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The Corroboree

mounding copper coils

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so my latest project requires an annoyingly difficult to build thing; a copper coil, (electro magnet style) that is wound around a spherical mould so that it's inside is round. the wire will not be wrapped around the entire sphere, only a 40-60mm band around the ball so when removed, will be a ring shape. (sorta.) it needs to have an inside diameter of 120mm at it's largest point. it requires to be around 3-6 turns thick. the wire will be 0.4-0.6mm thick. super glue will be used to bind the wire.

this does not sound too hard, but allow me to explain the problems.

1, the mould needs to be removable. this either means to use a sacrificial ball that can be destroyed to remove or a ball that is soft that can be deflated or squeezed or otherwise miss-shapen so that it can be removed. but must not be too soft or it will become miss shapen as the wire is wound onto this mould

2, finding a method of keeping the wire from sticking to the mould. it is not as easy as it sounds, as many lubricants will stick to the wire as it is being wound, preventing the super glue from binding that wire to it's surrounding wires. the wire needs to be right against the inside of the coil, with little to no layer between the wire and the air inside it. (i once wrapped it around a pvc pipe that was 1mm thick and this was completely unsuitably thick)

3, finding a supplier of a suitable mould and wire. i have estimated i will need a minimum of 300g of wire at a 0.04mm thickness, however 500g wound be best for room for error and fucking around. a ball 120mm is alot harder to find then one would think. especially one that fits with the first problem.

4, rotating the mould to accurately wind the wire on evenly.

i have a few solutions, but they all lead to more questions! :S

a Styrofoam ball would be ideal, however, the super glue would dissolve it, as well as many lubricants may dissolve it also. it would be good to paint it with something that would protect it from the super glue, then eaten away with a solvent (super glue has excellent solvent durability) but i don't know what is a suitable paint. a drill can be poked into this ball and set to a very low speed to accurately wind the coil.

using a ball made of HDPE would be ideal as most glues do not stick to it, however, finding a ball exactly 120mm wide is quite difficult. it also needs to be solid enough to hold its shape with the wire around it. this would be a sacrificial mould and cut out.

just then i built a coil from a small basket ball, coated in carnauba wax, with 100g of 0.4mm thick wire. but it was not enough wire, the wax was stuck to some strands of wire so it never bound to the coil, the coil was not wound accurately and there for tight enough so some wires lifted and finally it was only a 15mm wide band instead of 40mm or so.

so anyway, what have you guys got? any advice for any aspect of this lil project would be greatly appreciated!

i'm kinda stumped and been trying to work this bit out for months :S

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Your best bet would be to seek advice from an "Armature Winder".

If google/etc don't help, ask a local small-motor repairer


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