This page describes the steps to making a basic T-fold, one of the main categories of fold-forming. Numerous variations are possible from this simple starting place.

To begin with a loop is made from a rectangular piece of sheet metal.
The loop is placed into the vise and the jaws clinched tight onto the loop. The amount projecting from the top determines the width of the table.
The ends of the loop are now malleted down, ‘confirming’ the position of the table relative to the legs. Clinching the ends first leaves a hollow shape to the loop. This is called a pillow.
Here the basic T-fold is taken out from the vise so you can see the shape while it is in the pillow form. It is then replaced in the vise and malleted to obtain the final T cross section.
Here the T-fold is forged. You can choose to forge it as shown to widen the table (top surface of the T-fold)
Or the T-fold can be forged lengthwise. As you can see here. If the T-fold is forged with the legs free like this it will twist like a helix.
If the fold is forged with the legs pinned in the vise then there is no twisting when the T-fold is opened
Here the T-fold has been annealed and opened. Because it was annealed the table opens with a concave curvature. If it is not annealed before opening then the table stays flat.

An example of a T-fold forged with the legs pinned in the vise. On the right is one where the entire table area was thinned with a rounded hammer face, thus arching over the table when annealed and opened

An example of a basic T-fold forged with the legs free. Note how the twisting is modified and affects the table shape upon opening.