Shape of External Iron

The iron surrounding a coil could be almost any shape. What shape do you get when your iron is taken from a surplus transformer?

Shape of External Iron

Although transformers are a very convenient source of high-permeability laminated iron, the shapes and dimensions are a little limited. For example, transformers have rectangular cutouts and this shape will have higher leakage flux than round or other configurations.

Also note that transformers rarely have windings thicker than 1" (and never thicker than 2") for heat dissipation reasons, which always limit my optimum projectile length to 2" or less. This is because the projectile travels the distance normally occupied by the transformer’s windings.

The transformer chosen for this project has dimensions that suggest a nail of 1.5 to 2.0" will be optimum.

The diagram below illustrates the typical geometry of all transformer cores, after removing an extra portion of the iron.