Panel Beating, Shrinking and Stretching
Panel Beating, Shrinking and Stretching
The exam tests metal flow: how hammer blows move steel, how to planish a repair, and when to shrink or stretch so the panel returns to its original contour.
Core rules
- Hammer and dolly: hold the dolly behind the dent and strike the high spot; off-dolly is used to raise low areas.
- Planishing is a series of light, overlapping blows that smooth the surface without thinning the steel.
- Stretching occurs when the metal is hammered outward; a stretched area is proud and has lost its shape memory.
- Shrinking reverses this: heat a small spot to cherry red and quench with a wet rag, or use a shrinking hammer or shrinking disc. Heat must be local and quick.
- Work hardening makes steel brittle; excessive hammering requires annealing, but not on HSLA.
- Aluminium work-hardens faster and needs different hammers and heat control.
Worked example
A dent has been pulled too far and the metal is stretched. Reasoning: the area is now high and "oil-cans" when pressed. Heat a small spot with an oxy-acetylene torch to cherry red, quench it, and planish lightly. The aim is to shrink the stretched zone, not to melt the panel or heat a wide area.
Traps
Overheating a large area, hammering a stretched panel further, and using a shrinking technique on high-strength steel. Also, failing to planish after pulling, leaving a rough surface under the filler.