Drawing Conventions Orthographic Projection A means of producing an accurate working drawing of a 3-dimensional object using (usually) three separate 2-dimensional views (elevations) from three different viewpoints. The most commonly used variation of Orthographic Projection is known as Third Angle.. Isometric Projection A means of producing an accurate drawing of a 3- dimensional object using a combination of 30º lines for lines which are horizontal in real life, and vertical lines for verticals. British Standard Dimensions An internationally recognised set of rules for applying dimensions to working drawings. Millimetres are always used. Materials Styrofoam expanded polystyrene foam in block form, suitable for modelling. Acrylic also known as perspex a type of thermoplastic, available in sheet, block and rod form, in a range of colours as well as transparent and light-gathering. Polystyrene in sheet form used for vacuum-forming. Polymer plastics composed of long chains of molecules. Thermoplastic those polymers (plastics) that have a plastic memory, i.e. once heated and formed, they can be reheated and re-formed as necessary. Thermosetting plastics the other group of polymers which, once heated and formed into the desired shape, cannot be reheated. This is because their molecular structure is much more rigid than that of thermoplastics. Composites those materials created by combining two completely different materials and their properties, examples include GRP & MDF (see below). GRP (Glass-fibre Reinforced Plastic) a composite material using strands (fibres) of glass bonded together by a liquid resin that when set in a mould, gives a tough, durable material.
MDF (Medium Density Fibreboard) a composite material made up of a liquid resin and timber fibres. This is compressed into large boards of uniform thickness, usually 3, 6, 9, 12mm etc. Plywood manufactured board available in large sheet form. Gains its strength from its structure of thin layers of timber with the grain of each layer at 90º to the next. Softwood natural timber from coniferous trees, e.g. pine, spruce. Hardwood natural timber from deciduous trees, e.g. oak, ash, beech. Ferrous metals any metal having an iron content, e.g. mild steel. Mild steel also known as BDMS (bright drawn mild steel), the most common form of steel with properties suitable for many uses. Has a low carbon content and is relatively soft and is therefore easy to cut, shape and drill. Hardened steel steel that has been heated to about 800ºC and quenched in cold water or oil. This creates a steel that is much harder than mild steel (and so can be used to manufacture tools for cutting mild steel) but it is also brittle. Stainless steel an alloy (see below) of steel and (usually) chromium and/or nickel. This retains its shiny finish and is resistant to oxidisation (rust). Non-ferrous metals any metal that does not contain iron, e.g. copper, silver, aluminium. Alloy a mixture of two or more metals to produce a new material with different properties, e.g. brass (copper & zinc), solder (tin & lead). Equipment Set Square triangular drawing instrument in two versions one with 45º angles, the other with 30º/60º angles. Both have one 90º corner. Usually used together with a T square (see below).
T Square as its name suggests, a T shaped drawing instrument used in conjunction with (or sometimes built into) a drawing board to ensure horizontal lines. Craft knife extremely sharp modelling knife for cutting card and paper with accuracy. Cutting mat used to protect surfaces when cutting with a craft knife. Also aids control of the blade. Safety Rule a steel rule shaped to protect fingers when cutting straight lines with a craft knife. Die Cutter a custom made tool made up of steel blades set in plywood, also known as a press knife. Used in industry to cut complex shapes form card, paper and plastic, e.g. cartons, pop-up book components. Try Square L shaped tool with wooden handle and steel blade used for marking right angles when marking out on wood. An all-steel version called an engineers square is used on metal. Marking Knife a sturdy knife with a sharp point used to mark out on wood. Useful for starting off a saw cut, also for preventing splintering at saw exit point. Marking Gauge carpenters tool with adjustable head and steel point. Used for marking out wood along its length, e.g. for joints. Steel Rule usually 300mm long, flat steel rule for measuring and marking out on wood and metal. Tenon Saw standard carpentry saw, used for most simple wood cutting jobs requiring straight cuts. Coping Saw has a narrow blade in a wide frame for cutting awkward shapes. Hacksaw has a flat hardened steel blade held in a long frame for cutting most metals.
Panel Saw large flat flexible bladed saw for cutting through larger sections of timber. Bevelled-edge Chisel sharp tool with blade chamfered all round. Used for removing waste wood from joints. Usually used with a wooden mallet. Smoothing Plane hand tool with adjustable blade used for smoothing surface of wood in direction of grain. Glasspaper commonly referred to as sandpaper. Abrasive available in different grades for smoothing wood and preparing for a finish, e.g. woodstain or varnish. File hardened steel tool available in various shapes, sizes and degrees of abrasiveness. Used for removing sharp edges from metal and plastics. Disc Sander machine tool with rotating disc of abrasive paper, used to smooth end-grain of natural timber, also suitable MDF, plywood and acrylic. Belt Sander machine tool with continuous rotating belt of abrasive paper, similar in application to disc sander. Pillar Drill machine tool with an adjustable table (to which material is clamped) and powered drill chuck mounted on a fixed pillar. Scroll Saw machine tool with oscillating blade (identical to blade used in coping saw) for cutting complex shapes from wood and plastics. Vacuum Former machine that employs a heater and a vacuum pump to shape thermoplastics over a mould (usually wood). Strip Heater a hot electric element used to heat a narrow area on a sheet of thermoplastic so that the process of line-bending can take place. Scriber a thin hardened steel tool with a sharp point used for marking out on metal.
Centre punch another hardened steel tool with a sharp point, but much sturdier than the scriber. Used to mark out drill centres, by striking with a hammer, on metal so that drilling can begin without the tip of the drill skidding about. Tinsnips cutters for thin sheet metal. Centre Lathe machine tool for carrying out a number of operations on metal. These include reducing diameter of rods, creating an external thread and drilling in the centre of a metal bar. Processes Vacuum Forming the process of heating a sheet of thermoplastic, forcing it over a prepared mould and drawing out all of the air under it to create a hollow shape (see also vacuum former above). Injection Moulding the process of forcing molten plastic into a mould (usually in at least 2 parts) to create solid objects. Line Bending the process of heating a narrow area of a sheet of thermoplastic so that the sheet can be folded to a certain angle (see also strip heater above)