Wednesday, February 19, 2014

Very small cutter

This question came through YouTube, in response to my combination foam cutter

I am just curious, why aren't these cutters made to be a little smaller and more manageable...something like a little wire that is shaped like a U where the loop is like 1/32" so you can carve intricate stuff, or a cutter that is several inches long, shaped like an F with the wire going between the short lines of the F, where the wire itself is only 3" or so long??  For me, working at the end of that huge thing would be impossible;/

You can make cutters as small as you want, this is just an all-in-one prototype that I came up with. It is a work in progress, and I am moving forward with commercial fabrication. But more on that later.

Long story short, when it comes to a hot wire foam cutter, you're electrical requirements are a function of wire diameter/thickness and wire length. With a bendable wire, you cannot use smaller than 20 gauge wire. That size wire requires about 4-6 amps to become hot enough to cut foam. However, a large gauge wire has little resistance, and at 1/32" length, the maximum applied voltage would be incredibly low. In fact, you could not apply more than 0.007 volts to the circuit before overcoming 6 amps. There are virtually no commercially available power supplies that can micro-control voltage that low.

The solution would be to add a resistor to your circuit, to raise the overall circuit resistance. The best case scenario would be finding a variable voltage power supply, that can out put at least 10 amps. You'd have to find a 1 ohm / 50 watt resistor, and place it in-line with your 1/32" 20ga cutter. Your optimal cutting settings would be ~6 volts, drawing 6 amps from your power supply (36 watts), and not overloading the wattage of your resistor (50 watt max).

A very small cutter is definitely an option with the right tools and electrical supplies. But small resistors that can handle that level of heat dissipation (wattage) are hard to come by. In most circumstances you have to buy them in bulk. That said… I THINK I have 1ohm 50watt resistors in my shop.. I'd just have to look. how can something so simple be so complicated:)  Hey does cutting foam with a hot wire give off any fumes?

Thanks for your response, that was very thoughtful of you

I know!! It is both simple and complex at the same time!

Yes, cutting foam will emit fumes depending on the temperature of your wire. It is a bit of a trade off… A hot wire lets you cut faster but will emit more fumes but a cold wire will cut slower with less fumes. When you have a cold wire, you have to apply more pressure to cut the foam which will increase your chances of breaking the wire. A hot wire usually won't touch the foam because the radiant heat will melt the foam at a distance. Although, the hot wire will cut away more foam (a larger kerf) so sometimes your fine work is lost. Like I said… it's all a series of trade offs. It's a fine balance between temperature, cutting speed, fumes emitted and cutting kerf. 

I hope that doesn't overcomplicate!!

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