. ], such as screws, nails and adhesives, or by using heat processes such as soldering [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 ] or welding [welding: joining metals by melting and fusing the adjoining edges or surfaces ]. Fabrication processes can be either permanent or temporary. Temporary fabrications are designed to be easily taken apart.

Fabrication processes and when they might be used

Shaping by reforming

Reforming is a method of shaping materials which changes their overall appearance by first melting or softening them into a paste, then hardening them. Reforming methods include casting, extrusion and injection moulding.

Casting

Most metals can be cast, but in school usually only aluminium is used.

1. Create the required shape in a soft material - usually wood. This is called a pattern.
2. Make a mould by placing the pattern in special casting sand inside a moulding box or flask. The sand is made to stick together using water or oil.
3. The pattern is removed and metal poured into the cavity.

Die casting

Die casting uses a metal mould which can be very detailed. The mould is made in two parts to allow the casting to be removed. Die casting is a very important industrial process used for many different types of products.

Die-cast aluminium engine parts     Injection-moulded plastic hardhat.

Extrusion

Extrusion is used to produce long, but fairly thin products such as pipes or curtain tracks. Both plastics and metal can be extruded. The material is forced through a die, which contains a hole which is the same shape as the required product.

Injection moulding

Injection moulding is a similar process to die casting. A metal mould is used and softened or molten plastic is forced into the mould by pressure from a screw thread or pneumatic plunger. The mould is made in two parts to allow the moulding to be removed. Polythene, polystyrene, polypropylene and nylon are the plastics most often used in injection moulding, which is used extensively in industry.

Information and communication technology (ICT)

ICT can help with designing resistant materials products in many ways:

• Drawings, graphics and diagrams can be produced and edited using graphics or design software.
• Written information about designs can be recorded and edited using word processing software.
• Writing and drawings can be combined using desk-top publishing (DTP) software.
• Pictures of existing products can be scanned and used in graphics, photo-editing or DTP software.
• Database packages can be used to record and analyse survey data.
• Spreadsheet software can be used to make Gantt or other planning charts, to produce graphs and charts, and to help with costing D&T projects.

ICT can help with the making of products in the following ways:

• Shapes printed onto card can be used for templates.
• Text printed out can be glued onto sheet material and cut out.
• Machines for cutting card and self-adhesive vinyl sheet can be used to cut letters or shapes. Complicated shapes can be cut more easily by machine than by hand.
• Computer-controlled lathes can make a number of identical turned parts.
• Computer-controlled milling machines can cut out shapes more easily than by hand, especially recesses in materials. Complicated shapes can be cut more easily than by hand.
• Parts which have fine detail, or need to have accurately fitting parts, can be made more accurately than by hand or manual machine methods.

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