JCE Metalwork cheat sheet
JCE Metalwork · Keep the key ideas within reach.
Materials and Material Properties
Ferrous metals contain iron; non-ferrous metals do not. Ferrous metals are magnetic and susceptible to rust.
Low-carbon steel (mild steel) contains 0.05–0.25% carbon; medium carbon 0.25–0.6%; high carbon 0.6–1.4%.
Cast iron contains 2–4% carbon and is brittle but has good compressive strength and vibration damping.
Brass is an alloy of copper and zinc; bronze is copper and tin. Both resist corrosion and have low friction.
Aluminium is lightweight (about one-third the density of steel), corrosion-resistant due to an oxide layer, and a good conductor.
Thermoplastics soften on heating and can be reshaped repeatedly; thermosetting plastics char and cannot be remelted.
Hardness is resistance to indentation or scratching; toughness is resistance to impact; ductility is the ability to be drawn into wire.
Material selection criteria include strength, weight, cost, machinability, corrosion resistance, and availability.
Hand Tools and Bench Skills
A hacksaw blade has 14, 18, or 24 teeth per inch; use 14 TPI for thick sections and 24 TPI for thin tube or sheet.
File teeth are classified as single-cut (one set of parallel teeth) or double-cut (two crossing sets); double-cut removes material faster.
A file card (wire brush) cleans file teeth; chalk rubbed on a file reduces pinning when filing soft metals.
When filing, apply pressure on the forward stroke and release pressure on the return stroke to preserve the teeth.
A cold chisel is ground with a 60° cutting angle for general metalwork; use a softer angle for softer metals.
A centre punch is ground to 90° and used to mark hole positions before drilling; a dot punch is ground to 60°.
A scriber is made from hardened steel and is used to mark lines on metal; never use it as a lever or punch.
A bench vice should be mounted so the top of the jaws is at approximately elbow height when standing.
Machines and Powered Equipment
Drill speed formula: RPM = (cutting speed × 1000) / (π × drill diameter), with cutting speed in m/min and diameter in mm.
For mild steel, high-speed steel (HSS) drills run at about 25–30 m/min cutting speed; for aluminium, about 60–90 m/min.
A centre drill (Slocombe) produces a 60° countersink and a pilot hole in one operation for lathe work.
On a lathe, surface speed is the speed at which the workpiece surface passes the tool; it depends on diameter and RPM.
A pedestal drill must be guarded; clamp work securely and never hold it by hand; remove the chuck key before starting.
A milling machine uses a multi-tooth cutter; climb milling feeds the cutter in the same direction as the workpiece feed.
A bandsaw for metal uses a continuous blade with fine teeth; blade speed and feed rate depend on material thickness.
Before using any powered machine, check guards are in place, the emergency stop works, and the work area is clear.
Joining Methods and Fastenings
Soldering joins metals with a filler alloy that melts below 450°C; brazing uses filler melting above 450°C.
Soft solder is typically a tin-lead or tin-copper alloy; use flux to remove oxides and improve wetting.
Gas welding uses a fuel gas (acetylene) and oxygen; the flame is adjusted to neutral, oxidising, or carburising.
Arc welding uses an electrode and an electric arc to melt the parent metal and form a weld pool.
A rivet is a permanent fastener; the tail is deformed (upset) to clamp the materials together.
Threaded fasteners: a bolt passes through clearance holes and is secured with a nut; a screw threads into one workpiece.
A clearance hole is slightly larger than the fastener diameter; a tapping hole is sized to suit the thread being cut.
Adhesive bonding distributes stress over the joint area; surface preparation is critical for a strong bond.
Measurement, Marking Out and Tolerances
A vernier caliper reads to 0.02 mm (or 0.05 mm) using a main scale and a sliding vernier scale.
A micrometer reads to 0.01 mm; read the barrel scale and add the thimble reading.
A try square checks 90° angles; a combination square can also check 45° and be used as a depth gauge.
A surface plate and a height gauge are used for accurate marking out and measuring from a datum face.
A datum is a reference point, line, or surface from which measurements are taken.
Tolerance is the total permissible variation in a dimension; for example, 25.00 ±0.05 mm gives a tolerance of 0.10 mm.
Allowance is the intentional difference between mating parts; clearance allowance allows movement, interference allowance requires force to assemble.
Always read a measuring instrument squarely, avoid parallax error, and check zero before use.
Technical Drawing, Graphics and Communication
First-angle projection places the view from the left on the right and the view from above below the front view.
Third-angle projection places the view from the left on the left and the view from above above the front view.
A scale drawing shows the ratio of drawing size to real size, e.g. 1:2 means the drawing is half full size.
Orthographic drawings show front, plan, and side views; isometric drawings show three faces in one view.
Dimension lines have arrowheads at each end and a number; extension lines indicate the extent of the dimension.
A section view shows internal features by cutting away part of the object; hatching lines indicate cut material.
Hidden detail is shown with dashed lines; centre lines are shown with long-short-long dashes.
A title block on a drawing gives the part name, scale, material, date, and drawing number.
Design Process and Project Work
The design process stages: identify the problem, research, generate ideas, develop a solution, make a prototype, test and evaluate.
A design brief states the problem and the constraints; a specification lists measurable requirements.
A prototype is a working model used to test and refine a design before production.
Ergonomics is the study of how people interact with products; consider reach, grip, posture, and force.
A flow chart or Gantt chart can plan project tasks, sequence, and time.
Testing and evaluation compare the finished product against the specification to identify improvements.
Health and safety legislation requires risk assessment at the design stage; consider guarding, material hazards, and user safety.
A bill of materials lists all parts, quantities, and materials needed for a project.
Health, Safety and Workshop Practice
Personal protective equipment (PPE) for metalwork includes safety glasses, hearing protection, and safety footwear.
Never wear loose clothing, ties, or jewellery near rotating machinery; tie back long hair.
A risk assessment identifies hazards, evaluates the risk, and records control measures.
The hierarchy of control: eliminate, substitute, engineering controls, administrative controls, PPE (last resort).
Fire triangle: heat, fuel, oxygen. Remove any one to extinguish a fire.
Electrical safety: check plugs, leads, and PAT test labels; do not use damaged equipment.
Keep aisles clear, store tools safely, and report accidents and near misses.
Use the correct lifting technique: bend the knees, keep the back straight, and keep the load close to the body.
Technology, Society and the Environment
Renewable materials (e.g. timber) can be replenished; non-renewable materials (e.g. metals, oil-based plastics) are finite.
Recycling metals saves energy compared with primary extraction; aluminium recycling uses about 5% of the energy needed to make new aluminium.
Life cycle assessment (LCA) considers raw material extraction, manufacture, use, and disposal.
Product design should consider disassembly and material separation to improve recyclability.
Automation and CNC machines increase precision and productivity but can reduce manual jobs.
Sustainable design aims to reduce waste, energy use, and environmental impact over a product's life.
The 6 Rs: reduce, reuse, recycle, repair, rethink, refuse.
Technology can have positive and negative social impacts; consider employment, safety, and accessibility.