If the metal was stretched during the collision or during repair, it will become loose and "pop" back and forth when pressed (oil-canning). To fix this, heat the center of the stretched area with an oxy-acetylene torch until it is dull red, then quickly quench it with a cold, wet rag or apply a shrinking hammer over a dolly to draw the molecules back together. Step 5: Final Metal Finishing
Tools and materials checklist
Switch to a finishing hammer and a matching contour dolly. Use fine, precise hammer-on-dolly strikes to smooth out the remaining texture. Step 5: Guide Coat and File Check
In this method, the dolly is placed under a low spot, while the hammer strikes an adjacent high spot. If the metal was stretched during the collision
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Planishing high ridges without leaving distinct hammer marks Step-by-Step Metal Bumping Process
Use a body file to identify high and low spots. High spots will be shiny; low spots will remain dull. Use fine, precise hammer-on-dolly strikes to smooth out
Has a highly polished, slightly crowned face to blend out minor imperfections without leaving marks.
The hammer blow pushes the ridge down, while the rebound of the dolly pushes the low spot up.
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The central thesis of the book is that body damage is a series of (peaks) and V-channels
With 50% of new cars using aluminum closures, the is worth its weight in gold here.