Instructables

Trying to make a table-mounted hot knife for rope cutting

I'm wanting to build a mountable hot knife for cutting climbing rope, similar to the ones at http://www.wirecare.com/hot-knives.asp and  http://www.rocknrescue.com/acatalog/Table-Hot-Knife.html, using a method similar to flywoodkb's http://www.instructables.com/id/Hot-wire-foam-cutter/. How should I go about keeping the "prongs" coming out of the box from electrocuting me/causing a short? I'm hoping to use a jigsaw blade for the blade part.Also, I have a handful of transformers from disassembling some electronics. Is there a way to tell what voltage and amperage they are?  Any help would be appreciated. Thanks!

Picture of Trying to make a table-mounted hot knife for rope cutting
Goodhart2 years ago
Higher amperage transformers (most are very pricey) would be best; and using an "element" (high resistant, like an electric stove) except it'd need to be straight. I assume nichrome wire is too thin?
The Insomniac (author)  Goodhart2 years ago
What's nichrome wire? I was considering using this thing: http://imgur.com/a/GNPDg from an electricd griddle, but I couldn't figure out where the electrodes would go to. Any ideas? I had thought the center spikey thingey was an element, but it didn't heat up when I plugged it in. Thanks!
The "element" is inside the actual gridle, you just have "input" controls shown.   Nichrome wire is a high resistance wire that will glow bright red at the proper power input levels.   Often used in toasters soldering irons, and hot glue guns, etc. 
The Insomniac (author)  Goodhart2 years ago
Cool! Thanks for the info. I'll see what I can find that's salvageable at my local thrift store. Perhaps I might wrap some nichrome wire around the blade part.
Get yourself one of the old classic Weller "Soldering guns", which looked like an electric drill, with two bars coming from the front, where a wire "tip" was connected between the bars.

Freak out the switch, so you can mount it remotely, make a "tip" the shape of the blade above and connect to the bars.

The voltage on the bars is <<1V.

Steve
Mrballeng2 years ago
What if you just mounted two soldering irons in a platform and connected the two with a long razer blade or even some wire?
The Insomniac (author)  Mrballeng2 years ago
That would require two wires to plug it into, plus that's a bit expensive. Not to mention kind of ugly
I was actually thinking about making one myself. I think I could hack two together for about $5. I'll let you know how it turns out.