Damping the swinging cutting wire in my vertical hot wire cutter

My 3D printer has a detachable x-y stage, which makes it very easy to create a hot wire cutter. In fact, that was the first thing I did when I got the x-y stage working. The cutter is very simple: I hang a rope from the roof, with the cutting wire (a steel guitar string) tied to it, and a 12V supply to heat up the guitar string. I added a weight at the bottom to keep the guitar string under tension and vertical. The x-y stage moves the wire horizontally in any shape I want, and I place the foam just below the x-y stage.

A video of this in action:

The only problem with this arrangement is that the wire swings back and forth when I move it, since it’s basically a heavy pendulum. These movements take a lot of time to die down, so I have to slow down the cutter a lot to avoid having wavy cut lines.

I thought that putting the weight in a tub of water would dampen the movement, but that is messy and does not provide great damping.

After seeing one of those videos with magnets falling slowly through a pipe, I had an idea: Why not use a magnetic eddy current brake?

The design is simple: I just attach a strong magnet (scavenged from an old harddrive) to the bottom of the hanging weight, and put a thick piece of aluminium below it on the floor. This works very well: Any swings in the weight is damped out within a few seconds, and it still allows the wire to move freely.

I uploaded a video of it here:

I’m really happy with the result. This means I now have a hot wire foam cutter added to my tools as well.