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Whether the product is being designed and made by you in school or by an international company, the first step in processing a resistant material is to measure and mark it up accurately. There are a number of processes for shaping [shaping: any process which defines or moulds or changes the shape of an object ] resistant materials, including wasting [wasting: achieving the shape you want by removing the bits you don't want ], deforming [deforming: changing an object's shape without losing any material ], fabricating [fabricating: putting together from separate components ] and reforming [reforming: changing an object's shape by means of changing its state - usually from solid to liquid, then back to solid. ].
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
| Process | Wood | Metal | Plastics |
|---|---|---|---|
| Lines | Pencil | Scriber | Felt-tip pen |
| Lines at right angles to an edge | Carpenter's try square | Engineer's try square | Engineer's try square |
| Lines parallel to an edge | Marking gauge | Odd-leg calipers | Odd-leg calipers |
| Marking for a mortise | Mortise gauge | N/A | N/A |
| Marking a circle | Pair of compasses | Dividers | Dividers |
| Marking the centre of a hole | Pencil | Centre punch | Felt-tip pen |
| Marking an irregular shape | Template | Template | Template |
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
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