This is a spool, developed in OpenSCAD, that can be used to build a solenoid (aka electromagnet) with enameled copper wire. It has two holes on each base, used to insert the wire and to hook it once the solenoid has been rolled. The wire can also help to keep the two pieces together, but I am not sure if that will be enough. Probably gluing them together is safer.

Of course, it can also be used as a generic spool for any kind of wire.

You can modify the following parameters: i_diameter: the internal (core) diameter o_diameter: the outer diameter, on which the solenoid will be twisted i_height: the internal height between bases base_diameter: the bases diameter base_thickness: the thickness of the bases in_hole_offset: the offset of the first hole, where the wire will enter out_hole_offset: the offset of the second hole, where the wire will exit hole_diameter: the holes diameter wedge_height: the height of the wedge wedge_thickness: the thickness of the wedge

Example: solenoid(14, 18, 50, 50, 4, 12, 20, 4); translate([51, 0, 0]) base_only(50, 4, 14, 18, 13, 20, 4, 8, 4);

Thanks to all the guys in #reprap IRC for their suggestions!

1. Print printable.stl (or generate a custom one like in the example above)
2. Assemble the two pieces (and optionally glue)
3. Roll the wire(s).
4. (optional) Fill the core with metal rods and glue
5. Give it current.