How is sheet metal marked, cut, folded and joined to make a product such as a box or tray?
Sheet metalwork: cutting sheet with tin snips and a guillotine, bending and folding on folding bars or a bending machine, and forming joints such as a folded seam, with allowance made for the bend.
How SQA National 5 Practical Metalworking covers routine sheet metalwork: cutting sheet with tin snips and a guillotine, bending and folding on folding bars or a bending machine, forming folded seams, and allowing for the bend so the finished size is correct.
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What this dot point is asking
Fabrication includes making things from sheet metal - boxes, trays and brackets. The SQA expects you to describe cutting, folding and joining sheet, name the tools (tin snips, guillotine, folding bars/bending machine), and understand the bend allowance so the finished size is right. The skill is applied in the practical activity and sampled by the case study.
Marking out and the bend allowance
Cutting sheet metal
- Tin snips (shears): hand tool for short, curved or shaped cuts in thin sheet. Straight, left-hand and right-hand snips suit different curves.
- Guillotine (bench shear): cuts a long, straight edge in one clean stroke; the sheet is held against a back gauge for a square cut.
- Cut just on the waste side of the scribed line, then file the edge to the line if it must be exact.
- Thin sheet is easily distorted, so support it well and avoid bending it as you cut; a clean cut needs less filing afterwards.
Folding and forming
Folding bends the flat sheet into shape.
- Clamp the fold line level with the top edge of the folding bars held in a vice, then bend the metal up by hand or with a mallet.
- A bending machine (folder) does the same job faster and squarer for longer folds.
- Bend to the required angle (usually 90 degrees) and check it with a try square.
Try this
Q1. Name the hand tool used to make short, curved cuts in thin sheet metal. [1 mark]
- Cue. Tin snips (shears).
Q2. State why a bend allowance is added when marking out sheet metal. [1 mark]
- Cue. The metal stretches a little around each bend, so extra material keeps the finished part the right size.
Q3. Explain why the edge of a sheet-metal tray is often folded over. [2 marks]
- Cue. To remove the sharp raw edge so it is safe to handle, and to stiffen the edge so the part is more rigid.
Exam-style practice questions
Practice questions written in the style of SQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
SQA-style Describe4 marksA simple open tray is to be made from sheet steel. Describe how you would mark out, cut and fold the sheet to shape.Show worked answer →
Award up to 4 marks, 1 per correct stage. Mark out the flat shape (the development) on the sheet from a datum edge using a steel rule and scriber, including the area for each side that will be folded up (1). Cut the sheet to the marked outline with tin snips for short or curved cuts, or use the guillotine for a long straight cut, keeping just on the waste side of the line (1). Place each fold line level with the edge of the folding bars (or in the bending machine) and bend the side up to the required angle, usually 90 degrees (1). Work round the tray folding each side in turn, checking each fold is square, and remove any sharp edges before finishing (1). A good answer names tin snips or the guillotine, the folding bars, and works from a datum.
SQA-style Explain3 marksExplain why a bend allowance is added when marking out sheet metal, and why edges are often folded over rather than left raw.Show worked answer →
Award up to 2 marks for the bend allowance and 1 for the folded edge, to a maximum of 3. When sheet is bent, the metal stretches a little around the bend, so extra material (a bend allowance) is added when marking out so the finished part comes out the right size (1); without it the folded part would be too small (1). Edges are folded over to remove the sharp raw edge, which is a safety hazard and can cut the user, and the folded edge also stiffens the part so it is more rigid (1). A clear answer links the allowance to finished size and the folded edge to safety and stiffness.
Related dot points
- Thermal joining: joining metal with heat by welding (e.g. MIG/arc), brazing and soft soldering, the difference between them (melting the parent metal versus a filler), and the safety needed for hot work.
How SQA National 5 Practical Metalworking covers joining metal with heat: welding (MIG or arc), brazing and soft soldering, the difference between melting the parent metal and using a filler, the relative strength of each, and the safety needed for hot work.
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- Finishing processes: removing sharp edges and burrs (deburring), cleaning and preparing the surface (emery cloth/abrasives), and applying a finish such as paint, lacquer or plating to protect the metal and improve its appearance.
How SQA National 5 Practical Metalworking covers finishing a metal product: removing sharp edges and burrs (deburring), cleaning and preparing the surface with abrasives, and applying a finish such as paint, lacquer or plating to protect the metal and improve its appearance.
- Measuring and marking out: using a steel rule, engineer's try square, scriber, odd-leg (jenny) callipers, dividers and a centre punch from a datum edge to transfer a drawing onto metal accurately.
How SQA National 5 Practical Metalworking expects you to measure and mark out a metal workpiece: working from a datum edge with a steel rule, engineer's try square, scriber, odd-leg callipers, dividers and a centre punch so that holes and lines are accurate before cutting.
- Health and safety in the workshop: identifying hazards, using personal protective equipment (safety glasses, apron, gloves where appropriate), guarding machines, keeping a tidy area, and following safe working practices for hot, sharp and rotating processes.
How SQA National 5 Practical Metalworking expects you to work safely: spotting hazards, using personal protective equipment such as safety glasses and aprons, guarding machines, keeping a tidy workspace, and following safe practices for hot, sharp and rotating processes.