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  • bobvick commented on flywoodkb's instructable Hot wire foam cutter6 months ago
    Hot wire foam cutter

    Here's my experience:The idea of a dimmer and transformer didn't make sense to me and didn't work for a lot of people, so I went with a car battery charger with a 2A current limit setting. This worked, but the guitar string broke after about 30 seconds. I tried 3 different strings of different gauge and composition with the same result. I finally got some 22 gauge nichrome wire. At 15 inches it is 1.1 ohms cold. At 2A this would be around 4.4 watts (W=I^2*R), which doesn't seem like enough, but actually it gets plenty hot and works fine. I vaguely remember that light bulb resistance goes up by around a factor of 10 when it heats up. Maybe that's what's going on - a 44 watt light bulb would be plenty hot. Probably a much lighter gauge would work fine as well, but may not be as str...see more »Here's my experience:The idea of a dimmer and transformer didn't make sense to me and didn't work for a lot of people, so I went with a car battery charger with a 2A current limit setting. This worked, but the guitar string broke after about 30 seconds. I tried 3 different strings of different gauge and composition with the same result. I finally got some 22 gauge nichrome wire. At 15 inches it is 1.1 ohms cold. At 2A this would be around 4.4 watts (W=I^2*R), which doesn't seem like enough, but actually it gets plenty hot and works fine. I vaguely remember that light bulb resistance goes up by around a factor of 10 when it heats up. Maybe that's what's going on - a 44 watt light bulb would be plenty hot. Probably a much lighter gauge would work fine as well, but may not be as strong. The wire does get loose with heat. Instead of the ingenious tensioning method described, I used a guitar tuner, which I can tighten when the wire heats up and loosen after using. This thing cuts through styrofoam like butter.I'm thinking about making a contraption that will run between the chuck and the base hole of my drill press (properly insulated!) so that I can get more accurate right angle cuts by guiding the styrofoam through it.

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