Sheet Metal Work: notes

Materials

• Common sheets: mild steel, galvanised steel (zinc coated), aluminium, tinplate and copper.
• Gauge: the thickness of sheet. A higher standard wire gauge number means thinner sheet.

Marking out and cutting

• Pattern development: drawing a flat shape that folds into the final object. A box needs a cross shaped development with allowances for joints.
• Allowances: extra metal added for seams, laps and wired edges.
• Straight snips: cut straight lines. Bent snips: cut curves.
• Guillotine: cuts long straight lines in sheet.

Forming

• Folding bars and bending machine: make sharp bends along a line.
• Stakes and mallets: a mallet of wood or rawhide shapes metal without marking it.
• Rolling machine: forms cylinders.

Joints and edges

• Lap joint: one sheet overlaps the other and is riveted or soldered.
• Grooved seam: two folded edges hooked and closed, strong and used on buckets and pipes.
• Wired edge: a folded edge wrapped around a wire to stiffen it and remove sharp edges.
• Notching: cutting corners away so folds do not bunch up.

Safety

• Sharp edges: file or fold them and wear gloves when handling sheet.