mandrel

The coil can be of any size, and to make it, resistance wire is wound around a piece of wire used as a mandrel.

As the mandrel with the ferrule passed through the tin, the metal was shaped exactly to the mandrel.

The saw is put on the mandrel at an angle, as will be seen, and should be run at a high rate of speed.

The mandrel should be made slightly conical in order to facilitate withdrawal.

This method is very handy with small lenses; the mandrel is turned, and the lens adjusted by hand till the images are immovable.