Why
- Sheet metal is often available as scrap, in the better parts of rusted through oil drums, car wrecks and roof sheets.
- There is much local experience with working with sheet metal.
- The setup of many designs can be based on the use of sheet metal as its special application can be derived from what is already general known
How
- Sheet metal can be cut and bend without machines, simple hand tools like a cutlass and a hammer suffice.
- Sheet metal, specially very thin tin, can be cut by scratching a deep groof in the surface. When bent a few times along this line, it will separate very acurate along this line.
- Sheet metal, of a thicker size from 1.5 to 3 mm. can be cut by hamering a groove with a sharp chisel in the top surface on an envil. When turning round the marks of the cut can be seen. At the same line a second groof is hamered with the chisel. Along this line the sheet can be broken off by bending.
Freeing sheet metal from a drum
The smart trick is to drive the sharp point of an axe along a line marked on some piece of sheet metal. Only the sharp point has to cut through. To let the blade sink deeper in the cut spoils the work. The line can be straight, can make curves or sharp angles. It only takes a little practice to follow the line with the sharp front end of the cutting edge. Fast but light hammer strokes on the flat side of the axe force the cutting. The edge of the cut sheet bends inwards. This can be flattened, by folding it over some more, then flattening the double layer, this makes the edge stiffer, and soft and safe for handling. A drum has strong edges made to shape the connection between bottom and cylinder. Good use of this reinforcement is made by cutting close to the edge. Cutting with the axe is easier when the sheet metal does not bend away from the cutting. But cutting free suspending sheet metal is also easily possible by driving the axe with more horizontal hammer blows at the same time inserting the tip of the axe at a sharper angle to the surface of the sheet metal.
Flattening sheet metal
When an 200 liter oil drum is used to recuperate the sheet metal, the cylindrical shaped side part has to be flattened. This works well by pounding it with a log as shown in the picture. Start in the middle and then works towards the ends.
Folding sheet metal
Folding sheet metal is easy using almost the same method as with cutting. Hammering the axe along, but prevent to make a cut, only make a linear sharp dent in the sheet. Bend over the part that has to be folded. Sometimes it helps to fold over an edge, but with some practice just applying some force and hammer blows does the job. A nice property of this method of folding is the accuracy of the place where the sheet folds. You get it exactly at the line that is dented with the axe.
- Sheet metal is for example used for making Weld wood.