Summary

This is an electromagnet demispool, half of the hollow spool for a two inch nail electromagnet.

Instructions

After making the first demispool, check to see that a two inch by one eighth inch diameter common nail fits snugly. If it doesn't, change the dimensions of the demispool hole or alter the skeinforge parameters until you make a snug fitting demispool. Once you've made one snug fitting demispool, make another, and fit the nail through both. Then put wire, preferably fine magnet wire, through the perforations for support, then wind it around the spool to make an electromagnet. Afterwards, the end of the wire can be fitted through the perforations to keep the winding tight.

The base and top demispools are identical, in the picture the base demispool is colored yellow and the top demispool is colored white to distinguish them. The nail is colored blue light grey. The perforations are to provide support for the wire ends and to provide mounting holes to attach the electromagnet to something else.

Besides wrapping the electromagnet by hand, you could also use an electric screwdriver or drill operated on low voltage to turn a one eighth inch drill fitted through the spools. If you the one eighth inch drill is not long enough, you could try a nail with its head cut off so it could fit in the drill chuck, fitted partially through the spools. If neither is long enough, you could cut a one eighth inch pipe, usually available in hobby stores, to length with a small pipe cutter.

The demispool is one inch (25.4 mm) high, half the length of the shaft of a two inch nail. The center hole is one eight of an inch (3.175 mm) in diameter, the diameter of a common two inch nail. The base is 1.2 mm thick, three standard (0.4 mm thick) layers high. The wall thickness of the spool is 2 mm. The perforations are two mm in diameter and they are three mm from the octogon corners. The inner radius of the octogon is 10 mm, the outer radius is 10.82 mm and the sides are 8.28 mm long.

To quickly alter the dimensions of the demispool center hole so that it will make a snug fit you can scale the spool xy, as a side effect this will change the perforation diameter and octogon size. To alter the height of the demispool, you can the scale the spool in the z direction, as a side effect this will change the height of the base.

To change a dimension without side effects, the Art of Illusion file with all the intermediate shapes is included. To change the center hole diameter, change the radius of the nail hole, then subtract the nail hole from the perforated spool to make a new electromagnet demispool. Then convert electromagnet demispool to a triangle mesh, and simplify the triangle mesh. Then select the electromagnet demispool and export it as electromagnet_demispool.stl. To change other dimensions, the entire constuction sequence is the following. Make an octogon polygon then convert it to a mesh, called octogon mesh, extrude that to make the extruded octogon. Subtract the spool negative inner cylinder from the spool negative outer box to make the spool negative hollow cylinder. Subtract the spool negative hollow cylinder from the extruded octogon to make the filled spool. Make perforations 0 though 7, then join them with the join objects script to make the perforations. Subtract the perforations from the filled spool to make the perforated spool. Then subtract the nail hole from the perforated spool to make the electromagnet demispool. After each boolean operation, convert the shape to a triangle mesh, then simplify that mesh by choosing Edit Objects, then choosing Simplify Mesh, to be on the safe side you can then click Optomize Mesh.

Electromagnet Demispool