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  1. #1
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    Aug 2012
    Tucson, AZ
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    Cutting ripstop nylon with a hot wire knife

    First off, I'm a tinkerer and always looking for a project. So about a year ago I made a hot wire knife to use to cut foam for a gun case. Basically it is a power supply that feeds power though a certain type of wire (like the kind in electric heaters). The heater wire heats up and cuts through the foam, or anything that melts. There are probably cheaper ways to go, but I sort of followed these plans and have not burnt up the transformer: Disclaimer: don't mess with electricity unless you know what you are doing.

    Fast forward about a year and thanks to great instructions here, I'm working on some new projects. Most recently some DIY snakeskins, and soon a DIY hammock (thanks to creativeKayt for the inspiring videos). I have all this ripstop nylon to cut and I wonder if there is a better way than scissors followed by flaming the edges to keep them from tattering. So I decided to give the hot wire knife a try. Here are my observations:

    1. Way faster than cutting and then flaming the edges.
    2. No worries about catching the fabric on fire while flaming the edges (that happened to me once and took out far more than my deviations from the straight line with the hot wire knife).
    3. It can easily cut through many layers at a time (I've cut nylon webbing and shock cord with it).

    1. It is always cutting, so if you slip it will melt through it. If you need to take a break in the middle of a cut...too bad.
    2. Difficult to get a super straight cut (but once I got the hang of it easily stayed within about 1/8 of a ripstop grid and 1/4 to 1/2 a grid when I repositioned my hands).
    3. I cut the fabric doubled over for symmetry and the edges of two layer stuck together, but pulled apart fairly easily.
    4. Similarly, sometimes the two pieces would fuse back together, but again they pulled apart fairly easily.

    Other thoughts:
    I wish the table on the hot wire knife was a little bigger (but it was cheap from a garage sale before I re-purposed it).
    Having a helper is nice because they can help pull the two pieces apart so they don't fuse back together.
    Don't cut with the wire glowing red hot, it cuts much better when it is not as hot

    Here is the hot wire knife table, (the thin black wire does the cutting).

    Here are the controls for the hot wire knife.

    Here is a section of camo ripstop I cut with the hot wire knife. Notice the chunk missing in the top center, that is where stopped to reposition my hands and the fabric slipped a is always cutting.


  2. #2
    Senior Member Ramblinrev's Avatar
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    Be extremely carefully using a hot knife, or any kind of cutting implement on closed cell foam such as Styrofoam. It can release extremely toxic vapors. Using a heat source to cut synthetic fabric can also release toxic vapors but it is less of an issue than with foam. Always make sure you have good to excellent ventilation.
    I may be slow... But I sure am gimpy.

    "Bless you child, when you set out to thread a needle don't hold the thread still and fetch the needle up to it; hold the needle still and poke the thread at it; that's the way a woman most always does, but a man always does t'other way."
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  3. #3
    New Member
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    Jul 2010
    Sydney, Australia
    That machine looks really cool though might be overkill - not being able to rest in the middle of a cut is tough too. I've always been able to get by with a soldering iron and a ruler.

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