Editing Metal shaping

Metal shaping is an invaluable skill to have in hot rod fabrication. There are many specialized tools used in the forming process.


Shaping metal is basically as simple as shinking or stretching it to achieve the required shape.


Shrinking metal can be done using a stump and wooden or plastic mallet. A set of tucking forks can also be used but this process can be slow and tedious. A reciprocating machine such as a Pullmax with thumbnail dies can also be used to shrink metal rapidly. This is not a machine for a novice though. Learning to shrink metal by hand is said to be the best way to see how it reacts throughout the process.
In the photo below is a "stump" made from pieces of maple hardwood glued together and then different sized cone shaped cutouts made.

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Stretching metal can be done on a shot bag with a wooden, plastic or steel mallet. The bag is made of leather and filled with a material such as lead shot or sand. Plastic injection molding pellets have been used for this as well.
Metal may also be stretched over a hollow such as the cut out of a stump or even a piece of pipe. In the photo above, one corner of the stump has a 3" dia hole for stretching metal. Shrinking a piece of metal around the edges will result in a bowl like shape. After shrinking the edges to the maximum amount allowed by this process, it then becomes necessary to stretch the center area of the piece to achieve the radius required.


Stretching the edges of a panel only and not working the center at all will achieve the classic potato chip shape. This is called the reverse curve. The streching can be done by holding the edge of the sheet over a cutout in a stump and applying some severe hammer blows. The photo below shows a wooden mallet with a small radius and a panel that has been stretched over the 3" dia cut out.


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The photo below shows both edges of the panel after alot of stretching over the hole on the stump. The edges of the panel were held half over the hole and the edge of the sheet driven into the hole for stretch also. 


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An English wheel (ewheel) can then be used to smooth out the lumps created from the stretching or shrinking processes. If too much pressure is exerted by the ewheel on areas that were shrunk, the material will start to stretch changing the shape. If too much pressure is exerted at the stretched areas, the metal will be stretched even more and change the shape.