Fixing Nicrome Wire to use as a Cutting Edge

So this post doesn't come with any colourful pictures but is a problem that I have come across at work recently and have had to put my mind into coming up with an answer and then the more complicated problem of trying to communicate this to other people.

Nichrome wire is a wire that is often used for its property that when you put a current along its length it will heat up, it is used in heating elements and also for the cutting of polystyrene such as in the making of ceiling tiles or just to cut interesting shapes out of this easily accessible material.

But how do you secure a hot wire enough to apply a current to it and to then keep it under enough tension to use to cut through polystyrene?

Since when a current is applied to the wire it will heat up and this can cause the wire to expand and so any length that has been fixed at both ends would end up being loose and would not cut a straight line. 

So the challenge is to secure the wire and apply a current to it in a way that allows the tension on the wire to stay constant as its length changes. Here the application of a tensioning device such as a spring is an obvious choice but applying the current to this set-up is an interesting problem. 

Securing the wire at one end and then using a spring at the other end of the wire will keep the wire under tension and securing the power input ‘inside’ of these two fixings will mean that the fixings are not part of the circuit and will only be receiving heat from transfer down the wire.

Using this method the wire itself is secured and then the current is applied in a second connection. This could be improved by additionally supporting the wire so that when there is tension on the wire from cutting the polystyrene this doesn’t relay back to the fittings and twist these at all. To add this extra precaution the wire should be lead around a set of bearings.

When using this method it is possible to add the current to the system at the point of the pulleys but if this is done special consideration must be made to make sure that they still rotate other wise the wire will be worn through as it expands and contracts rubbing against the turning point.