
He gathered some wood and a long hinge
There are 2 U-shaped wooden pieces on either end connected with 4 wooden bars. The front bar has guitar key tuning pieces that are used to tighten the cutting wire (guitar strings). It's hinged at the back and the guitar strings are stretched between the front and back bars.
Attached to the bottom platform is a piece of 2x4 screwed to a taller piece of wood to make an L-shape. It acts as a lip so the soap loaf doesn't slide when the bars are cut.
You might enjoy watching the video we made showing the structure and dimensions of the soap cutter. It's not as polished as the expensive ones offered online, but it didn't cost much to make and it works great!