How to make a cnc foam cutter
1
Cut a yardstick in half and drill three holes into each piece--one a half inch away from each end and one in the middle. Take the other yardstick and drill a hole 7 inches from one end and another one inch away from the other end.
2
Connect the three pieces together with machine screws (don't tighten them yet), linking the middle hole of one short piece to each hole on the uncut piece. You'll have an H-frame with a handle sticking out on one end. Lay the frame so the handle is on the left side.
3
Cut both ends off a 12-foot-long, two-pronged extension cord and strip an inch of insulation off one conductor wire at one end. Place a machine screw in the top right-hand end of the H-frame with one washer on each side of the stick. Bend and hook the cord's bare wire around the screw where it pokes out the back side. Place another washer on the wire to "sandwich" it between two washers and tighten the bolt with a nut.
4
Split the cord's two conductors apart about 3 1/2 feet. Cut a foot off the wire that is not connected to the frame and connect the rest to the frame's other end in the same way as the first. Tie both wires temporarily to the frame with cable or twist ties to keep them out of the way.
5
Take a 6-foot-long string and loop it between the H-frame's ends on the other side (the ends without wires connected). Thread the string through the holes at these ends to do this. Tie the loop so the two "short sticks" of the frame are parallel when the string loop is at its tightest point.
6
Tightly wrap a guitar string around one of the machine screw "terminals." Make sure the string loop at the frame's other end is tight while you wrap the string around the other terminal. You now have the guitar string running between the "top-side" ends (with the wires) and the other string running between the "bottom-side" ends.
7
Tie another string to one middle screw connecting a short stick to the frame's long stick. Thread the string through the bottom hole on the opposite leg, then to the bottom hole on the first leg (alongside the string loop) and through to the middle screw that doesn't have a string tied to it. You should have a string "X" along the bottom of the frame.
8
Place a rod within the string loop and twist the loop until it begins to feel tight. Pluck the guitar string; if it makes a humming sound, it's tight enough. Slide the rod toward the long ruler so it can lay on top of the rod and keep the loop twisted.
Electrical
9
Connect the frame to the transformer, dimmer switch and hot wire. The extension cord's free-end wires connect to the transformer's yellow wires. Strip the insulation off the nonplug end of an extra electrical cord, then connect one conductor wire to a black transformer wire and the other to a dimmer switch wire. The dimmer's other wire connects to the transformer. Use electrical tape to make sure there are no exposed wires.
10
Place the whole electrical setup inside a project box. Cut a hole in the box that the dimmer switch's dial can fit through. Make sure the box has holes for ventilation.
11
Plug in the cutter's electrical cord with the dimmer turned all the way down. Slowly turn the dimmer up, pick up the frame, and run the guitar string wire across a foam piece to cut it.
