If you look carefully, the fuse wire ‘blade’ is stretched between the switch near the top right corner and the end of the red wire on the left. It is important to use fuse wire. Normal wire will not heat up enough to cut the foam, or it requires a much more powerful energy source that is in my opinion unsafe.
The fuse to protect the power unit is the white ceramic fuse in the centre of the photo. The code is 10W 3R3J.
The push switch allows an easy to control method of putting current through the fuse wire.
I used insulated wire of about 50cm length with alligator clips to connect to the fuse wire and the switch to the power supply. Using insulated wire like this provides a high degree of flexibility in being able to place and move the blade where you need to make a cut.
The circuit is:
Power Supply / short insulated wire / fuse / black insulating wire / switch / fuse wire / red insulating wire / power supply
The variable power supply is useful for two reasons: 1) adjusting the power changes how hot the wire gets and therefore how quickly it cuts through the foam. Sometimes it is better to have a lower temperature to make a slower, more precise cut, and 2) the amount of resistance varies according to how long the fuse wire blade is. The variable power allows you to adjust the power output to match the length of the wire.
Care is needed when cutting because the wire can get very hot and it is very easy to give yourself a minor burn. However, a high heat also makes it easier and much faster to carve the foam.
The standard foam block is 600 x 600 and comes in thicknesses of 25mm, 50mm, 75mm and 100mm. I ordered a non-standard size of 1200 x 600 to reduce the number of pieces that had to be joined and to minimise the potential for gaps to appear during play.
The base is 25mm thick and most of the layers are 100mm thick.
Step 1. Layout the uncut blocks.